resistors resistors limit current, create voltage drops all resistors are rated in both a fixed...
TRANSCRIPT
RESISTORS
Resistors limit current create voltage drops All resistors are rated in both a fixed ohm value of resistance and a power
rating in watts (Watt = Volts X Amps)
Unit -- Ohm Ώ
resistor in series with an LED
Enough current flows to make the LED light up But not so much that the LED is damaged
TYPES
1 Fixed Resistor
2 Variable Resistor
Fixed Resistor Electric symbol Generic Variable Resistor Electrical Symbol
FIXED RESISTORS
bull Fixed-value resistors are divided into two category types of resistors Carbon Metal Oxide and Wire-Wound
Carbon and Metal Oxide flm Wire wound
CARBON RESISTORS
bull Carbon resistors are commonly used in electronic systems bull Carbon is mixed with binder bull the more carbon the lower the resistance bull Carbon resistors have a fixed resistance value and are used to limit current
flow bull They are rated in watts and most have color-code bands to show the
resistance value bull A typical resistor has a watt rating from 0125W to 20 W
Carbon Metal Oxide film
WIRE-WOUND RESISTORS
bull Made with coils of resistance wire
bull Often enclosed in ceramic to help dissipate heat and protect the resistor wire
bull Accurate and heat stable
bull The resistance value is often marked
bull Used in higher watt circuits often 2W or higher
bull An ignition ballast resistor is an example of a wire wound resistor
VARIABLE RESISTORS
bull Resistance increases with increasing length It is possible to use this effect to build a variable resistor
bull Resistance can be altered by changing the length of resistor in the circuit The device below allows just that
Rotating the knob alters the length and in turn the resistance
Types
bull Rheostat
bull Potentiometer
bull Trimmer
RHEOSTAT
bullRheostats have two connections
bullone to the fixed end of a resistor and the other to a sliding contact on the resistor
bullTurning the control moves the sliding contact away from or toward the fixed end increasing or decreasing the resistance
bullRheostats control resistance thus controlling current flow
RHEOSTAT OPERATION
bull As the wiper moves along the rheostat it exposes more or less of the resistor Moving the wiper towards the high places a small portion of the resistor in series with the light causing the light to glow bright Moving the wiper toward the low places a larger portion of the resistor in series with the lamp this increased resistance causes less current to flow lowering the intensity of the light Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
TYPES
1 Fixed Resistor
2 Variable Resistor
Fixed Resistor Electric symbol Generic Variable Resistor Electrical Symbol
FIXED RESISTORS
bull Fixed-value resistors are divided into two category types of resistors Carbon Metal Oxide and Wire-Wound
Carbon and Metal Oxide flm Wire wound
CARBON RESISTORS
bull Carbon resistors are commonly used in electronic systems bull Carbon is mixed with binder bull the more carbon the lower the resistance bull Carbon resistors have a fixed resistance value and are used to limit current
flow bull They are rated in watts and most have color-code bands to show the
resistance value bull A typical resistor has a watt rating from 0125W to 20 W
Carbon Metal Oxide film
WIRE-WOUND RESISTORS
bull Made with coils of resistance wire
bull Often enclosed in ceramic to help dissipate heat and protect the resistor wire
bull Accurate and heat stable
bull The resistance value is often marked
bull Used in higher watt circuits often 2W or higher
bull An ignition ballast resistor is an example of a wire wound resistor
VARIABLE RESISTORS
bull Resistance increases with increasing length It is possible to use this effect to build a variable resistor
bull Resistance can be altered by changing the length of resistor in the circuit The device below allows just that
Rotating the knob alters the length and in turn the resistance
Types
bull Rheostat
bull Potentiometer
bull Trimmer
RHEOSTAT
bullRheostats have two connections
bullone to the fixed end of a resistor and the other to a sliding contact on the resistor
bullTurning the control moves the sliding contact away from or toward the fixed end increasing or decreasing the resistance
bullRheostats control resistance thus controlling current flow
RHEOSTAT OPERATION
bull As the wiper moves along the rheostat it exposes more or less of the resistor Moving the wiper towards the high places a small portion of the resistor in series with the light causing the light to glow bright Moving the wiper toward the low places a larger portion of the resistor in series with the lamp this increased resistance causes less current to flow lowering the intensity of the light Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
FIXED RESISTORS
bull Fixed-value resistors are divided into two category types of resistors Carbon Metal Oxide and Wire-Wound
Carbon and Metal Oxide flm Wire wound
CARBON RESISTORS
bull Carbon resistors are commonly used in electronic systems bull Carbon is mixed with binder bull the more carbon the lower the resistance bull Carbon resistors have a fixed resistance value and are used to limit current
flow bull They are rated in watts and most have color-code bands to show the
resistance value bull A typical resistor has a watt rating from 0125W to 20 W
Carbon Metal Oxide film
WIRE-WOUND RESISTORS
bull Made with coils of resistance wire
bull Often enclosed in ceramic to help dissipate heat and protect the resistor wire
bull Accurate and heat stable
bull The resistance value is often marked
bull Used in higher watt circuits often 2W or higher
bull An ignition ballast resistor is an example of a wire wound resistor
VARIABLE RESISTORS
bull Resistance increases with increasing length It is possible to use this effect to build a variable resistor
bull Resistance can be altered by changing the length of resistor in the circuit The device below allows just that
Rotating the knob alters the length and in turn the resistance
Types
bull Rheostat
bull Potentiometer
bull Trimmer
RHEOSTAT
bullRheostats have two connections
bullone to the fixed end of a resistor and the other to a sliding contact on the resistor
bullTurning the control moves the sliding contact away from or toward the fixed end increasing or decreasing the resistance
bullRheostats control resistance thus controlling current flow
RHEOSTAT OPERATION
