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AUTO RESET OVER OR UNDER VOLTAGE CUTOUT

A

MINI PROJECT REPORT

Su b m i t t e d t o t h e Fa c u l t y o f En g i n e e r i n g o f

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY,

KAKINADA.

In p a r t i a l f u l fi ll m e n t o f t h e r e q u i r e m e n t s f o r t h e a w a r d o f d e g r e e o f

BACHELOR OF TECHNOLOGYIn

ELECTRONICS & COMMUNICATION ENGINEERINGSUBMITTED BY

K.SAIKRISHNA (09R81A0444) K.N.V.S RAMANJANEYULU (09R81A0445)

CH.SIVARAMI REDDY (08R81A0498) P.CHARAN TEJA (09R81A0452).

UNDER T HE ESTEEMED GUIDENCE OF

V.MOHANA KRISHNA, B tech

ASST.PROFESSOR.

DEPARTMENT OFELECTRONICS&COMMUNICATIONENGINEERINGSRI SUNFLOWERCOLLEGEOFENGINEERING&TECHNOLOGY

LANKAPALLI(2009-2013).

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AUTO RESET OVER OR UNDER VOLTAGE CUTOUT

A

MINI PROJECT REPORT

Su b m i t t e d t o t h e Fa c u l t y o f En g i n e e r i n g o f

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY,

KAKINADA.

In p a r t i a l f u l fi ll m e n t o f t h e r e q u i r e m e n t s f o r t h e a w a r d o f d e g r e e o f

BACHELOR OF TECHNOLOGYIn

ELECTRONICS & COMMUNICATION ENGINEERINGSUBMITTED BY

K.SAIKRISHNA (09R81A0444) K.N.V.S RAMANJANEYULU (09R81A0445)

CH.SIVARAMI REDDY (08R81A0498) P.CHARAN TEJA (09R81A0452).

UNDER T HE ESTEEMED GUIDENCE OF

V.MOHANA KRISHNA, B tech

ASST.PROFESSOR.

DEPARTMENT OFELECTRONICS&COMMUNICATIONENGINEERINGSRI SUNFLOWERCOLLEGEOFENGINEERING&TECHNOLOGY

LANKAPALLI (2009-2013).

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SRI SUNFLOWERCOLLEGE OF ENGINEERING &TECHNOLOGY

LANKAPALLI(CHALLAPALLI)

Departmentof Electronics &CommunicationEngineering

CERTIFICATE

This is to certify that the project title AUTO RESET OVER OR UNDER

VOLTAGE CUTOUT is a bonafied record of work done jointly byK.SAI KRISHNA (0 9 R8 1 A0 4 4 4 )

K.N.V.S RAMANJANEYULU (0 9 R8 1 A0 4 4 5 )

CH.SIVARAMI REDDY (0 8 R8 1 A0 4 9 8 )

P.CHARAN TEJA (0 9 R8 1 A0 4 5 2 )

Under my guidance and superv is ion and is submit t ed i n part ia l fu l f i l lm ent of t he

requir ement s for t he award of th e degree of bachelor of Technol ogy in Elect ron ics &

Comm unicat i on Engineer in g by Jawahar la l Nehru Technological Uni vers i ty dur ing th eacademic year 2013.

V.MOHANA KRISHNA B TECH Y.R.K.PARAMAHAMSA M T E C H

Project Guide Head Of The Department, E.C.E

EXTERNAL EXAMINER

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ABSTRACT

This over/under voltage cut-out will save your costly electrical and electronic appliances

from the adverse effects of very high and very low mains voltages. The circuit features auto

reset and utilizes easily available components. It makes use of the comparators available

inside 555 timer ICs. Supply is tapped from different points of the power supply circuit for

relay and control circuit operation to achieve reliability.

The circuit utilises comparator 2for control while comparator 1 output (connected to reset pin

R) is kept low by shorting pins 5 and 6 of 555 IC. The positive input pin of comparator 2 is

at 1/3rd of Vcc voltage. Thus as long as negative input pin 2 is less positive than 1/3 Vcc,

comparator 2 output is high and the internal flip-flop is set ,i.e. its Q output (pin 3) is high. At

the same time pin 7 is in high impedance state and LED connected to pin7 is therefore off.The output (at pin 3) reverses (goes low) when pin2 is taken more positive than1/3 Vcc. At

the same time pin7 goes low (as Q output of internal flip-flop is high) and the ED connected

to pin 7is lit. Both timers (IC1 andIC2) are configured to function in the same fashion. Preset

VR1 is adjusted for under voltage (say 160 volts) cut-out by observing that LED1 just lights

up when mains voltage is slightly greater than160V AC. At this setting the output at pin 3 of

IC1 is low and transistor T1 is in cut-off state. As a result RESET pin4 of IC2 is held high

since it is connected to Vcc via 100 kilo-ohm resistor R4.Preset VR2 is adjusted for

overvoltage (say 270V AC) cut-out by observing that LED2 just extinguishes when

the mains voltage is slightly less than 270V AC. With RESET pin 4 of IC2 high, the output

pin 3 is also high. As a result transistor T2conducts and energises relay RL1, connecting load

to power supply via its N/O contacts.

This is the situation as long as mains voltage is greater than 160V AC but less than 270V AC.

When mains voltage goes beyond270V AC, it causes output pin 3 ofIC2 to go low and cut-

off transistor T2and de- energise relay RL1, in spite of RESET pin 4 still being high. When

mains voltage goes below 160V AC, IC1s pin 3 goes high and LED1 is extinguished. The

high output at pin 3results in conduction of transistor T1.As a result collector of transistor

T1as also RESET pin 4 of IC2 are pulled low. Thus output of IC2 goes low and transistor T2

does not conduct. As a result relay RL1 is de-energised, which causes load to be disconnected

from the supply. When mains voltage again goes beyond 160V AC (but less than 270V AC)

the relay again energises to connect the load to power supply.

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LIST OF FIGURES :-

s/no Name page no.

1 Circuit Diagram.

2 Pin Diagram of 555IC.....

3 Circuit diagram of transformer

4 The ideal transformer as a circuit element..

5 Sketch of auto transformer

6 Sketch of leakage transformer..

7 Sketch of instrument transformer

8 Electronic symbols of diodes..

9 Electronic symbols of capacitors

10 Symbol of IC 7809...

11 Symbol of resistor

12 Symbol of rheostat

13 Symbol of potentiometer..

14 IEC style resistor symbol.

15 Operational diagram of resistor..

16 Circuit diagram of series resistor

17 Circuit diagram of parallel resistor18 Band description of resistors...

19 Symbol of 555IC

20 Internal block diagram of 555IC.

21 Pin diagram of 555IC

22 Basic symbol of relay.

23 Symbol of PNP transistor..

24 Symbol of NPN transistor.

25 Transistor as a switch

26 Transistor as an amplifier.

27 Electronic symbol of an LED

28 Types of LEDS..

29 Symbol of a comparator

30 Types of FLIP.FLOPS..

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LIST OF FIGURES:

s/no Name page no.

