94954580 Automatic Control of Street Light

Feel free to contact at : [email protected]

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AUTOMATIC CONTROL OF STREET LIGHT

MAJOR PROJECT REPORT

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE

OF

BACHELOR OF TECHNOLOGY IN

ELECTRICAL ENGINEERING

Submitted by:

Malik Sameeullah Muneeb Ahmed Rizwanullah Ansari

(08EES31) (08EES50) (08EES62)

Under the supervision of

DR. TARIKUL ISLAM

ASSOCIATE PROFESSOR

DEPARTMENT OF ELECTRICAL ENGINEERING FACULTY OF ENGINEERING &TECHNOLOGY

JAMIA MILLIA ISLAMIA NEW DELHI-110025 INDIA

2012


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AUTOMATIC CONTROL OF STREET LIGHT

MAJOR PROJECT REPORT

SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE

OF

BACHELOR OF TECHNOLOGY IN

ELECTRICAL ENGINEERING

Submitted by:

MALIK SAMEEULLAH (08-EES 31)

MUNEEB AHMED (08-EES 50)

RIZWANULLAH ANSARI (08-EES 62)

Under the supervision of

DR. TARIKUL ISLAM

ASSOCIATE PROFESSOR

DEPARTMENT OF ELECTRICAL ENGINEERING FACULTY OF ENGINEERING &TECHNOLOGY

JAMIA MILLIA ISLAMIA NEW DELHI-110025 INDIA

2012


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DEPARTMENT OF ELECTRICAL ENGINEERING FACULTY OF ENGINEERING AND TECHNOLOGY

JAMIA MILLIA ISLAMIA NEW DELHI-110025

CERTIFICATE

This is to certify that the major Project titled “AUTOMATIC CONTROL OF STREET

LIGHT” submitted in partial fulfillment of the requirements for the award of the degree

of Bachelor of Technology in Electrical Engineering by Malik Sameeullah (08EES-31),

Muneeb Ahmed (08 EES-50) & Rizwanullah Ansari (08EES-62) is a bonafide record

of the candidate‘s own work carried out by them under my supervision and guidance.

This work has not been submitted earlier in any university or institute for the award of any

degree to the best of my knowledge.

[Project Supervisor]

DR. TARIKUL ISLAM

Associate Professor

Dept. of Electrical Engineering

Jamia Millia Islamia

New Delhi-110025

Prof. ZAHEERUDIN (HOD)

Department of Electrical Engineering

Jamia Millia Islamia


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ACKNOWLEDGEMENT

We first thank our parents who gave us the moral support right from the moment

we thought about this project and who have provided us with opportunity to serve

the society as engineers

We express our sincere thanks to Prof. Zaheeruddin, Head of the Department of

Electrical Engineering for his work & cooperation to facilitate smooth progress of

the project.

We express our sincere thanks to our project guide Dr. Tarikul Islam for his

constant support, motivation and encouragement without which it would have been

very difficult for us to complete the project. He gave us the freedom to think and

made open all the resources he had in his personal capacity.

We would also like to thank Lab Assistants, Mr. Lokesh Kumar who is a Phd

scholars for his constant support and motivation and our friends for their constant

support, sacrifice and their encouragement.

Above all we would like to thank the almighty God for everything he has bestowed

on us.

MALIK SAMEEULLAH

MUNEEB AHMED

RIZWANULLAH ANSARI


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TABLE OF CONTENTS PAGE No.