bull As the wiper moves along the rheostat it exposes more or less of the resistor Moving the wiper towards the high places a small portion of the resistor in series with the light causing the light to glow bright Moving the wiper toward the low places a larger portion of the resistor in series with the lamp this increased resistance causes less current to flow lowering the intensity of the light Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
CARBON RESISTORS
bull Carbon resistors are commonly used in electronic systems bull Carbon is mixed with binder bull the more carbon the lower the resistance bull Carbon resistors have a fixed resistance value and are used to limit current
flow bull They are rated in watts and most have color-code bands to show the
resistance value bull A typical resistor has a watt rating from 0125W to 20 W
Carbon Metal Oxide film
WIRE-WOUND RESISTORS
bull Made with coils of resistance wire
bull Often enclosed in ceramic to help dissipate heat and protect the resistor wire
bull Accurate and heat stable
bull The resistance value is often marked
bull Used in higher watt circuits often 2W or higher
bull An ignition ballast resistor is an example of a wire wound resistor
VARIABLE RESISTORS
bull Resistance increases with increasing length It is possible to use this effect to build a variable resistor
bull Resistance can be altered by changing the length of resistor in the circuit The device below allows just that
Rotating the knob alters the length and in turn the resistance
Types
bull Rheostat
bull Potentiometer
bull Trimmer
RHEOSTAT
bullRheostats have two connections
bullone to the fixed end of a resistor and the other to a sliding contact on the resistor
bullTurning the control moves the sliding contact away from or toward the fixed end increasing or decreasing the resistance
bullRheostats control resistance thus controlling current flow
RHEOSTAT OPERATION
bull As the wiper moves along the rheostat it exposes more or less of the resistor Moving the wiper towards the high places a small portion of the resistor in series with the light causing the light to glow bright Moving the wiper toward the low places a larger portion of the resistor in series with the lamp this increased resistance causes less current to flow lowering the intensity of the light Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
WIRE-WOUND RESISTORS
bull Made with coils of resistance wire
bull Often enclosed in ceramic to help dissipate heat and protect the resistor wire
bull Accurate and heat stable
bull The resistance value is often marked
bull Used in higher watt circuits often 2W or higher
bull An ignition ballast resistor is an example of a wire wound resistor
VARIABLE RESISTORS
bull Resistance increases with increasing length It is possible to use this effect to build a variable resistor
bull Resistance can be altered by changing the length of resistor in the circuit The device below allows just that
Rotating the knob alters the length and in turn the resistance
Types
bull Rheostat
bull Potentiometer
bull Trimmer
RHEOSTAT
bullRheostats have two connections
bullone to the fixed end of a resistor and the other to a sliding contact on the resistor
bullTurning the control moves the sliding contact away from or toward the fixed end increasing or decreasing the resistance
bullRheostats control resistance thus controlling current flow
RHEOSTAT OPERATION
bull As the wiper moves along the rheostat it exposes more or less of the resistor Moving the wiper towards the high places a small portion of the resistor in series with the light causing the light to glow bright Moving the wiper toward the low places a larger portion of the resistor in series with the lamp this increased resistance causes less current to flow lowering the intensity of the light Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
VARIABLE RESISTORS
bull Resistance increases with increasing length It is possible to use this effect to build a variable resistor
bull Resistance can be altered by changing the length of resistor in the circuit The device below allows just that
Rotating the knob alters the length and in turn the resistance
Types
bull Rheostat
bull Potentiometer
bull Trimmer
RHEOSTAT
bullRheostats have two connections
bullone to the fixed end of a resistor and the other to a sliding contact on the resistor
bullTurning the control moves the sliding contact away from or toward the fixed end increasing or decreasing the resistance
bullRheostats control resistance thus controlling current flow
RHEOSTAT OPERATION
bull As the wiper moves along the rheostat it exposes more or less of the resistor Moving the wiper towards the high places a small portion of the resistor in series with the light causing the light to glow bright Moving the wiper toward the low places a larger portion of the resistor in series with the lamp this increased resistance causes less current to flow lowering the intensity of the light Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
RHEOSTAT
bullRheostats have two connections
bullone to the fixed end of a resistor and the other to a sliding contact on the resistor
bullTurning the control moves the sliding contact away from or toward the fixed end increasing or decreasing the resistance
bullRheostats control resistance thus controlling current flow
RHEOSTAT OPERATION
bull As the wiper moves along the rheostat it exposes more or less of the resistor Moving the wiper towards the high places a small portion of the resistor in series with the light causing the light to glow bright Moving the wiper toward the low places a larger portion of the resistor in series with the lamp this increased resistance causes less current to flow lowering the intensity of the light Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
RHEOSTAT OPERATION
bull As the wiper moves along the rheostat it exposes more or less of the resistor Moving the wiper towards the high places a small portion of the resistor in series with the light causing the light to glow bright Moving the wiper toward the low places a larger portion of the resistor in series with the lamp this increased resistance causes less current to flow lowering the intensity of the light Rheostats are not used on computer circuits because of temperature variations on the resistor when the wiper arm is moved
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
POTENTIOMETERbull Used to measure changes in position
bull Have three connections or legs the reference signal and ground
bull The reference is at one end of a resistor and the Ground is at the other end
bull Current flows from the Reference through the resistor to Ground creating a voltage drop across the resistor
bull The Signal is a sliding contact (movable wiper arm) that runs across the resistor Unlike a rheostat its main purpose is not to vary