1 Color coding of a resistor

2 Color coding of a capacitor..

3 Pin description of 555IC

4 Transistor colors and materials

5 Operation of an SR LATCH.

6 Truth table of SR NAND LATCH

7 Truth table of SR LATCH

8 Truth table of JK LATCH

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INDEX

CHAPTER 1 INTRODUCTION

1.1 INTRODUCTION.

CHAPTER 2 CIRCUIT DIAGRAM

2.1 CIRCUIT DIAGRAM.

2.2 DESCRIPTION OF THE CIRCUIT DIAGRAM

CHAPTER 3 TRANSFORMER

3.1 BASIC PRINCIPLE OF TRANSFORMER..

3.2 INDUCTION LAW

3.3 IDEAL POWER EQUATION

3.4 TYPES OF TRANSFORMER

3.4.1 POLYPHASE TRANSFORMERS.

3.4.2 LEAKAGE TRANSFORMERS.

3.4.3 AUDIO TRANSFORMERS...

3.4.4 OUTPUT TRANSFORMERS.

3.4.5 INSTRUMENT TRANSFORMERS

3.4.6 CURRENT TRANSFORMERS..

CHAPTER 4 DIODES

4.1 SEMICONDUCTOR DIODES..

4.1.1 DIODE..

4.1.2 LIGHT EMITTING DIODE.

4.1.3 PHOTO DIODE

4.1.4 TRANSCIENT VOLTAGE SUPRESSION DIODE

4.2 ELECTRONIC SYMBOL OF DIODE

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CHAPTER 5 CAPACITORS

5.1 CURRENT-VOLTAGE RELATION..

5.2 CAPACITOR COLOR CODING

CHAPTER 6 IC 7809

6.1 SYMBOL OF IC 7809

6.2 DECRIPTION OF THE SYMBOL.

CHAPTER 7 RESISTOR

7.1DEFINITION OF A RESISTOR

7.2ELECTRONIC SYMBOLS AND NOTATION

7.2.1 RHEOSTAT.

7.2.2 POTENTIOMETER

7.2.3 IEC STYLE POTENTIOMETER

7.3THEORY OF OPERATION

7.4 OHMS LAW

7.5 SERIES AND PARALLEL RESISTORS..

7.6 POWER DESSIPATION..

7.7 RESISTOR COLOR CODING.

CHAPTER 8 555 IC

8.1 INTEGRATED CIRCUIT

8.2 TIMER

8.3 INTERNAL BLOCK DIAGRAM OF 555 IC.

8.4 DESCRIPTION OF INTERNAL BLOCK IAGRAM..

8.5 PINDIAGRAM AND ITS DESCRIPTION

8.6 MODES OF 555 IC..

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8.6.1 MONOSTABLE......

8.6.2 ASTABLE.

CHAPTER 9 RELAY

9.1 DEFINITION OF A RELAY

9.2 BASIC DESCRIPTION AND OPERATION OF A RELAY..

CHAPTER 10 TRANSISTORS

10.1 TRANSISTOR AS A SWITCH

10.2 TRANSISTOR AS AN AMPLIFIER

10.3 BIPOLAR JUNCTION TRANSISTOR.

CHAPTER 11 LIGHT EMITTING DIODE

11.1 ELECTRONIC SYMBOL OF AN LED

11.2 CONSTRUCTION OF AN LED

11.3 TYPES OF AN LED

11.4 COLORS AND MATERIALS OF AN LED

CHAPTER 12 COMPARATORS

12.1 INPUT VOLTAGE RANGE

12.2 OP-AMP VOLTAGE COMPARATOR........

CHAPTER 13 FLIP FLOPS

13.1 TYPES OF FLIP FLOPS..

13.2 SIMPLE SET-RESET LATCHES.

13.2.1 SR NOR LATCH..

13.2.2 SR NAND LATCH

13.2.3 JK LATCH..

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CHAPTER 14 ADVANTAGES

CHAPTER 15 APPLICATIONS

CHAPTER 16 RESULT

CHAPTER 17 SCOPE FOR FUTURE WORK

CHAPTER 18 CONCLUSION

CHAPTER 19 REFERENCES

CHAPTER 20 BIBILOGRAPHY

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CHAPTER-I

INTRODUCTION

Here is an inexpensive auto cut-off circuit, which is fabricated using transistor and other

discrete components. It can be used to protect loads such as refrigerator, T.V., and VCR from

undesirable over and under line voltages, as well as surges caused due to sudden

failure/resumption of main power supply. This circuit can be used directly as a standalone

circuit between the mains supply and the load, or it may be inserted between an existing

automatic/manual stabilizer and the load.

The over/under voltage cut-off with ON-Time delay provides various types of protection

1) Over-voltage protection.

2) Under-voltage protection.

3) Protection against transients.

4) Protection to load from frequent turning ON & OFF by providing time delay.

The on-time delay circuit not only protects the load from switching surges but also from

quick changeover (off and on) effect of over/under-voltage relay, in case the mains voltage

starts fluctuating in the vicinity of under or over voltage preset points. When the mains

supply goes out of preset (over or under voltage) limits, the relay/load is turned off

immediately and it is turned on only when A.C. mains voltage settles within the presets limits

for a period equal to the on time delay period. The on-time delay period is preset able for 5

seconds to 2 minutes duration using presets VR3 and VR4. For refrigerators the delay should

be preset for about 2 minutes duration to protect the compressor motor from frequently

turning on and off.

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CIRCUIT DIAGRAM

The circuit features auto reset and utilizes easily available components. It makes use of the

comparators available inside 555 timer ICs. Supply is tapped from different points of the

power supply circuit for relay and control circuit operation to achieve reliability. Below is the

circuit diagram:

This over/under voltage cut-out will save your costly electrical and electronic appliances

from the adverse effects of very high and very low mains voltages. The circuit features auto

reset and utilises easily available components. It makes use of the comparators available inside

555 timer ICs. Supply is tapped from different points of the power supply circuit for relay

and control circuit operation to achieve reliability.

When mains voltage goes beyond 270V AC, it causes output pin 3 of IC2 to go low

and cut-off transistor T2 and de-energies relay RL1, in spite o RESET pin 4 still being high.

When mains voltage goes below 160V AC, IC1s pin 3 goes high and LED1 is extinguished.The high output at pin 3 results in conduction of transistor T1. As a result collector of

transistor T1 as also RESET pin 4 of IC2 are pulled low. Thus output of IC2 goes low and

transistor T2 does not conduct. As a result relay RL1 is de-energized, which causes load to be

disconnected from the supply. When mains voltage again goes beyond 160V AC (but less

than 270V AC) the relay again energizes to connect the load to power supply.

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DESCRIPTION OF CIRCUIT DIAGRAM

The circuit utilizes comparator 2 for control while comparator 1 output (connected to

reset pin R) is kept low by shorting pins 5 and 6 of 555 IC. The positive input pin of

comparator 2 is at 1/3rd of Vcc voltage. Thus as long as negative input pin 2 is less positive

than 1/3 Vcc, comparator 2 output is high and the internal flip-flop is set, i.e. its Q output (pin

3) is high. At the same time pin 7 is in high impedance state and LED connected to pin 7 is

therefore off. The output (at pin 3) reverses (goes low) when pin 2 is taken more positive than

1/3 Vcc. At the same time pin 7 goes low (as Q output of internal flip-flop is high) and the

ED connected to pin 7 is lit.

