power assign

8/3/2019 Power Assign

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Power

Electronics

Assignment Abhinav Sinha

09415



BATTERY CHARGER

A battery charger is a device used to put energy into a secondary cell or rechargeable

battery by forcing an electric current through it. The charge current depends upon the

technology and capacity of the battery being charged.

A simple charger works by supplying a constant DC or pulsed DC power source to a battery being

charged. The simple charger does not alter its output based on time or the charge on the battery.

This simplicity means that a simple charger is inexpensive, but there is a tradeoff in quality. Typically,

a simple charger takes longer to charge a battery to prevent severe over-charging. Even so, a battery

left in a simple charger for too long will be weakened or destroyed due to over-charging. These

chargers can supply either a constant voltage or a constant current to the battery.

Simple AC-powered battery chargers have much higher ripple current and ripple voltage than other

kinds of battery supplies. When the ripple current is within the battery-manufacturer-recommended

level, the ripple voltage will also be well within the recommended level. The maximum ripple current

for a typical 12 V 100 Ah VRLA battery is 5 amps. As long as the ripple current is not excessive (more

than 3 to 4 times the battery-manufacturer-recommended level), the expected life of a ripple-

charged VRLA battery is within 3% of the life of a constant DC-charged battery.

Fig: a battery charger circuit



Types of battery chargers

1. Trickle

2. Timer-based

3. Intelligent

4. Universal battery charger –analyzers

5. Fast

6. Pulse

7. Inductive

8. USB-based

9. Solar chargers

Charge rate is often denoted as C or C-rate and signifies a charge or discharge rate equal to the

capacity of a battery in one hour.[14]

For a 1.6Ah battery, C = 1.6A. A charge rate of C /2 = 0.8A would

need two hours, and a charge rate of 2C = 3.2A would need 30 minutes to fully charge the battery

from an empty state, if supported by the battery. This also assumes that the battery is 100% efficient

at absorbing the charge.

Applications

Mobile phone charger

Battery charger for vehicles

Battery electric vehicle



Fig : reed relay coupled ssr

Transformer-Coupled SSR's (see figure 2), in which the control signal is applied (through a DC-AC

converter, if it is DC, or directly, if It is AC) to the primary of a small, low-power transformer, and the

secondary voltage that results from the primary excitation is used (with or without rectification,amplification, or other modification) to trigger the thyristor switch. In this type, the degree of input-

output isolation depends on the design of the transformer.

Photo-coupled SSR's (see figure 3), in which the control signal is applied to a light or infrared source

(usually, a light-emitting diode, or LED), and the radiation from that source is detected in a

photosensitive semi-conductor (i.e., a photosensitive diode, a photo-sensitive transistor, or a photo-

sensitive thyristor). The output of the photo-sensitive device is then used to trigger (gate) the TRIAC

or the SCR's that switch the load current. Clearly, the only significant “coupling path” between input

and output is the beam of light or infrared radiation, and electrical isolation is excellent. These SSR's

are also referred to as “optically coupled” or “photo-isolated”.



The relay is characterised by a number of parameters including the required activating input voltage,

current, and whether it is AC or DC; the output voltage and current and whether it is AC or DC,

voltage drop or resistance affecting output current, thermal resistance, and thermal and electrical

parameters for safe operating area (e.g., derating according to thermal resistance when repeatedly

switching large currents).

Advantages over mechanical relays

Most of the relative advantages of solid state and electromechanical relays are common to

all solid-state as against electromechanical devices.

SSRs are faster than electromechanical relays; their switching time is dependent on the time

needed to power the LED on and off, of the order of microseconds to milliseconds

Lower (if any) minimum output current (latching current) required

Increased lifetime, particularly if activated many times, as there are no moving parts to wear

o Output resistance remains constant regardless of amount of use

Clean, bounceless operation

Decreased electrical noise when switching

No sparking, allowing use in explosive environments where it is critical that no spark is

generated during switching

Totally silent operation

Inherently smaller than a mechanical relay of similar specification (if desired may have the

same "casing" form factor for interchangeability).

Much less sensitive to storage and operating environment factors such as mechanical shock,

vibration, humidity, and external magnetic fields.