resistance but to vary the voltage in a circuit
Potentiometer Symbol Variable Resistor Symbol
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
POTENTIOMETER OPERATION
bull Remember a potentiometer has three legs the reference (R) the signal (S) and the ground (G) as shown below 5 volts is supplied to the reference current flows from the reference (R) through the entire resistor to ground (G) The Signal wiper slides across the resistor changing measure voltage as it moves As the wiper moves towards the reference (R) the measured signal voltage at (S) will increase As the wiper moves away from the Reference (R) towards ground (G) the measured signal voltage drops
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
POTENTIOMETER APPLICATIONS
bull Since potentiometer are used to measure changes in position they naturally are used for throttle EGR AC blend door and power seat position sensors All potentiometers have three wires and are used to measure position changes
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
RESISTOR RATING COLOR BANDS
bull The first two bands set the digit or number value of the resistor
bull The third band also known as the multiplier band is the number of zeros added to the number value
bull The last band is the Tolerance band Example +- 10
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
RESISTOR COLOR BAND CHART
bull The chart below is used to interpret the color bands on the carbon resistor Another chart is used to show the value of tolerance band colors
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
READING COLOR BANDS - RATING VALUE
bull The first color band is Green with a value of 5The second color band is Red with a value of 2The third band is Black with a value of 0 zero (No zeros are added)
bull So the resistor has a base value of 52 ohms
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
READING COLOR BANDS - TOLERANCE VALUE
bull Resistors vary in tolerance (accuracy) Common tolerance values are 20 10 5 2 or 1 simply meaning the maximum percent allowable difference the resistor value actually is from the designed value rating A 1 resistor is a higher quality resistor than one with a 20 rating
bull The tolerance band (last band) is silver with a value of 10 So the resistance value is 52 ohms plus or minus 52 ohms (468 to 572 ohms)
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
CAPACITOR
bull A device used to store charge in an electrical circuitbull functions much like a battery but charges and discharges
much more efficiently bull A basic capacitor is made up of two conductors separated by
an insulator or dielectric bull The dielectric can be made of paper plastic mica ceramic
glass a vacuum or nearly any other nonconductive material
Symbol of capacitor
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
CAPACITANCEbull Measure of a capacitors ability to store charge bull A large capacitance means that more charge can be storedbull Measured in farads symbol F bull However 1F is very large bull so prefixes are used to show the smaller values bull Three prefixes (multipliers) are used micro (micro) n (nano) and p
(pico) bull micro means 10-6 (millionth) so 1000000microF = 1F bull n means 10-9 (thousand-millionth) so 1000nF = 1microF bull p means 10-12 (million-millionth) so 1000pF = 1nF
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
TYPES
bull Fixed capacitors
bull Electrolytic capacitorsndash Polarized capacitorsndash Nonpolarized capacitors
raquo Ceramic capacitorsraquo Plastic capacitorsraquo Mica capacitorsraquo Paper capacitors
bull Variable capacitors
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
FIXED CAPACITORS
Electrolytic capacitorsPolarized capacitorbull have implicit polarity bull can only be connected one way
in a circuit bull Symbol
Nonpolarized capacitor
bull has no implicit polarity bull can be connected either way in
a circuit bull Eg Ceramic mica
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
VARIABLE CAPACITORS
bull Mostly used in radio tuning circuits bull Sometimes called ldquo tuning capacitorsrdquobull Have very small capacitance valuesbull Ttypically between 100pF and 500pF (100pF = 00001microF)
Variable Capacitor Symbol
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
DISSIPATION FACTOR
bull Measure of the power factor (or losses) of a capacitor
bull DF = 2 P fRC X 100 where
bull R -- Equivalent Series Resistance (ESR) of the capacitor bull f -- frequency bull C -- capacitance bull Dissipation factor varies with frequency and temperature
bull ESR -- measure of the total lossiness of a capacitor which includes the leads electrodes dielectric losses leakage (IR) and most important the end spray connecting the leads to the
metallized film
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
InductorsInductorsInductor are used in electrical circuits because they store energy in their magnetic fields
What is an Inductor
A coil of wire that can carry current
Energy is stored in the inductor
Current produces a magnetic field
Flux
iCurrent
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
TYPES
bull Fixed inductorsndash Depending on the type of core used
bull Air core inductorsbull Iron core inductorsbull Ferrite core inductors
bull Variable inductors
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
FIXED INDUCTORS
bull Air core inductorsbull Consists of few turns of wire wound
on a hollow former
bull Generally used in radio frequency applications where very low value of inductance is required
bull Iron core inductorsbull Contains a number of turns of
copper wire wound on a hollow former
bull Generally used in low frequency applications such as filter circuits in power supplies or chokes in fluorescent tubes
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
FIXED INDUCTORS (contdhellip)
bull Ferrite core inductors
bull Made up of non-metallic compounds consisting mainly of ferric oxide in combination with one or two bivalent metal oxides
bull Appliocationsraquo rf chokes for supply decoupling purposeraquo Switching regulated type dc power supplies raquo Various types of filters used in communication
equipment
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
VARIABLE INDUCTORS
bull symbol
bull Hollow former has screw threads in the inner hollow portion
bull Similar matching threads are provided on the ferrite core which can be screwed in or out of the former
bull Because of the change of the position of the ferrite core the value of the inductance changes
bull Maximum when ferrite core is fully in
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Q of an Inductor