Both timers (IC1 and IC2) are configured to function in the same fashion. Preset VR1

is adjusted for under voltage (say 160 volts) cut-out by observing that LED1 just lights up

when mains voltage is slightly greater than 160V AC. At this setting the output at pin 3 of

IC1 is low and transistor T1 is in cut-off state. As a result RESET pin 4 of IC2 is held high

since it is connected to Vcc via 100 kilo-ohm resistor R4. Preset VR2 is adjusted for over

voltage (say 270V AC) cut-out by observing that LED2 just extinguishes when the mains

voltage is slightly less than 270V AC. With RESET pin 4 of IC2 high, the output pin 3 is also

high. As a result transistor T2 conducts and energizes relay RL1, connecting load to power

supply via its N/O contacts. This is the situation as long as mains voltage is greater than 160V

AC but less than 270V AC.

When mains voltage goes beyond 270V AC, it causes output pin 3 of IC2 to go low

and cut-off transistor T2 and de-energies relay RL1, in spite o RESET pin 4 still being high.

When mains voltage goes below 160V AC, IC1s pin 3 goes high and LED1 is extinguished.The high output at pin 3 results in conduction of transistor T1. As a result collector of

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transistor T1 as also RESET pin 4 of IC2 are pulled low. Thus output of IC2 goes low and

transistor T2 does not conduct. As a result relay RL1 is de-energized, which causes load to be

disconnected from the supply. When mains voltage again goes beyond 160V AC (but less

than 270V AC) the relay again energizes to connect the load to power supply.

CHAPTER-IV

DESCRIPTION OF COMPONENTS

4.1 TRANSFORMER:

A transformer is a power converter that transfers energy between two electrical circuits by

inductive coupling between two or more windings. A varying current in the primary winding

creates a varying magnetic flux in the transformer's core and thus a varying magnetic flux

through the secondary winding. This varying magnetic flux induces a varying EMF, or

VOLTAGE, in the secondary winding. This effect is called inductive coupling.

If a load is connected to the secondary winding, current will flow in this winding, and

electrical energy will be transferred from the primary circuit through the transformer to the

load. Transformers may be used for AC-to-AC conversion of a single power frequency, or for

conversion of signal power over a wide range of frequencies, such as audio or radio

frequencies.

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In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to

the primary voltage (Vp) and is given by the ratio of the number of turns in the secondary (Ns)

to the number of turns in the primary (Np) as follows:

By appropriate selection of the ratio of turns, a transformer thus enables an altering

current(AC) voltage to be "stepped up" by makingNs greater than Np, or "stepped down" by

making Ns less than Np. The windings are coils wound around a ferromagnetic core and air-

core transformers being a notable exception.

Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage

microphone to huge units weighing hundreds of tons used in power stations, or to

interconnect portions of power grids. All operate on the same basic principles, although the

range of designs is wide. While new technologies have eliminated the need for transformers

in some electronic circuits, transformers are still found in nearly all electronic devices

designed for house hold voltages. Transformers are essential for high-voltage electric power

transmission, which makes long-distance transmission economically practical.

4.1.1 BASIC PRINCIPLE OF TRANSFORMER:

The transformer is based on two principles: first, that an electric current can produce a

magnetic flux and second that a changing magnetic field within a coil of wire induces a

voltage across the ends of the coil. Changing the current in the primary coil changes the

magnetic flux that is developed. The changing magnetic flux induces a voltage in the

secondary coil.

An ideal transformer is shown in the adjacent figure. Current passing through the primary

coil creates a magnetic field. The primary and secondary coils are wrapped around a core of

very high magnetic permeability such as iron so that most of the magnetic flux passes

through both the primary and secondary coils. If a load is connected to the secondary

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winding, the load current and voltage will be in the directions indicated, given the primary

current and voltage in the directions indicated.

Induction law

The voltage induced across the secondary coil may be calculated from faradays laws of

induction which states that:

where Vs is the instantaneous voltage,Ns is the number of turns in the secondary coil and

is the magnetic flux through one turn of the coil. If the turns of the coil are oriented

perpendicularly to the magnetic field lines, the flux is the product of the magnetic flux

density B and the area A through which it cuts. The area is constant, being equal to the

cross-sectional area of the transformer core, whereas the magnetic field varies with time

according to the excitation of the primary. Since the same magnetic flux passes through

both the primary and secondary coils in an ideal transformer. the instantaneous voltage

across the primary winding equals

Taking the ratio of the two equations forVs and Vp gives the basic equation for stepping up

or stepping down the voltage

Np/Ns is known as the turns ratio, and is the primary functional characteristic of any

transformer. In the case of step-up transformers, this may sometimes be stated as the

reciprocal, Ns/Np. Turns ratio is commonly expressed as an irreducible fraction or ratio: for

example, a transformer with primary and secondary windings of, respectively, 100 and

150 turns is said to have a turns ratio of 2:3 rather than 0.667 or 100:150.

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Ideal power equation

The ideal transformer as a circuit element

If the secondary coil is attached to a load that allows current to flow, electrical power is

transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is

perfectly efficient. All the incoming energy is transformed from the primary circuit to the

magnetic field and into the secondary circuit. If this condition is met, the input electric power

must equal the output power:

giving the ideal transformer equation

This formula is a reasonable approximation for most commercial built transformers today.

If the voltage is increased, then the current is decreased by the same factor. The impedance in

one circuit is transformed by the square of the turns ratio. For example, if an impedance Zs is

attached across the terminals of the secondary coil, it appears to the primary circuit to have an

impedance of (Np/Ns)2Zs. This relationship is reciprocal, so that the impedance Zp of the

primary circuit appears to the secondary to be (Ns/ Np)2Zp.

http://en.wikipedia.org/wiki/File:Transformer_under_load.svghttp://en.wikipedia.org/wiki/File:Transformer_under_load.svg

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TYPES

A wide variety of transformer designs are used for different applications, though they share

several common features. Important common transformer types are described below.

Autotransformer:

In an autotransformer portions of the same winding act as both the primary and secondary.

The winding has at least three taps where electrical connections are made. An

autotransformer can be smaller, lighter and cheaper than a standard dual-winding

transformer, but it does not provide electrical isolation.

As an example of the material saving an autotransformer can provide, consider a double

wound 2 kVA transformer designed to convert 240 volts to 120 volts. Such a transformer

would require 8 amp wire for the 240 volt primary and 16 amp wire for the secondary. If

constructed as an autotransformer, the output is a simple tap at the centre of the 240 volt

winding. Even though the whole winding can be wound with 8 amp wire, 16 amps can

nevertheless be drawn from the 120 volt tap.

Autotransformers are often used to step up or down between voltages in the 110-117-120 volt

range and voltages in the 220-230-240 volt range, e.g., to output either 110 or 120V (with

taps) from 230V input, allowing equipment from a 100 or 120V region to be used in a 230V

region.

A variable autotransformer is made by exposing part of the winding coils and making the

secondary connection through a sliding brush, giving a variable turns ratio. Such a device is

http://en.wikipedia.org/wiki/File:Variable_Transformer_01.jpghttp://en.wikipedia.org/wiki/File:Variable_Transformer_01.jpghttp://en.wikipedia.org/wiki/Brush_(electric)http://en.wikipedia.org/wiki/Tap_(transformer)http://en.wikipedia.org/wiki/Secondary_windinghttp://en.wikipedia.org/wiki/Primary_winding

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often referred to by the trademark name Variac. It resembles, but is different from,

a potentiometer.

