topic 1(power supply unit)
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Topic 1
Power supply unit
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COURSE LEARNING OUTCOMES
(CLO)
CLO1. explain correctly the principles of electronic
circuits by using block diagram or circuit diagram (C4 -Analysis)
CLO2. conduct the construction of electronic circuits
application during practical works based on the theory
and principle operation of the circuits. (P4 - Mechanics)
CLO3. deliver an oral presentation to display goodcommunication skills. (A2Response to phenomena)
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LEARNING OUTCOMES
Upon completion of this topic students should be able to:
Explain the operation of a DC power supply circuit1.1
Explain applications of rectifiers1.2
1.3
1.4
1.5
Explain applications of filter
Explain applications about voltage regulator
Explain applications about voltage divider
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Power Supply
All electronic circuits need a power source towork.
For electronic circuits made up of transistorsand/or ICs, this power source must be a DCvoltage of a specific value.
A battery is a common DC voltage source forsome types of electronic equipmentespecially portables like cell phones andiPods.
Most non-portable equipment uses powersupplies that operate from the AC power linebut produce one or more DC outputs.
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Power supply unit
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Power supply unit
The functionsof power supply unit is
to convert the signal form AC input
power to DC power.A power supplyunit built with five major parts:
transformer, rectifier, filter, regulator
and voltage divider.
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Block diagram of dc power
supply
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Function of each block
TransformerReduce the value of the input acvoltage.
RectifierA circuit that converts ac voltage to dc
voltage
FilterThe main task of filter is to convert the
voltage at pulse to the voltage rippled
RegulatorVoltage regulator circuit is used to
reduced the difference to zero Voltage dividerCircuit is needed in power
supplies for electronic equipment requires.
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Output waveform from each block
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Transformer
Built from two winding transformer primary
and secondary loops. Network is to
separate the secondary circuit of the ac
supply lines high. This isolation canprevent a user from the secondary ac
voltage electric shock high. Separation of
the primary circuit is able to avoid theeffects of damage received in the
secondary winding circuit.
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Transformer
Transformer has a primary winding and
secondary winding. The ratio of the
number of turns in the primary to the
secondary number of turns is thetransformer turns ratio.
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Transformer
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Transformer
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Voltage ratio is proportional to the voltage induced in
the primary to the secondary winding turns.
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Transformer
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When the number of secondary winding
turns slightly compared to primary, lower
secondary voltage from the voltage in the
primary. Secondary voltage can becalculated.
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Transformer
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Function of Transformer
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Question
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Solution
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Diode
What is the
function of diode?
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Functions of diode
Switch
Clipper
Rectifier Clamp
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Schematic diagram and physical
structure of a diode
2.1 Understand the Characteristics ofdiode as a semiconductor
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OPERATION DIODE DURING
FORWARD & REVERSE BIASED
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APPLICATIONS OF DIODE
1. RECTIFIER
Rectifier is the circuit that used one or more diode to
convert the AC voltage to the pulsating dc voltage
There is 3 type of rectifiers :-
i) Half wave rectifier
ii) Full wave rectifieriii)Bridge rectifier
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Half-wave rectifier
Half-wave rectifier
Output Voltage
Input Supply Voltage
Operation
During the positive circle of input supply, diode D is in forward
biased and act as close switch. So the current can flow through it. ,
producing an output voltage as shown above.During the negative circle of the input supply, diode is reverse
bias and act as open switch, so the current cant flow through diode.
No voltage appears at output.
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How Rectifiers Work
The simplest form of rectifier isthe half wave rectifier shown.
Only the transformer, rectifierdiode, and load (RL) are shownwithout the filter and othercomponents.
The half wave rectifier produces
one sine pulse for each cycle ofthe input sine wave.
When the sine wave goespositive, the anode of the diodegoes positive causing the diodeto be forward biased. The diode
conducts and acts like a closedswitch letting the positive pulseof the sine wave to appearacross the load resistor.
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How Rectifiers Work (continued)
When the sine wave goesnegative, the diode anode will
be negative so the diode will bereverse biased and no currentwill flow.
No negative voltage will appearacross the load. The load
voltage will be zero during thetime of the negative half cycle.
See the waveforms that showthe positive pulses across theload. These pulses need to beconverted to a constant DC.