bull No power loss in an ideal inductorbull But losses do occur in practicalinductorbull 2 types of losses
bull Hysteresis and eddy current losses in the corebull I2R loss
Rs Ls
Equivalent circuit of an Inductor
Q = ω Ls Rs
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
THE BIPOLAR JUNCTION TRANSISTOR
bull The bipolar junction transistor is a 3-terminal device consisting 2 layers of n-type material sandwiching a thin p-type layer or 2 layers of p-type material sandwiching a thin layer of n-type material
bull These structures are appropriately called npn transistor and pnp transistor respectively
bull The terminals are called Emitter Base and Collector
bull The emitter is heavily doped the base is lightly doped and collector is moderately doped
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
TRANSISTOR PHYSICAL STRUCTURE AND SYMBOL
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull There are two types of BJTs the npn and pnpbull The two junctions are termed the base-emitter junction and the base-collector junctionbull The term bipolar refers to the use of both holes and electrons as charge carriers in the transistor structurebull In order for the transistor to operate properly the two junctions must have the correct dc bias voltages ndash the base-emitter (BE) junction is forward biased ndash the base-collector (BC) junction is reverse biased
Forward-Reverse bias of a BJT
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
TRANSISTOR OPERATION
For current to flow through the BJT its two p-n junctions (2 diodes back to back) must be properly biased Typically one junction is forward bias while the other is reverse bias
The figure below shows the biasing of a pnp transistor
Notice that the emitter-base junction is forward biased while the collector-base junction is reverse biased
Majority carriers will flow from emitter to base across the forward biased junction Because the base layer is very thin and has a high resistance (lightly doped) most of these carriers will diffuse across the reverse-biased junction into the collector in the same direction of the minority charges and only tiny amounts of current will flow out of the base terminal Typically collector currents are of the order of mA while base currents are μA Appling Kirchhoffrsquos current law IE = IC + IB
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
TRANSISTOR CURRENTSbull Transistor Currents
IE = IC + IB
bull alpha (αDC)IC = αDCIE
bull beta (βDC)IC = βDCIB
ndash βDC typically has a value between 50 and 500
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull DC voltages for the biased transistorbull Collector voltage
VC = VCC - ICRC
bull Base voltageVB = VE + VBE
ndash for silicon transistors VBE = 07 V
TRANSISTOR VOLTAGES
BJT operating modes
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
OPERATION MODE
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull Active ndash Most importance mode eg for amplifier operationndash The region where current curves are practically
flatbull Saturation
ndash Barrier potential of the junctions cancel each other out causing a virtual short
ndash Ideal transistor behaves like a closed switchbull Cutoff
ndash Current reduced to zerondash Ideal transistor behaves like an open switch
OPERATION MODE
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
BJT - operation in Active mode Active Mode Circuit Model
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
TRANSISTOR CONFIGURATIONS
There are three types Common-Base (CB) Common-Emitter (CE) and Common-Collector (CC)
THE COMMON-BASE CONFIGURATIONThe base is common to both the input and the output usually at ground potential
bull Current Gain lt1bull Power Gaingt1bull Voltage Gaingt1
bull Low ip Impedancebull High op Impedance
Features of CB Connection
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
THE COMMON-EMITTER CONFIGURATION
bull Emitter is common or reference to both input and output signalbull The CE configuration is the one most commonly encountered since it provides both good current and voltage gain for ac signalsbull In the CE configuration the input is between the base and the emitter The output is between the collector and the emitter
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
THE COMMON-COLLECTOR CONFIGURATION OR EMITTER FOLLOWER
bull Collector is common to both input and output Mainly used for current amplification and impedance matchingbull Characteristics curve is same as CE configurationbull A typical transistor power amp will have a CE stage followed by a CC stage
Features of CC Connection
bull High Input Impedance
bull Low Output impedance
bull Voltage Gain lt 1
bull Power + Current Gain
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
1 An equivalent circuit of a NPN transistor is two diodes tied anode to anode one cathode being the emitter the other the collector and the junction of the anodes is the base 2 When a NPN transistor is in operation there is always a constant 06 volt drop between the base and emitter ie the base is always ~ 06 volts more positive than the emitter--always 3 There is no output at the collector until the base has reached ~ 06 volts and the base is drawing current ie any signal that appears at the base that is not up to ~ 06 volts (and not drawing base current) is never seen at the collector 4 The base requires a current not a voltage to control the collector current 5 The collector is a current source it does not source a voltage 6 The collector appears to output a voltage when a resistor is connected between it and power 7 The collector is a high impedance when compared to the emitter
SOME CHARACTERISTICS OF BJTS ndash A RECAP
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
8 The transistor can output an amplified signal either from the collector or the emitter (or both) 9 When operating with a collector resistor (RL) the output voltage from the collector is an amplified voltage 10 When operating with only an emitter resistor (Re) the output voltage from the emitter is not an amplified voltage because it is always ~ 06 volts below the input (base) voltage--hence the name voltage follower But because the emitter can source large amounts of current to the LOAD it can be said there was CURRENT amplification 11 The collector--being high impedance--cannot drive a low impedance load 12 The emitter--being a low impedance--can drive a low impedance load 13 The voltage gain from the collector is greater than one (Gv gt 1) 14 The voltage gain from the emitter is less than one (Gv lt 1) 15 Both the collector and the emitter output ~ the same power E x I = P