Disadvantages

Voltage/current characteristic of semiconductor rather than mechanical contacts:

o When closed, higher resistance (generating heat), and increased electrical

noise

o When open, lower resistance, and reverse leakage current (typically µA

range)

o Voltage/current characteristic is not linear (not purely resistive), distorting

switched waveforms to some extent. An electromechanical relay has the low

ohmic (linear) resistance of the associated mechanical switch when activated,

and the exceedingly high resistance of the air gap and insulating materialswhen open.

o DC load must observe polarity (- and + not interchangeable) to avoid an

undesirable "always conducting" state that does not depend on switching

input. Electromechanical relays do not depend on polarity.

Possibility of spurious switching due to voltage transients (due to much faster

switching than mechanical relay)

Isolated bias supply required for gate charge circuit

Higher Transient Reverse Recovery time (Trr) due to the presence of Body diode

More Likely to fail in the "Closed" state compared to Electromechanical relays which

are more likely to fail in the "Open" State



Static Switches

Since the SCR and the triac are bistable devices, one of their broad areas of application is inthe realm of signal and power switching. This application note describes circuits in which

these thyristors are used to perform simple switching functions of a general type that might

also be performed non-statically by various mechanical and electromechanical switches. In

these applications, the thyristors are used to open or close a circuit completely, as opposed

to applications in which they are used to control the magnitude of average voltage or

energy being delivered to a load.

Statc switch merely connects a load to supply. Static switch does not change or control the

power delivered to load as it is done in single phase voltage controller. In static switches,

the semiconductor switches are turned on at zero-crossing of load current, where as it si not

so in single-phase voltage controller.

Static switches can also be used for latching, current and voltage detection, time delay

circuits, transducer etc.

Static switches are of two types :

1. AC switches

2. Dc switches

If input is AC then ac SS are used ,and for dc input dc SS are used. Switching speed for ac

switches is governed by the supply frequency and turn off time of thyristor. For dc switches,

the switching speed depends on commutation circuitry and turn off time of fast thyristor. Acswitches may be single phase or three phase.

Fig 1: triac static switch



The circuit shown in Figure 1 provides random (anywhere in half-cycle), fast turn-on (<10 μs)

of AC power loads and is ideal for applications with a high-duty cycle. It eliminates

completely the contact sticking, bounce, and wear associated with conventional

electromechanical relays, contactors, and so on. As a substitute for control relays, thyristors

can overcome the differential problem; that is, the spread in current or voltage between

pickup and dropout because thyristors effectively drop out every half cycle. Also, providing

resistor R1 is chosen correctly, the circuits are operable over a much wider voltage range

than is a comparable relay. Resistor R1 is provided to limit gate current (IGTM) peaks. Its

resistance plus any contact resistance (RC) of the control device and load resistance (RL)

should be just greater than the peak supply voltage divided by the peak gate current rating

of the triac. If R1 is set too high, the triacs may not trigger at the beginning of each cycle,

and phase control of the load will result with consequent loss of load voltage and waveform

distortion. For inductive loads, an RC snubber circuit, as shown in Figure 1, is required.

However, a snubber circuit is not required when an alternistor is used.

ADVANTAGES OF STATIC SWITCHES:

1. On time of static switches is of order of 3 us, it has therefore very high switching

speed

2. SS has no moving parts, its maintenance is therefore every low.

3. SS has no bouncing at the time of turning ON.

4. SS has long operational life.

Uninterruptible Power Supply (UPS):

An uninterruptible power supply, also uninterruptible power source, UPS or

battery/flywheel backup, is an electrical apparatus that provides emergency power to a

load when the input power source, typically mains power, fails. A UPS differs from an

auxiliary or emergency power system or standby generator in that it will provide

instantaneous or near-instantaneous protection from input power interruptions by means

of one or more attached batteries and associated electronic circuitry for low power users,

and or by means of diesel generators and flywheels for high power users. The on-battery

runtime of most uninterruptible power sources is relatively short—5 –15 minutes being

typical for smaller units—but sufficient to allow time to bring an auxiliary power source on

line, or to properly shut down the protected equipment.