Polyphase transformers

For three-phase supplies, a bank of three individual single-phase transformers can be used, or

all three phases can be incorporated as a single three-phase transformer. In this case, the

magnetic circuits are connected together, the core thus containing a three-phase flow of flux.

A number ofwinding configurations are possible, giving rise to different attributes and phase

shifts. One particular polyphase configuration is the zigzag transformer, used

for grounding and in the suppression of harmonic currents.

Leakage transformers

A leakage transformer, also called a stray-field transformer, has a significantly higher leakage

inductance than other transformers, sometimes increased by a magnetic bypass or shunt in its

core between primary and secondary, which is sometimes adjustable with a set screw. This

provides a transformer with an inherent current limitation due to the loose coupling between

its primary and the secondary windings. The output and input currents are low enough to

prevent thermal overload under all load conditionseven if the secondary is shorted.

A resonant transformer is a kind of leakage transformer. It uses the leakage inductance of its

secondary windings in combination with external capacitors, to create one or more resonant

circuits. Resonant transformers such as the Tesla coil can generate very high voltages, and are

able to provide much higher current than electrostatic high-voltage generation machines such

http://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Zigzag_transformerhttp://en.wikipedia.org/wiki/Ground_(electricity)http://en.wikipedia.org/wiki/Harmonichttp://en.wikipedia.org/wiki/File:Kvglr.jpghttp://en.wikipedia.org/wiki/File:Kvglr.jpghttp://en.wikipedia.org/wiki/Electrical_resonancehttp://en.wikipedia.org/wiki/Leakage_inductancehttp://en.wikipedia.org/wiki/Resonant_circuithttp://en.wikipedia.org/wiki/Tesla_coilhttp://en.wikipedia.org/wiki/File:Kvglr.jpghttp://en.wikipedia.org/wiki/Tesla_coilhttp://en.wikipedia.org/wiki/Resonant_circuithttp://en.wikipedia.org/wiki/Resonant_circuithttp://en.wikipedia.org/wiki/Leakage_inductancehttp://en.wikipedia.org/wiki/Electrical_resonancehttp://en.wikipedia.org/wiki/Leakage_inductancehttp://en.wikipedia.org/wiki/Leakage_inductancehttp://en.wikipedia.org/wiki/Harmonichttp://en.wikipedia.org/wiki/Ground_(electricity)http://en.wikipedia.org/wiki/Zigzag_transformerhttp://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Phase_(waves)http://en.wikipedia.org/wiki/Three-phasehttp://en.wikipedia.org/wiki/Potentiometerhttp://en.wikipedia.org/wiki/Variac

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as the Van de Graf generator. One of the applications of the resonant transformer is for

the CCFL inverter.

AUDIO TRANSFORMERS

Audio transformers are those specifically designed for use in audio circuits. They can be used

to block radio frequency interference or the DC component of an audio signal, to split or

combine audio signals, or to provide impedance matching between high and low impedance

circuits, such as between a high impedance tube (valve) amplifier output and a low

impedance loudspeaker, or between a high impedance instrument output and the low

impedance input of a mixing console.

OUTPUT TRANSFORMERS

Early audio amplifiers used transformers for coupling between stages, i.e., for transferring

signal without connecting different operating voltages together. It was realised that

transformers introduced distortion; furthermore they produced significant frequency-

dependent phase shifts, particularly at higher frequencies. The phase shift was not

problematical in itself, but made it difficult to introduce distortion-cancelling negative

feedback, either over a transformer-coupled stage or the whole amplifier. Where they were

used as a convenient way to isolate stages while coupling signals, transformers could be

eliminated by using capacitor coupling.

The transformer coupling the output of the amplifier to the loudspeaker, however, had the

important requirement to couple the high impedance of the output valves with the low

impedance of the loudspeakers. With the 1940s Williamson amplifier as a much-quoted early

example, audio amplifiers with hitherto unprecedentedly low distortion were produced, using

designs with only one transformer, the output transformer, and large overall negative

feedback. Some attempts to design transformer less amplifiers were made, for example using

very-low-impedance power triodes , but were not widely used.

The design of output transformers became a critical requirement for achieving low distortion,

and carefully designed, expensive components were produced with minimal inherent

distortion and phase shift. Blumlein's Ultra-Linear transformer design was used in

http://en.wikipedia.org/wiki/Valve_amplifierhttp://en.wikipedia.org/wiki/Loudspeakerhttp://en.wikipedia.org/wiki/Mixing_consolehttp://en.wikipedia.org/wiki/Phase_shifthttp://en.wikipedia.org/wiki/Distortionhttp://en.wikipedia.org/wiki/Negative_feedbackhttp://en.wikipedia.org/wiki/Distortionhttp://en.wikipedia.org/wiki/Negative_feedbackhttp://en.wikipedia.org/wiki/Negative_feedbackhttp://en.wikipedia.org/wiki/Capacitive_couplinghttp://en.wikipedia.org/wiki/Williamson_amplifierhttp://en.wikipedia.org/wiki/Triodehttp://en.wikipedia.org/wiki/Triodehttp://en.wikipedia.org/wiki/Alan_Blumleinhttp://en.wikipedia.org/wiki/Ultra-Linearhttp://en.wikipedia.org/wiki/Ultra-Linearhttp://en.wikipedia.org/wiki/Alan_Blumleinhttp://en.wikipedia.org/wiki/Triodehttp://en.wikipedia.org/wiki/Williamson_amplifierhttp://en.wikipedia.org/wiki/Loudspeakerhttp://en.wikipedia.org/wiki/Capacitive_couplinghttp://en.wikipedia.org/wiki/Negative_feedbackhttp://en.wikipedia.org/wiki/Negative_feedbackhttp://en.wikipedia.org/wiki/Distortionhttp://en.wikipedia.org/wiki/Phase_shifthttp://en.wikipedia.org/wiki/Coupling_(electronics)http://en.wikipedia.org/wiki/Mixing_consolehttp://en.wikipedia.org/wiki/Loudspeakerhttp://en.wikipedia.org/wiki/Valve_amplifierhttp://en.wikipedia.org/wiki/CCFL_inverterhttp://en.wikipedia.org/wiki/Van_de_Graaff_generator

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conjunction with Williamson's principles, allowing pentode or beam tetrode output devices to

produce the higher power of apentode than a triode, and lower distortion than either type.

Some early junction transistor amplifiers used transformers in the signal path, both interstage

and output, but solid-state designs were rapidly produced with suitably low impedance to

drive loudspeakers without using transformers, allowing very large amounts of feedback to

be applied without instability.

INSTRUMENT TRANSFORMERS

Instrument transformers are used for measuring voltage and current in electrical power

systems, and for power system protection and control. Where a voltage or current is too large

to be conveniently used by an instrument, it can be scaled down to a standardized low value.

Instrument transformers isolate measurement, protection and control circuitry from the high

currents or voltages present on the circuits being measured or controller.

CURRENT TRANSFORMERS:

A current transformeris a transformer designed to provide a current in its secondary coil

proportional to the current flowing in its primary coil.