SOME CHARACTERISTICS OF BJTS ndash A RECAP
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Silicon Controlled Rectifiers
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Silicon Controlled Rectifier
bull A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a four layer solid state device that controls current flow
bull The name ldquosilicon controlled rectifierrdquo is a trade name for the type of THYRISTOR commercialized at General Electric in 1957
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Silicon Controlled Rectifier bull An SCR can be seen as a conventional rectifier controlled by a
gate signal
bull It is a 4-alternately doped semiconductor layers 3-terminal device 3-leads are referred to as the Anode Cathode and
Gate bull When the gate to cathode voltage exceeds a certain threshold
the device turns on and conducts current
bull Which are used as electronically controlled switches
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Silicon Controlled Rectifier bull The operation of a SCR can be understood in terms of a pair of
tightly coupled Bipolar Junction Transistors
bull used for the purpose of controlling electrical power while
BJTs and FETs Since they do not have the power handling
capability bull SCR has three states
bull Reverse blocking mode forward blocking mode and forward conducting mode
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
TYPES OF DIODES
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
V-I Characteristics of SCR
bull The V-I curve shows the relationship between VF and IF when the SCRs gate is open
bull When a Forward voltage is applied to the SCR
ndash The SCRs cathode-to-anode voltage is designated as VF at this time VF increases from zero the SCR conducts only a small forward current (IF ) which is due to leakage As VF continues to increase IF remains very low and almost constant but eventually a point is reached where IF increases rapidly and VF drops to a low value
ndash The VF value required to trigger this sudden change is referred to as the Forward Breakover Voltage (Vp) When this value of Vp is reached the SCR simply breaks down and conducts a high IF which is limited only by the external resistance in series with the device
ndash The SCR switches from the off state to the on state at this time The drop in VF occurs because the SCR s resistance drops to an extremely low value and most of the source voltage appears across the series resistor
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull When the SCR is in the on state
ndash only a slight increase in VF is required to produce a tremendous increase in IF
ndash the SCR will remain in the on state as long as IF remains at a substantial value Only when IF drops below a certain minimum value will the SCR switch back to its off-state
ndash This minimum value of IF which will hold the SCR in the on state is referred to as the SCRs Holding Current and is usually designated at IH The IH value is located at the point where breakover occurs
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull When a reverse voltage is applied to the SCR
ndash the device functions in basically the same manner as a reverse-biased PN junction diode As the reverse voltage
ndash (VR ) across the SCR increases from zero only a small reverse current (IR) will flow through the device due to leakage This current will remain small until VR becomes large enough to cause the SCR to breakdown Then IR will increase rapidly if VR increases even slightly above the breakdown point
ndash The reverse voltage (VR) required to breakdown the SCR is referred to as the SCRs Reverse Breakdown Voltage
ndash ndash If too much reverse current is allowed to flow through the SCR after
breakdown occurs the device could be permanently damaged
ndash this situation is normally avoided because the SCR is usually subjected to operating voltages which are well below its breakdown rating
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull When the gate is made positive with respect to the cathode
ndash gate current will flow and the SCRs forward characteristics will be affected
ndash The Ig = 0 curve shows the relationship between VF and IF when the gate current is zero
ndash The Ig1 curve is plotted for a specific but relatively low value of gate current Notice that this curve has the same general shape as the Ig = 0 curve but the forward breakover point occurs sooner (at a lower VF value)
ndash The Ig2 curve is plotted for a slightly higher gate current and also has the same general shape as the other two curves However the breakover point occurs even sooner at this higher for different values of gate value of gate current
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Silicon Controlled Rectifier
bull Industrially SCRs are applied to produce DC voltages for motors from AC line voltage
bull Rectifier
ndash Half-wave rectifier full-wave rectifier
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Half-wave rectifier
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Half-wave rectifier
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Half-wave rectifier
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Reviews
bull A SCR is essentially a diode with an extra terminal added
bull This extra terminal is called the gate and it is used to trigger the device into conduction by the application of a small voltage
bull Widely used in applications where dc and ac power must be controlled These devices are often used to apply a specific amount of power to a load or to completely remove it however they are also used to regulate or adjust the amount of
power applied to a specific load
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Application DC Motor Driver
bull DC motor speed generally depends on a combination of the voltage and current flowing in the motor coils and the motor loads or braking torque
bull The speed of the motor is proportional to the voltage and the torque is proportional to the current
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Light Emitting Diodes
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull Light emitting diodes commonly called LEDs are real unsung heroes in the electronics world
bull They form the numbers on digital clocks transmit information from remote controls light up watches and they can form images on a jumbo television screen 0r illuminate traffic light
bull Basically LEDs are just tiny light bulbs that fit easily into an electrical circuit But unlike ordinary incandescent bulbs they dont have a filament that will burn out and they dont get especially hot They are illuminated solely by the movement of electrons in a semiconductor material and they last just as long as a standard transistor