While not limited to protecting any particular type of equipment, a UPS is typically used to

protect computers, data centers, telecommunication equipment or other electrical

equipment where an unexpected power disruption could cause injuries, fatalities, serious

business disruption or data loss. UPS units range in size from units designed to protect a

single computer without a video monitor (around 200 VA rating) to large units powering

entire data centers, buildings, or even cities.[1]



The primary role of any UPS is to provide short-term power when the input power source

fails. However, most UPS units are also capable in varying degrees of correcting common

utility power problems:

1. Power failure: defined as a total loss of input voltage.

2. Surge: defined as a momentary or sustained increase in the main voltage.

3. Sag: defined as a momentary or sustained reduction in input voltage.

4. Spikes, defined as a brief high voltage excursion.

5. Noise, defined as a high frequency transient or oscillation, usually injected into the

line by nearby equipment.6. Frequency instability: defined as temporary changes in the mains frequency.

7. Harmonic distortion: defined as a departure from the ideal sinusoidal waveform

expected on the line.

FIG: UPS

The circuit drawn pertains to a regular industrial UPS (Uninterruptible Power Supply), which

shows how the batteries take control during an outage in electrical supply or variation

beyond the normal limits of the voltage line, without disruption on the operation providing

a steady regulated output (5 Volts by LM7805) and an unregulated supply (12 Volts).

The input to the primary winding of the transformer (TR1) is 240V. The secondary winding

can be raised up to 15 Volts if the value is at least 12 Volts running 2 amp. The fuse (FS1)

acts as a mini circuit breaker for protection against short circuits, or a defective battery cell

in fact. The presence of electricity will cause the LED 1 to light. The light of LED will set off

upon power outage and the UPS battery will take over

The circuit was designed to offer more flexible pattern wherein it can be customized by

using different regulators and batteries to produce regulated and unregulated voltages.

Utilizing two 12 Volt batteries in series and a positive input 7815 regulator, can control a15V supply.



LIGHT DIMMER

Dimmers are devices used to vary the brightness of a light. By decreasing or increasing the RMS

voltage and, hence, the mean power to the lamp, it is possible to vary the intensity of the light

output. Although variable-voltage devices are used for various purposes, the term dimmer is

generally reserved for those intended to control resistive incandescent, halogen and more recently

compact fluorescent (CFL) lighting. More specialized equipment is needed to dim fluorescent,

mercury vapor, solid state and other arc lighting.

Types of dimmer

1. Saltwater dimmer

2. Coil-rotation transformer

3. Rheostat dimmer

4. Autotransformer dimmer

5. Thyristor dimmer

How Dimmer Switches Work

The Old Way Early dimmer switches had a pretty straightforward solution to adjusting light levels -- a variabl

resistor. An ordinary resistor is a piece of material that doesn't conduct electrical current well -- it

offers a lot of resistance to moving electrical charge. A variable resistor consists of a piece of

resistive material, a stationary contact arm and a moving contact arm.

In this design, you vary the total resistance of the resistor by adjusting the distance that the

charge has to travel through resistive material. If the contact arm is to the left, charge

flowing through the circuit only has to travel through a little bit of resistive material. If the

contact arm is all the way to the right, the charge has to move through more resistive

material.



As the charge works to move through the resistor, energy is lost in the form of heat. When

you put a resistor in a series circuit, the resistor's energy consumption causes a voltage drop

in the circuit, decreasing the energy available to other loads (the light bulb, for example).

Decreased voltage across the light bulb reduces its light output.

The problem with this solution is that you end up using a lot of energy to heat the resistor,

which doesn't help you light up the room but still costs you. In addition to be being

inefficient, these switches tend to be cumbersome and potentially dangerous, since the

variable resistor releases a substantial amount of heat.

Modern dimmer switches take a more efficient approach, as we'll see in the next section.

The New and Improved Way

Instead of diverting energy from the light bulb into a resistor, modern resistors rapidly shut

the light circuit off and on to reduce the total amount of energy flowing through the circuit.

The light bulb circuit is switched off many times every second.The switching cycle is built around the fluctuation of household alternating current (AC). AC

current has varying voltage polarity -- in an undulating sine wave, it fluctuates from a

positive voltage to a negative voltage. To put it another way, the moving charge that makes

up AC current is constantly changing direction. In the United States, it goes through one

cycle (moving one way, then the other) 60 times a second. The diagram below shows this

sixtieth-of-a-second cycle.