Voltage transformers (VTs), also referred to as "potential transformers" (PTs), are designed

to have an accurately known transformation ratio in both magnitude and phase, over a range

of measuring circuit impedances. A voltage transformer is intended to present a negligible

load to the supply being measured. The low secondary voltage allows protective relay

equipment and measuring instruments to be operated at a lower voltages.

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Both current and voltage instrument transformers are designed to have predictable

characteristics on overloads. Proper operation of over-current protective relays requires that

current transformers provide a predictable transformation ratio even during a short-circuit.

4.2 DIODES

In electronics, a diode is a two-terminal electronic component with an asymmetric transfer

characteristic, with low resistance to current flow in one direction, and high resistance in the

other. A semiconductor diode, the most common type today, is a crystalline pieceof semiconductor material with a p-n junction connected to two electrical

terminals. A vacuum tube diode is a vacuum tube with two electrodes, a plate and heated

cathode.

The most common function of a diode is to allow an electric current to pass in one direction,

while blocking current in the opposite direction . Thus, the diode can be viewed as an

electronic version of a check valve. This unidirectional behavior is called rectification, and isused to convert alternating current to direct current, including extraction of modulation from

radio signals in radio receiversthese diodes are forms of rectifiers.

However, diodes can have more complicated behavior than this simple onoff action.

Semiconductor diodes begin conducting electricity only if a certain threshold voltage or cut-

in voltage is present in the forward direction. The voltage drop across a forward-biased diode

varies only a little with the current, and is a function of temperature; this effect can be used as

a temperature sensor or voltage reference.

Semiconductor diodes nonlinear currentvoltage characteristic can be tailored by varying

the semiconductor materials and doping, introducing impurities into the materials. These are

exploited in special-purpose diodes that perform many different functions. For example,

diodes are used to regulate voltage, to protect circuits from high voltage surges, to

electronically tune radio and TV receivers, to generate radio frequency oscillations, Gunn

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diodes, IMPATT diodes and to produce light. Tunnel diodes exhibit negative resistance,

which makes them useful in some types of circuits.

Diodes were the first semiconductor electronic devices. The discovery of crystalsrectifying abilities was made by German physicist Ferdinand Braun in 1874. The first

semiconductor diodes, called cat's whisker diodes, developed around 1906, were made of

mineral crystals such as galena. Today most diodes are made of silicon, but

other semiconductors such as germanium are sometimes used.

SEMICONDUCTOR DIODES

Electronic symbols:

The symbol used for a semiconductor diode in a circuit diagram specifies the type of diode.

There are alternate symbols for some types of diodes, though the differences are minor.

DIODE

Light Emitting Diode (LED)

Photodiode

Transient Voltage Suppression (TVS)

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4.3 CAPACITOR

A capacitor is a passive two-terminal electrical component used to store energy in

an electric field. The forms of practical capacitors vary widely, but all contain at least

two electrical conductors separated by a dielectric.

When there is a potential difference across the conductors, a static electric

field develops across the dielectric, causing positive charge to collect on one plate and

negative charge on the other plate. Energy is stored in the electrostatic field. An ideal

capacitor is characterized by a single constant value, capacitance, measured in farads.

This is the ratio of the electric charge on each conductor to the potential difference

between them.

The capacitance is greatest when there is a narrow separation between large areas of

conductor, hence capacitor conductors are often called plates, referring to an early

means of construction. In practice, the dielectric between the plates passes a small

amount of leakage current and also has an electric field strength limit, resulting in

a breakdown voltage, while the conductors and leads introduce an

undesired inductance and resistance.

Capacitors are widely used in electronic circuits for blocking direct current while

allowing alternating current to pass, in filter networks, for smoothing the output

of power supplies, in the resonant circuits that tune radios to particular frequencies, in

electric power transmission systems for stabilizing voltage and power flow, and for

many other purposes.

Current-voltage relation

The current i(t) through any component in an electric circuit is defined as the rate of

flow of a charge q(t) passing through it, but actual charges, electrons, cannot pass

through the dielectric layer of a capacitor, rather an electron accumulates on the

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negative plate for each one that leaves the positive plate, resulting in an electron

depletion and consequent positive charge on one electrode that is equal and opposite

to the accumulated negative charge on the other.

Thus the charge on the electrodes is equal to the integral of the current as well as proportional

to the voltage as discussed above. As with any anti derivative, a constant of integration is

added to represent the initial voltage v (t0). This is the integral form of the capacitor equation,

Taking the derivative of this, and multiplying by C, yields the derivative form,

The dual of the capacitor is the inductor, which stores energy in a magnetic field rather than

an electric field. Its current-voltage relation is obtained by exchanging current and voltage in

the capacitor equations and replacing Cwith the inductance L.

Capacitors, together with resistors and inductors, belong to the group of passive

components in the range of components for electronic equipment. Although in absolute

figures the most often produced capacitors are integrated capacitors, f. e. in DRAMs or

in flash memorys structures these article is concentrated on capacitors as discrete

components.

Capacitors today are industrial products produced in very large quantities for use in electronic

and in electrical equipment. Globally, the market for fixed capacitors was estimated with

approximately US$18 billion in 2008 for 1,400 billion (1.4 x 1012) pieces. This market in

point of quantity is dominated by ceramic capacitors with estimated of approximately 1,000

billion (1 x 1012) produced pieces per year

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Detailed estimated figures in value for the main capacitor families are:

Ceramic capacitors with US$8.3 billion (46 %);

Aluminum electrolytic capacitors with US$ 3.9 billion (22 %);

Film capacitors and Paper capacitors with US$ 2.6 billion, (15 %);

Tantalum electrolytic capacitors with US$ 2.2 billion (12 %);

Super capacitors (Double-layer capacitors) with US$ 0.3 billion (2 %); and

others like silver mica and vacuum capacitors with US$ 0.7 billion (3 %).

A capacitor consists of two conductors separated by a non-conductive region. The non-

conductive region is called the dielectric. In simpler terms, the dielectric is just an electrical

insulator. Examples of dielectric media are glass, air, paper, vacuum, and even

a semiconductor depletion region chemically identical to the conductors. A capacitor is

assumed to be self-contained and isolated, with no net electric charge and no influence from

any external electric field.

The conductors thus hold equal and opposite charges on their facing surfaces, and the

dielectric develops an electric field. In SI units, a capacitance of one farad means that

one coulomb of charge on each conductor causes a voltage of one volt across the device.

The capacitor is a reasonably general model for electric fields within electric circuits. An

ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of

charge Q on each conductor to the voltage Vbetween them

Sometimes charge build-up affects the capacitor mechanically, causing its capacitance

to vary. In this case, capacitance is defined in terms of incremental changes:

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4.3.1 CAPACITOR COLOUR CODING

Capacitors may be marked with 3 or more colored bands or dots. The colors encode the first

and second most significant digits of the value, and the third color the decimal multiplier in

pico farads. Additional bands have meanings which may vary from one type to another. Low-

tolerance capacitors may begin with the first 3 (rather than 2) digits of the value. It is usually,

but not always, possible to work out what scheme is used by the particular colors used.

Cylindrical capacitors marked with bands may look like resistors.