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Inside a LEDbull The two wires extending below the LED epoxy enclosure or the bulb
indicate how the LED should be connected into a circuit bull The negative side of an LED lead is indicated in two ways
ndash by the flat side of the bulbndash by the shorter of the two wires extending from the LED ndash The negative lead should be connected to the negative terminal of a battery
LEDs operate at relative low voltages between about 1 and 4 volts and draw currents between about 10 and 40 milliamperes
ndash Voltages and currents substantially above these values can melt a LED chip
ndash The most important part of a LED is the semi-conductor chip located in the center of the bulb
ndash The chip has two regions separated by a junction The p region is dominated by positive electric charges and the n region is dominated by negative electric charges
ndash The junction acts as a barrier to the flow of electrons between the p and the n regions Only when sufficient voltage is applied to the semi-conductor chip can the current flow and the electrons cross the junction into the p region
ndash In the absence of a large enough electric potential difference (voltage) across the LED leads the junction presents an electric potential barrier to the flow of electrons
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
LED-Electrical Properties-PN junctions
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Operation
bull When the current flows across a diode the negative electrons move one way and positive holes move the other way
bull the holes exist at a lower energy level than the free electrons so when a free electron falls it loses energy
bull this energy emitted in the form of a light photon The size of electronrsquos ldquofallrdquo determines the energy level of the photon which determines its colour A bigger fall produces a photon with the higher energy level and therefore a higher light frequency
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
(Contdhellip)bull PN junction diode in forward bias the electron-hole
recombination leads to photon emission
bull I = Is(eeVkT-1)
bull Threshold voltage Vth = Ege
bull I = IseeVηkT
where η is the ideality factor
Double Heterostructure is used to confine the carriers improving the radiative recombination rate
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
LED-Optical Properties-Efficiency
bull ηint = of photons emitted from active region per second of electrons injected in to LED per second
= Pint (hν) I e bull ηextr = of photons emitted into free space per second of photons emitted from active region per second = P (hν)
Pint (hν)
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
raquoTemperature dependence of emission intensity
bull Emission intensity decreases with increasing temperaturebull Causes include non-radiative recombination via deep levels surface
recombination and carrier loss over heterostucture barriers
raquoHigh internal efficiency LED designs
bull Radiative recombination probability needs to be increased and non-radiative recombination probability needs to be decreased
bull High carrier concentration in the active region achieved through double heterostructure (DH) design improves radiative recombination
R=Bnpbull DH design is used in all high efficiency designs today
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
High internal efficiency designs
bull Doping of the active regions and that of the cladding regions strongly affects internal efficiency
bull Active region should not be heavily doped as it causes carrier spill-over in to the confinement regions decreasing the radiative efficiency
bull Doping levels of 1016-low 1017 are used or none at all
bull P-type doping of the active region is normally done due to the larger electron diffusion length
bull Carrier lifetime depends on the concentration of majority carriers
bull In low excitation regime the radiative carrier lifetime decreases with increasing free carrier concentration
bull Hence efficiency increases with doping
bull At high concentration dopants induce defects acting as recombination centers
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
High extraction efficiency structures
bull Shaping of the LED die is critical to improve their efficiency
bull LEDs of various shapes hemispherical dome inverted cone truncated cones etc have been demonstrated to have better extraction efficiency over conventional designs
bull However cost increases with complexity
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Visible spectrum LEDs
The plot charts the gains made in luminous efficiency till date
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
White-light LEDs
bull White light can be generated in several different ways
bull One way is to mix to complementary colors at a certain power ratio
bull Another way is by the emission of three colors at certain wavelengths and power ratio
bull Most white light emitters use an LED emitting at short wavelength and a wavelength converter
bull The converter material absorbs some or all the light emitted by the LED and re-emits at a longer wavelength
bull Two parameters that are important in the generation of white light are luminous efficiency and color rendering index
bull It is shown that white light sources employing two monochromatic complementary colors result in highest possible luminous efficiency
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
White-light LEDs( Contdhellip)
bull Wavelength converter materials include phosphors semiconductors and dyes
bull The parameters of interest are absorption wavelength emission wavelength and quantum efficiency
bull The overall energy efficiency is given by
η = ηext(λ1 λ2)
bull Even if the external quantum efficiency is 1 there is always an energy loss associated with conversion
bull Common wavelength converters are phosphors which consist of an inorganic host material doped with an optically active element
bull The optically active dopant is a rare earth element oxide or another compound
bull Common rare earth elements used are Ce Nd Er and Th
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
White-light LEDs
bull Phosphors are stable materials and can have quantum efficiencies of close to 100
bull Dyes also can have quantum efficiencies of close to 100
bull Dyes can be encapsulated in epoxy or in optically transparent polymers
bull However organic dyes have finite lifetime They become optically inactive after 104-106 optical transitions