A modern dimmer switch "chops up" the sine wave. It automatically shuts the light bulb

circuit off every time the current reverses direction -- that is, whenever there is zero voltage

running through the circuit. This happens twice per cycle, or 120 times a second. It turns the

light circuit back on when the voltage climbs back up to a certain level.

This "turn-on value" is based on the position of the dimmer switch's knob or slider. If the

dimmer is turned to a brighter setting, it will switch on very quickly after cutting off. The

circuit is turned on for most of the cycle, so it supplies more energy per second to the light

bulb. If the dimmer is set for lower light, it will wait until later in the cycle to turn back on.

That's the basic concept, but how does the dimmer actually do all of this? In the next couple

of sections, we'll look at the simple

When there is "normal" voltage across the terminals and little voltage on the gate, the triac

will act as an open switch -- it won't conduct electricity. This is because the electrons from

the N-type material fill in holes along the border with the P-type material, creating

depletion zones, insulated areas where there are few free electrons or holes (see this pagefor a full explanation of depletion zones).

http://electronics.howstuffworks.com/led1.htm

http://electronics.howstuffworks.com/led1.htm



If you apply a strong enough voltage to the gate, it will disrupt the depletion zones so

electrons can move across the triac. The exact sequence varies depending on the direction

of the current -- that is, which part of the AC cycle you're in. Let's say the current is flowing

so the top terminal is negatively charged and bottom terminal is positively charged. The

circuit is arranged so that the voltage boost on the gate will have the same charge as the top

terminal. So we get something that looks like this:

When the gate is "charged," the voltage difference between the gate and the lower terminal

is strong enough to get electrons moving between them. Moving electrons out of the N-type

material -- area e -- disrupts the depletion zone between areas e and d. Introducing more

free electrons into area d disrupts the depletion zone between d and c. Electrons from area

c can move toward the bottom terminal, jumping from hole to hole in area d. This

introduces more holes into area c, which gets electrons moving out of the depletion zone

between c and b. The voltage is strong enough to drive electrons from area a into the holes

in area b, disrupting the last depletion zone. With the depletion zones dispersed, electrons

can move freely from the top terminal to the bottom terminal -- the triac is now conductive!

(Note: Some dimmer switches also contain a similar semiconductor device called a diac, inaddition to a triac. These circuits work in the same basic way.)

In order for the triac to start conducting electricity between its two terminals, it needs a

voltage boost on its gate. The required voltage level doesn't change, but you can adjust how

long it takes the gate to "charge up" to this voltage. This is where the variable resistor and

the firing capacitor come in.

Current passes through the variable resistor and charges the firing capacitor (current builds

up electrical charge on the capacitor's plates -- see How Capacitors Work for more

information). When the capacitor builds up a certain amount of charge, it has the necessary

voltage to conduct current from the gate to the bottom terminal. It discharges, making the

triac conductive.

Turning the dimmer switch knob pivots the contact arm (or contact plate) on the variable

resistor, increasing or decreasing its total resistance. When the knob is set to "dim," thevariable resistor offers greater resistance so it "holds up" the current. As a result, the

necessary boost voltage doesn't build up as quickly on the firing capacitor. By the time the

capacitor is charged enough to make the triac conductive, the AC current cycle is well

underway. If you turn the knob the other way, the variable resistor offers less resistance and

the capacitor gets up to the necessary boost voltage earlier in the fluctuating cycle.

As soon as the current fluctuates back to the zero voltage point, there is nothing driving

current through the triac, so the electrons stop moving. The depletion zones form again,

and the triac loses its conductivity until the boost voltage builds up on the gate.

s



References

http://home.howstuffworks.com/dimmer-switch2.htm

http://en.wikipedia.org/wiki/

http://www.electronic-circuits-diagrams.com/

http://www.Circuitstoday.com

http://josepino.com/

http://www.circuitstoday.com

http://www.circuit-projects.com


http://en.wikipedia.org/wiki/Dimmer


http://www.circuitstoday.com/www.circuitstoday.com


http://www.circuitstoday.com/

http://www.circuitstoday.com/


http://www.circuitstoday.com/www.circuitstoday.com


http://en.wikipedia.org/wiki/Dimmer


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