Color Significantdigits

Multiplier Capacitancetolerance

Characteristic

DC

working

voltage

Operatingtemperature

EIA/vibration

Black 0 1 20% 55 C to +70

C10 to 55 Hz

Brown 1 10 1% B 100

Red 2 100 2% C 55 C to +85

C

Orange 3 1000 D 300

Yellow 4 10000 E 55 C to

+125 C10 to 2000 Hz

Green 5 0.5% F 500

Blue 6 55 C to

+150 C

Violet 7

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Grey 8

White 9 EIA

Gold 5%* 1000

Silver 10%

4.4 IC 7809

7809 is a voltage regulator integrated circuit(IC) which is widely used in electronic circuits.

Voltage regulator circuit can be manually built using parts available in the market but it will

take a lot of time to assemble those parts on a PCB. Secondly, the cost of those parts is

almost equal to the price of 7809 itself so professionals usually prefer to use 7809 IC

instead of making a voltage regulator circuit from scratch. Before you start using 7809, you

will need to know about the pin structure of IC 7809. Apparently, it looks like a transistor.

It has three pins. For a better understanding, I have given an image of 7809 bellow. Please

take a look.

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It is wise to use two .1uF capacitors on both input and output sides to filter any ripple or

distortion in voltage but it is not necessary. In the image, you can see that 12V are being

supplied on the input side of 7809 but the out put side of 7809 is outputting Regulated 9V.

As long as the input voltage remains above 9V, output voltage of 7809 will remain smooth

and regulated.

Please note that input voltage of 7809 can be up to 23V but under my experience, it is wise

to avoid input over 15V. 7809 is claimed to output 9V and almost 1.5A Current but again, I

have experienced that we should not put a load over 9V and 1A on it. Since we are using it

in power supply, the transfer of power will result in heat output. We will need to use a heat

sink with 7809 otherwise this heat can damage it. It is advised to use a 1A fuse on the

output side of 7809 and a 1.5A fuse on the input side of 7809 to avoid damage in case of

short circuit.

4.5 RESISTORS

A resistor is a passive two-terminal electrical component that implements electrical

resistance as a circuit element.

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The current through a resistor is in direct proportion to the voltage across the resistor's

terminals. This relationship is represented by Ohm's law:

where Iis the current through the conductor in units of amperes, Vis the potential difference

measured across the conductor in units of volts, and R is the resistance of the conductor in

units of ohms.

The ratio of the voltage applied across a resistor's terminals to the intensity of current in the

circuit is called its resistance, and this can be assumed to be a constant (independent of the

voltage) for ordinary resistors working within their ratings.

Resistors are common elements of electrical networks and electronic circuits and are

ubiquitous in electronic equipment. Practical resistors can be made of various compounds and

films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-

chrome). Resistors are also implemented within integrated circuits, particularly analog

devices, and can also be integrated into hybrid and printed circuits.

The electrical functionality of a resistor is specified by its resistance: common commercial

resistors are manufactured over a range of more than nine orders of magnitude. When

specifying that resistance in an electronic design, the required precision of the resistance may

require attention to the manufacturing tolerance of the chosen resistor, according to its

specific application. The temperature coefficient of the resistance may also be of concern in

some precision applications. Practical resistors are also specified as having a

maximum power rating which must exceed the anticipated power dissipation of that resistor

in a particular circuit: this is mainly of concern in power electronics applications.

Resistors with higher power ratings are physically larger and may require heat sinks. In a

high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage

of the resistor.

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Practical resistors have a series inductance and a small parallel capacitance; these

specifications can be important in high-frequency applications. In a low-noise

amplifier or pre-amp, the noise characteristics of a resistor may be an issue. The

unwanted inductance, excess noise, and temperature coefficient are mainly dependent on

the technology used in manufacturing the resistor. They are not normally specified

individually for a particular family of resistors manufactured using a particular

technology.

A family of discrete resistors is also characterized according to its form factor, that is, the

size of the device and the position of its leads (or terminals) which is relevant in the

practical manufacturing of circuits using them.

Electronic symbols and notation:

The symbol used for a resistor in a circuit diagram varies from standard to standard and

country to country. Two typical symbols are as follows;

American-style symbols. (a) rheostat (b) potentiometer

IEC-style resistor symbol

The notation to state a resistor's value in a circuit diagram varies, too. The European notation

avoids using a decimal separator, and replaces the decimal separator with the SI prefix

symbol for the particular value. For example, 8k2 in a circuit diagram indicates a resistor

value of 8.2 k. Additional zeros imply tighter tolerance, for example 15M0. When the value

can be expressed without the need for an SI prefix, an 'R' is used instead of the decimal

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separator. For example, 1R2 indicates 1.2 , and 18R indicates 18 . The use of a SI prefix

symbol or the letter 'R' circumvents the problem that decimal separators tend to 'disappear'

when photocopying a printed circuit diagram.

THEORY OF OPERATION

The hydraulic analogy compares electric current flowing through circuits to water flowing

through pipes. When a pipe (left) is filled with hair (right), it takes a larger pressure to

achieve the same flow of water. Pushing electric current through a large resistance is like

pushing water through a pipe clogged with hair: It requires a larger push (voltage drop) to

drive the same flow (electric current).

Ohm's law

The behavior of an ideal resistor is dictated by the relationship specified by Ohm's law:

Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where

the constant of proportionality is the resistance (R).

Equivalently, Ohm's law can be stated:

This formulation states that the current (I) is proportional to the voltage (V) and inversely

proportional to the resistance (R). This is directly used in practical computations. For

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example, if a 300 ohm resistor is attached across the terminals of a 12 volt battery, then a

current of 12 / 300 = 0.04 amperes (or 40 milliamperes) flows through that resistor.

Series and parallel resistorsIn a series configuration, the current through all of the resistors is the same, but the voltage

across each resistor will be in proportion to its resistance. The potential difference (voltage)

seen across the network is the sum of those voltages, thus the total resistance canbe found as

the sum of those resistances:

As a special case, the resistance of N resistors connected in series, each of the same resistance

R, is given by NR.

Resistors in a parallel configuration are each subject to the same potential difference

(voltage), however the currents through them add. The conductances of the resistors then add

to determine the conductance of the network. Thus the equivalent resistance (Req) of the

network can be computed:

The parallel equivalent resistance can be represented in equations by two vertical lines "||" (as

in geometry) as a simplified notation. Occasionally two slashes "//" are used instead of "||", in

case the keyboard or font lacks the vertical line symbol. For the case of two resistors in

parallel, this can be calculated using:

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As a special case, the resistance of N resistors connected in parallel, each of the same

resistance R, is given by R/N.A resistor network that is a combination of parallel and series

connections can be broken up into smaller parts that are either one or the other. For instance,

However, some complex networks of resistors cannot be resolved in this manner, requiring

more sophisticated circuit analysis. For instance, consider a cube, each edge of which has

been replaced by a resistor. What then is the resistance that would be measured between two

opposite vertices? In the case of 12 equivalent resistors, it can be shown that the corner-to-

corner resistance is 56 of the individual resistance. More generally, the Y- transform,

or matrix methods can be used to solve such a problem.