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
LED Advantages
bull While all diodes release light most dont do it very effectively
bull In an ordinary diode the semiconductor material itself ends up absorbing a lot of the light energy LEDs are specially constructed to release a large number of photons outward
bull Additionally they are housed in a plastic bulb that concentrates the light in a particular direction
bull Most of the light from the diode bounces off the sides of the bulb traveling on through the rounded end
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull Remote control operation (Advantages of LED)
bull the basic operation of the remote goes like this You press a button When you do that you complete a specific connection The chip senses that connection and knows what button you pressed It produces a morse-code-line signal specific to that button The transistors amplify the signal and send them to the LED which translates the signal into infrared light The sensor in the TV can see the infrared light and seeing the signal reacts appropriately
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
RECTIFIERS
bullINTRODUCTION
bullHALF WAVE RECTIFIERS
bullFULL WAVE RECTIFIERS
bullBRIDGE RECTIFIERS
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull Rectification is the conversion of alternating current (AC) to direct current (DC)
bull A rectifier converts a sinusoidal voltage to a constant voltage
bull This involves a device that only allows one-way flow of electrons
bull As we have seen this is exactly what a semiconductor diode does bull A Diode switches polarity from + to - many times a second into a straight DC supply
bull Rectifier is a type of ac-dc converterbull1048707 Single phasebull1048707 Three phase
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
HALF WAVE RECTIFIERS
bull A half-wave rectifier is a circuit that allows only one half-cycle of the AC voltage waveform to be applied to the load resulting in one non-alternating polarity across it
bull The resulting DC delivered to the load ldquopulsatesrdquo significantly
bull This circuit takes an AC signal in and chops off anything that falls below 0 Volts
bull The half-wave rectifier is used in AM radios to rectify the signal
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
CIRCUIT DIAGRAM
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
OUTPUT WAVEFORM
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bullThe Half wave rectifier is a circuit which converts an ac voltage to dc voltage
bullIn the Half wave rectifier circuit the transformer serves two purposes
bullIt can be used to obtain the desired level of dc voltage (using step up or step down transformers)
bullIt provides isolation from the power line
bullThe primary of the transformer is connected to ac supply
bullThis induces an ac voltage across the secondary of the transformer
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode
bull As a result a current IL flows through the load resistor RL
bull The forward biased diode offers a very low resistance and hence the voltage drop across it is very small
bull Thus the voltage appearing across the load is practically the same as the input voltage at every instant
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed
bull As a result the diode is reverse biased
bull Practically no current flows through the circuit and almost no voltage is developed across the resistor
bull All input voltage appears across the diode itself
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bullThus when the input voltage is going through its positive half cycle output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load
bullThis explains the unidirectional pulsating dc waveform obtained as output
bull The process of removing one half the input signal to establish a dc level is aptly called half wave rectification
bullThe diode only conducts on every other half cycle
bullThere is one pulse for every cycle in ie 50 pulses per second (in the UK)
bullThe rectified voltage is DC (it is always positive in value)However it is not a steady DC but PULSATING DC
bullIt needs to be smoothed before it becomes useful
bullIf the diode is reversed then the output voltage is negative
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Signal In
Signal Out (Half-wave)
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
The simplest rectifier uses one diode like this
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
PARAMETERS
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Peak Inverse Voltage
bull When the input voltage reaches its maximum value Vm during the negative half cycle the voltage across the diode is also maximum
bull This maximum voltage is known as the peak inverse voltage
bull Thus for a half wave rectifier
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Ripple Factor
bull Ripple factor is defined as the ratio of RMS value of ac component to the dc component in the output
bull RMS voltage at the load resistance
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull In half wave rectifier the rated voltage of the transformer secondary is
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull But actually the RMS current flowing through the winding is only
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Form Factor
bull Form factor is given by
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Peak Factor
bull Peak factor is given by
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
FULL WAVE RECTIFIERSbull A full-wave rectifier is a circuit that converts both half-cycles of
the AC voltage waveform to an unbroken series of voltage pulses of the same polarity
bull The resulting DC delivered to the load doesnt ldquopulsaterdquo as much
bull A full-wave rectifier flips the negative half of the signal up into the positive range
bull When used in a power supply the full-wave rectifier allows us to convert almost all the incoming AC power to DC
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
OUTPUT WAVEFORM
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull A Full Wave Rectifier is a circuit which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage
bull It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage
bull During the positive half cycle of the input voltage diode D1 becomes forward biased and D2 becomes reverse biased
bull Hence D1 conducts and D2 remains OFF
bull The load current flows through D1 and the voltage drop across RL will be equal to the input voltage
bull During the negative half cycle of the input voltage diode D1 becomes reverse biased and D2 becomes forward biased