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Question
A half-wave rectifier circuit to the input
voltage 20 Vp-p, 50 Hz. Assuming no
voltage drop across the diode, calculate: -
i) the output signal voltage rectifier
ii) the output signal frequency
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Solution
Vm = 20 Vp-p
= 10 Vp
then VK = 10 Vp
Output signal frequency = Frequency of the input signal
= 50 Hz
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Full-wave rectifier
A full-wave rectifier converts the whole of the input waveformto one of constant polarity (positive or negative) at its output.
Full-wave rectification converts both polarities of the input
waveform to DC (direct current), and is more efficient.
For single-phase AC, if the transformer is center-tapped, then two
diodes back-to-back (i.e. anodes-to-anode or cathode-to-cathode)
can form a full-wave rectifier..
VV
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The average (av) and root-mean-square (rms) output voltages
of an ideal single phase full wave rectifier can be calculatedas:
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Full Wave Rectifier
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Consider the first half-cycle, when the source voltage polarity
is positive (+) on top and negative (-) on bottom. At this time,
only the top diode is conducting; the bottom diode is blocking
current, producing only positive half-cycle of the input supplyappears at load as shown at the above figure
R
Input supply Output voltage
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During the next half-cycle, the AC polarity reverses. Now, the
other diode (bottom) and the other half of the transformer'ssecondary winding carry current to the load resistor, producing
the same polarity of voltage as before (Figure below)
R
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2.2 Know diode
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Full-wave rectifier bridge rectifier
applications as rectifiers
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During positive half-cycle
D1
D3
D1 and D3 conduct, allowing the current
flowing to the load, RL. Load voltage appears at
load as shown at above figure.
RL
Load voltage
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During negative half-cycle
D2
D4
Load Voltage
D2 and D4 conduct, allowing the current
flowing to the load, RL. Load voltage appears at
load as shown at above figure.
RL
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Question
A full-wave rectifier circuit to the input
voltage 20 Vp-p 50 Hz. Used transformer
has a turns ratio 2:1. Assuming no voltage
drop across the diode, calculate: -
i) the output signal voltage rectifier
ii) the output signal frequency
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Solution
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Bridge Rectifier
Another widely used rectifier isthe bridge rectifier. It uses four
diodes. This is called a full wave rectifier
as it produces an output pulsefor each half cycle of the inputsine wave.
On the positive half cycle of theinput sine wave, diodes D1 andD2 are forward biased so act asclosed switches appearing inseries with the load.
On the negative half cycle,
diode D1 and D2 are reversebiased and diodes D3 and D4are forward biased so currentflows through the load in thesame direction.
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FILTER
The main task of the filter is to convert the
voltage pulse to a.t. rippling. The best filter
circuit is a filter that can reduce as much
as possible the value of Vr pp dc voltageproduced by rippling.
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H th Filt W k
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How the Filter Works
A large capacitor is connectedacross the load resistor. This
capacitor filters the pulses into amore constant DC.
When the diode conducts, thecapacitor charges up to thepeak of the sine wave.
Then when the sine voltage
drops, the charge on thecapacitor remains. Since thecapacitor is large it forms a longtime constant with the loadresistor. The capacitor slowlydischarges into the loadmaintaining a more constant
output. The next positive pulse comes
along recharging the capacitorand the process continues.
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Ripple
The capacitor does a good job of smoothing thepulses from the rectifier into a more constant DC.
A small variation occurs in the DC because thecapacitor discharges a small amount between the
positive and negative pulses. Then it recharges.This variation is called ripple.
The ripple can be reduced further by making thecapacitor larger.
The ripple appears to be a sawtooth shaped ACvariation riding on the DC output.
A small amount of ripple can be tolerated in somecircuits but the lower the better overall.
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Ripple voltage
The output of rectifier circuit is the
pulsating DC voltage .The resulting
pulsating dc signal smooth the output
voltage, we used filter circuit. Figure belowshows the output wave before and after
the filter circuit.
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Ripple voltage
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Types of filter
There are 4 main types of filter:-
i)Filter capacitor
i) Resistor capacitor (RC filter)
ii) Inductance capacitor (LC filter)
iii) type filter
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RC filter diagram
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RC filter
Is an electric circuit composed of resistors
and capacitors driven by voltage or
current source
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Operation of RC filter
When a circuit consists of only a charge
capacitor and a resistor. The capacitor will
discharge its stored energy through the
resistor. The voltage across the capacitorcan be found by kirchoffs current law.
Where the current through the capacitor
must equal the current through theresistor.
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LC filter
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LC filter
LC filter can also called resonant circuit.