One practical application of these relationships is that a non-standard value of resistance cangenerally be synthesized by connecting a number of standard values in series or parallel. This

can also be used to obtain a resistance with a higher power rating than that of the individual

resistors used. In the special case of N identical resistors all connected in series or all

connected in parallel, the power rating of the individual resistors is thereby multiplied by N.

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Power dissipation

The power P dissipated by a resistor is calculated as:

The first form is a restatement of Joule's first law. Using Ohm's law, the two other forms can

be derived.

The total amount of heat energy released over a period of time can be determined from the

integral of the power over that period of time:

Resistors are rated according to their maximum power dissipation. Most discrete resistors insolid-state electronic systems absorb much less than a watt of electrical power and require no

attention to their power rating. Such resistors in their discrete form, including most of the

packages detailed below, are typically rated as 1/10, 1/8, or 1/4 watt.

Resistors required to dissipate substantial amounts of power, particularly used in power

supplies, power conversion circuits, and power amplifiers, are generally referred to as power

resistors; this designation is loosely applied to resistors with power ratings of 1 watt or

greater. Power resistors are physically larger and may not use the preferred values, color

codes, and external packages described below.

If the average power dissipated by a resistor is more than its power rating, damage to the

resistor may occur, permanently altering its resistance; this is distinct from the reversible

change in resistance due to its temperature coefficient when it warms. Excessive power

dissipation may raise the temperature of the resistor to a point where it can burn the circuit

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board or adjacent components, or even cause a fire. There are flameproof resistors that fail

(open circuit) before they overheat dangerously.

Since poor air circulation, high altitude, or high operating temperatures may occur, resistorsmay be specified with higher rated dissipation than will be experienced in service. Some

types and ratings of resistors may also have a maximum voltage rating; this may limit

available power dissipation for higher resistance values.

4.5.1 RESISTOR COLOUR CODING

The electronic color code is used to indicate the values or ratings of electronic components,

very commonly for resistors, but also for capacitors, inductors, and others. A separate code,

the 25-pair color code, is used to identify wires in some telecommunications cables.

The electronic color code was developed in the early 1920s by the Radio Manufacturers

Association (now part of Electronic Industries Alliance (EIA), and was published as EIA-RS-

279. The current international standard is IEC 60062.

Color bands were commonly used (especially on resistors) because they were easily printed

on tiny components, decreasing construction costs. However, there were drawbacks,

especially for color blind people. Overheating of a component, or dirt accumulation, may

make it impossible to distinguish brown from red from orange. Advances in printing

technology have made printed numbers practical for small components, which are often

found in modern electronics.

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A 2.26 kilo-ohm, 1% precision resistor with 5 color bands (E96 series), from top 2-2-6-1-1; the last

two brown bands indicate the multiplier (x10), and the 1% tolerance.

To distinguish left from right there is a gap between the C and D bands.

band A is first significant figure of component value (left side)

band B is the second significant figure (Some precision resistors have a third significant

figure, and thus five bands.)

band C is the decimal multiplier

band D if present, indicates tolerance of value in percent (no band means 20%)

For example, a resistor with bands of yellow, violet, red, and gold will have first digit 4

(yellow in table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold

signifies that the tolerance is 5%, so the real resistance could lie anywhere between 4,465

and 4,935 ohms.

Resistors manufactured for military use may also include a fifth band which indicates

component failure rate (reliability); refer to MIL-HDBK-199 for further details.

Tight tolerance resistors may have three bands for significant figures rather than two, or an

additional band indicating temperature coefficient, in units of ppm/K.

All coded components will have at least two value bands and a multiplier; other bands are

optional.

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The standard color code per EN 60062:2005 is as follows:

ColorSignificant

figuresMultiplier Tolerance

Temp.

Coefficient

(ppm/K)

Black 0 100

250 U

Brown 1 101 1% F 100 S

Red 2 102 2% G 50 R

Orange 3 103

15 P

Yellow 4 104

(5%) 25 Q

Green 5 105

0.5% D 20 Z

Blue 6 106

0.25% C 10 Z

Violet 7 107

0.1% B 5 M

Gray 8 108 0.05%

(10%)A 1 K

White 9 109

Gold 10-1 5% J

Silver 10-2 10% K

None 20% M

1. Any temperature coefficient not assigned its own letter shall be marked

"Z", and the coefficient found in other documentation.

2. Yellow and Gray are used in high-voltage resistors to avoid metal particles

in the lacquer.

Resistors use preferred numbers for their specific values, which are determined by

their tolerance. These values repeat for every decade of magnitude: 6.8, 68, 680, and so forth.

In the E24 series the values are related by the 24th root of 10, while E12 series are related by

the 12th root of 10, and E6 series by the 6th root of 10. The tolerance of device values is

arranged so that every value corresponds to a preferred number, within the required tolerance.

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Zero ohm resistors are made as lengths of wire wrapped in a resistor-shaped body which can

be substituted for another resistor value in automatic insertion equipment. They are marked

with a single black band.

The 'body-end-dot' or 'body-tip-spot' system was used for radial-lead (and other cylindrical)

composition resistors sometimes still found in very old equipment; the first band was given

by the body color, the second band by the color of the end of the resistor, and the multiplier

by a dot or band around the middle of the resistor. The other end of the resistor was colored

gold or silver to give the tolerance, otherwise it was 20%.

Extra bands on ceramic capacitors will identify the voltage rating class and temperature

coefficient characteristics. A broad black band was applied to some tubular paper capacitors

to indicate the end that had the outer electrode; this allowed this end to be connected to

chassis ground to provide some shielding against hum and noise pickup.

Polyester film and "gum drop" tantalum electrolytic capacitors are also color coded to give

the value, working voltage and tolerance.

4.6 555 IC

Integrated Circuit:

An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a

microchip) is an electronic circuit on one small plate ("chip") of semiconductor material,normally silicon. Such a circuit can be made very compact, having up to several billion

transistors and other electronic components.

Timer:

A timer is a specialized type of clock for measuring time intervals. Different types of timers:

Mechanical timers, Electro mechanical timers, Electronic timers, and Computer timers.

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The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation,

and oscillator applications. The 555 can be used to provide time delays, as an oscillator, and

as a flip-flop element. Introduced in 1972 by Signetics, the 555 is still in widespread use, due

to its ease of use, low price, and good stability. It is now made by many companies in the

original bipolar and also in low-power CMOS types.

INTERNAL BLOCK DIAGRAM OF IC NE 555 TIMER:

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DESCRIPTION

The NE555 contains 24 bipolar transistors, two diodes and 15 resistors that form six

functional blocks. Between the supply voltage VCC (+) and the ground GND (-) is a voltage

divider consisting of three identical resistors which, when connected not from the outside, the

two reference voltages / 3 VCC and / 3 VCC supplies. The latter is at the terminal pin

Control Voltage available. The block diagram and schematic that area is highlighted in green.

Two comparators are each connected to one of the reference voltages, while the other two

inputs of which are fed directly to the terminals of trigger or threshold. The block diagram in

yellow and orange. A flip-flop, deposited in the color purple, stores the state of the timer and

is controlled by the two comparators. Via the reset terminal overrides the other two inputs,

the flip-flop (and therefore the entire timer device) be reset at any time. At the output of flip-

flop followed by an output stage with totem-pole output that can be loaded at the port output

with up to 200 mA. Shown in the color pink.