bull Hence D1 remains OFF and D2 conducts
bull The load current flows through D2 and the voltage drop across RL will be equal to the input voltage
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
CURRENT FLOW DURING ONE HALF CYCLE
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
PARAMETERS
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Ripple Factor
The ripple factor for a Full Wave Rectifier is given by
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
RMS value of the voltage at the load resistance is
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Efficiency
bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Full Wave Rectifier is 812
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Transformer Utilization Factor
bull Transformer Utilization Factor TUF can be used to determine the rating of a transformer secondary
bull It is determined by considering the primary and the secondary winding separately and it gives a value of 0693
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Form Factor
bull Form factor is defined as the ratio of the rms value of the output voltage to the average value of the output voltage
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Peak Factor
bull Peak factor is defined as the ratio of the peak value of the output voltage to the RMS value of the output voltage
bull Peak inverse voltage for Full Wave Rectifier is 2Vm because the entire secondary voltage appears across the non-conducting diode
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
BRIDGE RECTIFIERSbull The Bridge rectifier is a circuit which converts an ac voltage to
dc voltage using both half cycles of the input ac voltagebull A bridge rectifier can be made using four individual diodesbull It is called a full-wave rectifier because it uses all the AC wave
(both positive and negative sections) bull 14V is used up in the bridge rectifier because each diode
uses 07V when conducting and there are always two diodes conducting
bull Bridge rectifiers are rated by the maximum current they can pass and the maximum reverse voltage they can withstand (this must be at least three times the supply RMS voltage so the rectifier can withstand the peak voltages)
bull One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
CIRCUIT FOR A BRIDGE RECTIFIER
Alternate pairs of diodes conduct changing over the connections so the alternating directions of AC are converted to the one direction of DC
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
OUTPUT OF A BRIDGE RECTIFIER
Output full-wave varying DC(using all the AC wave)
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
WORKING PRINCIPLEbull The circuit has four diodes
connected to form a bridge bull The ac input voltage is applied
to the diagonally opposite ends of the bridge
bull The load resistance is connected between the other two ends of the bridge
bull For the positive half cycle of the input ac voltage diodes D1 and D3 conduct whereas diodes D2 and D4 remain in the OFF state
bull The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
bull For the negative half cycle of the input ac voltage diodes D2 and D4 conduct whereas D1 and D3 remain OFF
bull The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle
bull Thus a bi-directional wave is converted into a unidirectional wave
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
PARAMETERS
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Peak Inverse Voltage
bull Peak inverse voltage represents the maximum voltage that the non- conducting diode must withstand
bull At the instance the secondary voltage reaches its positive peak value Vm the diodes D1 and D3 are conducting where as D2 and D4 are reverse biased and are non-conducting
bull The conducting diodes D1 and D3 have almost zero resistance
bull Thus the entire voltage Vm appears across the load resistor RL The reverse voltage across the non-conducting diodes D2 (D4) is also Vm
bull Thus for a Bridge rectifier the peak inverse voltage is given by PIV = VM
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Ripple Factorbull The ripple factor for a Bridge Rectifier
is given by
bull RMS value of the voltage at the load resistance is
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-
Efficiency bull Efficiency h is the ratio of the dc output power to ac input power
bull The maximum efficiency of a Bridge Rectifier is 812
- RESISTORS
- TYPES
- FIXED RESISTORS
- CARBON RESISTORS
- WIRE-WOUND RESISTORS
- VARIABLE RESISTORS
- RHEOSTAT
- RHEOSTAT OPERATION
- POTENTIOMETER
- POTENTIOMETER OPERATION
- POTENTIOMETER APPLICATIONS
- RESISTOR RATING COLOR BANDS
- RESISTOR COLOR BAND CHART
- READING COLOR BANDS - RATING VALUE
- READING COLOR BANDS - TOLERANCE VALUE
- CAPACITOR
- CAPACITANCE
- TYPES
- FIXED CAPACITORS
- VARIABLE CAPACITORS
- DISSIPATION FACTOR
- Slide 22
- Slide 23
- FIXED INDUCTORS
- FIXED INDUCTORS (contdhellip)
- VARIABLE INDUCTORS
- Q of an Inductor
- THE BIPOLAR JUNCTION TRANSISTOR
- Slide 29
- Slide 30
- TRANSISTOR OPERATION
- Slide 32
- Slide 33
- OPERATION MODE
- Slide 35
- Slide 36
- Slide 37
- Slide 38
- TRANSISTOR CONFIGURATIONS
- Slide 40
- Slide 41
- Slide 42
- Slide 43
- Silicon Controlled Rectifiers
- Silicon Controlled Rectifier
- Slide 46
- Slide 47
- TYPES OF DIODES
- V-I Characteristics of SCR
- Slide 50
- Slide 51
- Slide 52
- Slide 53
- Silicon Controlled Rectifier
- Half-wave rectifier
- Slide 56
- Slide 57
- Reviews
- Application DC Motor Driver
- Light Emitting Diodes
- Slide 61
- Slide 62
- Slide 63
- LED-Electrical Properties-PN junctions
- Operation
- Slide 66
- LED-Optical Properties-Efficiency
- Slide 68
- High internal efficiency designs
- High extraction efficiency structures
- Visible spectrum LEDs
- White-light LEDs
- White-light LEDs( Contdhellip)
- Slide 74
- LED Advantages
- Slide 76
- RECTIFIERS
- Slide 78
- HALF WAVE RECTIFIERS
- CIRCUIT DIAGRAM
- OUTPUT WAVEFORM
- WORKING PRINCIPLE OF THE HALF WAVE RECTIFIER
- Slide 83
- Slide 84
- Slide 85
- Slide 86
- Slide 87
- Slide 88
- PARAMETERS
- Peak Inverse Voltage
- Ripple Factor
- Efficiency
- Transformer Utilization Factor
- Slide 94
- Form Factor
- Peak Factor
- FULL WAVE RECTIFIERS
- CIRCUIT DIAGRAM OF A FULL WAVE RECTIFIER
- Slide 99
- Slide 100
- WORKING PRINCIPLE OF A FULL WAVE RECTIFIER
- Slide 102
- CURRENT FLOW DURING ONE HALF CYCLE
- Slide 104
- Slide 105
- Slide 106
- Efficiency
- Slide 108
- Slide 109
- Slide 110
- BRIDGE RECTIFIERS
- CIRCUIT FOR A BRIDGE RECTIFIER
- OUTPUT OF A BRIDGE RECTIFIER
- WORKING PRINCIPLE
- Slide 115
- Slide 116
- Peak Inverse Voltage
- Slide 118
- Slide 119
-