The purpose of LC is to oscillate with
minimal damping. When connected
together, they can act as an electricalresonator, an electrical analogue of a
tuning fork, storing electrical energy
oscillating at the circuit's resonantfrequency.
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Operation of LC filter
A capacitor stores energy in the electric
fieldbetween its plates, depending on the
voltage across it, and an inductor stores
energy in its magnetic field, depending onthe currentthrough it.
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Operation of LC filter
If a charged capacitor is connected across
an inductor, charge will start to flow
through the inductor, building up a
magnetic field around it and reducing thevoltage on the capacitor. Eventually all the
charge on the capacitor will be gone and
the voltage across it will reach zero.However, the current will continue,
because inductors resist changes in
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filter
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filter
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Combination C and LC filter
PI-TYPE FILTERS use both capacitive
and inductive filters connected in a pi-type
configuration. Because of the combinationof filtering devices, the ability of the pi filter
to remove ripple voltage is superior to that
of either the capacitance or inductancefilter
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The Regulator
Most regulators are ICs . These are feedback control circuits that
actually monitor the output voltage to detectvariations.
If the output varies, for whatever reason, theregulator circuit automatically adjusts theoutput back to the set value.
Regulators hold the output to the desiredvalue.
Since ripple represents changes in theoutput, the regulator also compensates forthese variations producing a near constant
DC output.
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Voltage regulator circuit
The power supply means the output
changes when the input supply or the load
resistance also changes. The main
purpose of voltage regulator is to decreasethe changes to zero(0) or at least to the
minima value.
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Voltage regulator circuit
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Voltage regulator circuit
There are three (3) voltage regulator
circuit normally used :-
a. Zener diode voltage regulator
b. Series transistor voltage regulator
c. Integrated circuits voltage regulator
(LM7805)
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Zener diode voltage regulator
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Operation
Zener diode will functions as voltage
regulator when reversed biased.Zener
diode has their own advantages, can be
regulate their voltage when it is operate atthe zener region. To operate, the input
voltage must higher than zener voltage
and the load resistance not effect thezener diode is zero.
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Series transistor voltage regulator
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Operation
Connect the transistor serial with load and
it will control the input voltage value to
output.If the output voltage decreases ,the
increases VBE will cause the transistor toproduce more current value will make the
output voltage increases and make the
output voltage constant.
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Operation
Zener diode as a refer voltage .It is same
process if the output voltage increases.
Transistor will decrease the current value ,
cause the output voltage decrease and theoutput voltage become constant.
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Integrated circuits voltage regulator
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g g g
(LM7805)
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Operation
The serial LM 78XX(where XX=
05,06,08,10,12,15,18 or 24).It is 3
terminal voltage regulator .IC LM 7805 will
produce the output voltage +5V .LM 7806will produce the 6V output voltage. LM
7824 will produce +24V output voltage.
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Voltage divider circuit
In electronic devices system, especially
big or complicated .It is contains several
circuit level, sometime use DC voltage
which are different value. For example TVsystem have more than 10 circuit level
,different function and some of the need
DC voltage,100V,48V,12V and so on.
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Voltage divider circuit
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POWER SUPPLY CIRCUIT
Figure below shows a power supply
complete circuit.From left to right,we found
the center tap transformer will decrease
the AC supply voltage .Then full rectifierwaveform change AC voltage to DC
voltage.filter are used to straighten pulse
at the voltage and it will stabilize by zenerdiode voltage divider.
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POWER SUPPLY CIRCUIT
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Example
Based on figure below, name and explain
briefly circuit in part A dan part B,
If part A is changed to Bridge Rectifier,
re-draw the complete circuit for power
supply unit.
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Example
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Solution
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Solution
voltage supply ,M terminal becomeve ,Gwill zero potential(grounded) and N
become +ve.D2 diode will forward biased
while D1 will reverse biased. Current willflow along N, D2, C, A, B, G. Current flow
through RLduring the +ve cycle is similar
when ve cycle, we will got the similarshape of wave too.
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Solution
The direction of current flow through RLduring +ve cycle = the direction of current
flow through RLwhenve cycle. When we
connect the oscilloscope across RL, wewill know the shape of the output voltage
is similar
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Solution
Part BZener Diode Voltage Regulator
The operation;-
Zener diode will functions as voltage regulator
when reversed biased.Zener diode has theirown advantages, can be regulate their voltage
when it is operate at the zener region. To
operate, the input voltage must higher than
zener voltage and the load resistance not effectthe zener diode is zero
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Solution
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THE END
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THE END