Parallel to the output stage of a transistor is connected, the collector is located on the

discharge port. The transistor in the circuit diagram is a light blue background, always

energized when the output is low level.

PIN DIAGRAM OF 555 IC

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Pin Name Purpose

1 GND All the voltages are meas-ured with respect to thisterminal.

2 TRIG This pin is an inverting

input to a comparator thatis responsible for transitionofflip-flop from set toreset.

3 OUT Output of the timer isavailable at this pin.

4 RESET To disable or reset thetimer a negative pulse isapplied to this pin due towhich it is referred to asreset terminal.

5 CTRL The function of thisterminal is to control thethreshold and triggerlevels.

6 THR It is the non-inverting inputterminal of comparator 1,

which compares the voltageapplied to the terminal witha reference voltage of 2/ 3

VCC.7 DIS This pin is connected

internally to the collector of

transistor and mostly acapacitor is connectedbetween this terminal andground. It is calleddischarge terminal becausewhen transistor saturates,capacitor dischargesthrough the transistor.

8 VCC A supply voltage of + 5 V to+ 18 V is applied to thisterminal with respect to

ground (pin 1).

Note-PIN 5 is also called the CONTROL VOLTAGE pin By applying a voltage to the

CONTROL VOLTAGE input you can alter the timing characteristics of the device. In most

applications, the CONTROL VOLTAGE input is not used. It is usual to connect a 10 nF

capacitor between pin 5 and 0 V to prevent interference. The CONTROL VOLTAGE input

can be used to build an astable with a frequency modulated output.

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Modes:

The 555 has three operating modes:

Monostable mode: in this mode, the 555 functions as a "one-shot" pulse generator.

Applications include timers, missing pulse detection, bounce free switches, touch switches,

frequency divider, capacitance measurement, pulse-width modulation (PWM) and so on.

Astable: Free running mode: the 555 can operate as an oscillator. Uses include LED and

lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position

modulation and so on. The 555 can be used as a simple ADC, converting an analog value to a

pulse length. E.g. selecting a thermistor as timing resistor allows the use of the 555 in a

temperature sensor: the period of the output pulse is determined by the temperature. The use

of a microprocessor based circuit can then convert the pulse period to temperature, linearize it

and even provide calibration means.

Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not

connected and no capacitor is used. Uses include bounce-free latched switches.

4.7 RELAY

A relay is an electrically operated switch. Many relays use an electromagnet to operate a

switching mechanism mechanically, but other operating principles are also used. Relays are

used where it is necessary to control a circuit by a low-power signal or where several circuits

must be controlled by one signal. The first relays were used in long distance telegraph

circuits, repeating the signal coming in from one circuit and re-transmitting it to another.

Relays were used extensively in telephone exchanges and early computers to perform logical

operations.

A type of relay that can handle the high power required to directly control an electric motor

or other loads is called a contractor. Solid-state relays control power circuits with no moving

parts, instead using a semiconductor device to perform switching. Relays with calibrated

operating characteristics and sometimes multiple operating coils are used to protect electrical

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circuits from overload or faults; in modern electric power systems these functions are

performed by digital instruments still called "protective relays".

Basic design and operation:

Small "cradle" relay often used in electronics.The "cradle" term refers to the shape of the relay's

armature.

A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an

iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature,

and one ormore sets of contacts (there are two in the relay pictured). The armature is hinged

to the yoke and mechanically linked to one or more sets of moving contacts. It is held in

place by a spring so that when the relay is de-energized there is an air gap in the magnetic

circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and

the other set is open. Other relays may have more or fewer sets of contacts depending on their

function. The relay in the picture also has a wire connecting the armature to the yoke. This

ensures continuity of the circuit between the moving contacts on the armature, and the circuit

track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.

When an electric current is passed through the coil it generates a magnetic field that activates

the armature, and the consequent movement of the movable contact(s) either makes or breaks

a connection with a fixed contact. If the set of contacts was closed when the relay was de-

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energized, then the movement opens the contacts and breaks the connection, and vice versa if

the contacts were open.

When the current to the coil is switched off, the armature is returned by a force,

approximately half as strong as the magnetic force, to its relaxed position. Usually this force

is provided by a spring, but gravity is also used commonly in industrial motor starters. Most

relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in

a high voltage or current application it reduces arcing. When the coil is energized with direct

current, a diode is often placed across the coil to dissipate the energy from the collapsing

magnetic field at deactivation, which would otherwise generate a voltage spike dangerous

to semiconductor circuit components.

Some automotive relays include a diode inside the relay case. Alternatively, a contact

protection network consisting of a capacitor and resistor in series (snubber circuit) may

absorb the surge. If the coil is designed to be energized with alternating current (AC), a small

copper "shading ring" can be crimped to the end of the solenoid, creating a small out-of-

phase current which increases the minimum pull on the armature during the AC cycle.

A solid-state relay uses a thyristor or other solid-state switching device, activated by the

control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-

emitting diode (LED) coupled with a photo transistor) can be used to isolate control and

controlled circuits.

4.8 TRANSISTORS

A transistor is a semiconductor device used to amplify and switch electronic signals and

electrical power. It is composed of semiconductor material with at least three terminals for

connection to an external circuit. A voltage or current applied to one pair of the transistor's

terminals changes the current flowing through another pair of terminals.

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Because the controlled (output) power can be higher than the controlling (input) power, a

transistor can amplify a signal. Today, some transistors are packaged individually, but many

more are found embedded in integrated circuits. The transistor is the fundamental building

block of modern electronic devices, and is ubiquitous in modern electronic systems.

Following its development in the early 1950s the transistor revolutionized the field of

electronics, and paved the way for smaller and cheaper radios, calculators, and computers,

among other things.

Transistor as a switch

Transistors are commonly used as electronic switches, both for high-power applications such

as switched-mode power supplies and for low-power applications such as logic gates.

In a grounded-emitter transistor circuit, such as the light-switch circuit shown, as the base

voltage rises, the emitter and collector currents rise exponentially. The collector voltage drops

because of the collector load resistance (in this example, the resistance of the light bulb). If

the collector voltage were zero, the collector current would be limited only by the light bulb

resistance and the supply voltage.

The transistor is then said to be saturated- it will have a very small voltage from collector to

emitter. Providing sufficient base drive current is a key problem in the use of bipolar

transistors as switches.

The transistor provides current gain, allowing a relatively large current in the collector to be

switched by a much smaller current into the base terminal. The ratio of these currents varies

depending on the type of transistor, and even for a particular type, varies depending on the

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collector current. In the example light-switch circuit shown, the resistor is chosen to provide

enough base current to ensure the transistor will be saturated.

In any switching circuit, values of input voltage would be chosen such that the output is

either completely off or completely on. The transistor is acting as a switch, and this type of

operation is common in digital circuits where only "on" and "off" values are relevant.

Transistor as an amplifier

The common-emitter amplifier is designed so that a small change in voltage (Vin) changes the

small current through the base of the transistor; the transistor's current amplification

combined with the properties of the circuit mean that small swings in Vinproduce large

changes in Vout. Various configurations of single transistor amplifier are possible, with some

providing current gain, some voltage gain, and some both.

From mobile phones to televisions, vast numbers of