ACKNOWLEDGEMENT iii

Abstract

CHAPTER 1: INTRODUCTION 1-2

CHAPTER 2:TECHNICAL REVIEW 3-9

2.1 Thyristor and its conduction

2.2 Line commutated converters

2.3 Necessity of getting synchronizing pulses

2.4 Popular methods of generating firing pulses

2.5 Basic building blocks

2.6 Block diagram representation of cosine control

CHAPTER 3: TECHNICAL LITERATURE REVIEW 10-40

3.1 Thyristor

3.2 Typical Thyristor characteristic

3.3 Firing Technique of Thyristor

3.4 Basic building Blocks

3.5 Unijunction Transistor

3.6 Triac

3.7 Op Amp

3.8 Firing Pulse technique

3.9 Transistor as a Switch

3.10 The 555 Timer

3.11 light dependent resistor


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3.12 Optocoupler

3.13 DC supply system

3.14 Street light

CHAPTER 4: PROPOSED PROJECT WORK 41-52

4.1 Synchronizing part

4.2 Cosine wave generator

4.3 Comparator for producing variable width pulse

4.4 Automatic variable voltage generator

4.5 Automatic on off circuit

4.6 Triac firing circuit

CHAPTER 5: CONCLUSION 53

5.1 Summary of the work reported in the project

5.2 Scope of future work

APPENDIX

REFERENCES


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ABSTRACT The theme of the project is to design the automatic control of street light with change of the

intensity of sunlight i.e.as the intensity of sunlight decreases, intensity of street light increases. LDR

is used to detect light intensity. Once there is enough darkness, circuit will turn on. Triac controlled

circuit is used to control the intensity of light. In this project there is the necessity of getting

synchronized firing pulses for the gate of the thyristor. Out of many variety of firing circuits

available, cosine controls scheme is used. In this interesting scheme, the supply voltage is first

integrated to obtain a cosine wave. The cosine wave so obtained is compared with a reference D.C

voltage. Therefore square pulses will be generated at the output terminal of the comparator. The

signal at output terminal is synchronized with the pulse and is delayed from the supply zero

crossing by an angle α. Instrumentation Op amp is used to provide a reference voltage to a firing

circuit. And this reference voltage is totally dependent on LDR resistance whose value change with

intensity of light.

This circuit is analysed and tested in various conditions and it provides absolute results which

shows the reliability of this circuit. Usually street light remain ON in morning time due to manual

operation, which cause loss of energy and therefore this project is very beneficial for saving power

and energy by automatic control. This circuit also provides the idea of developing the driver circuit

of LED lamp which is widely used nowadays.


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CHAPTER 1

INTRODUCTION

The main consideration in the present field technologies are automation, power consumption and

cost effectiveness. Automation is intended to reduce manpower with the help of intelligent systems.

Power saving is the main consideration forever as the source of the power (thermal, hydro etc.,) are

getting diminished due to various reasons. The main aim of the project is automatic street power

saving system with LDR; this is to save the power. We want to save power automatically instead of

doing manual. So it‘s easy to make cost effectiveness. This saved power can be used in some other

cases. So in villages, towns etc we can design intelligent systems for the usage of street lights.

Block diagram to implement circuit is shown in below figure.

MERITS AND DEMERITS OF OUR PROJECT:

In recent years the energy crisis has become one problem which the whole world must confront.

Home power consumption makes up the largest part of energy consumption in the world. In

particular, the power consumption of lamps in a typical home is a factor which can‘t be ignored.

The typical user needs different light intensities in different places. Sometimes the light intensity

from outside is sufficient, and thus we don‘t need to turn on any light. But sometimes the user


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leaves the room but forgets to turn off the light. These factors cause energy wastage. Therefore

some power management of light control in a home is necessary in order to save energy. Lights are

usually controlled by on/off switches. Of course, the user can switch a light on or off remotely by

connecting a specific device to a PC, but there has to be at least a PC, consuming a rather large

amount of power 24 hours a day, for the control mechanism. Moreover, this inconvenient practice

comes at a high cost for the user. In some designs one must install specific hardware and software

to control the lights, resulting in unacceptable costs. Furthermore this type of system cannot detect

either the temperature of the human body or light intensity of room.


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CHAPTER 2 TECHNICAL REVIEW

Thyristors or Silicon Controlled Rectifiers (SCRs) are widely used as a switching device in the

medium and large power levels starting from few kilowatts to several mega watts at voltage levels

of few hundred to several kilo volt levels. Bipolar Junction Transistors (BJTs) and Metal Oxide

Semiconductor Field Effect Transistors (MOSFETs) although have very fast switching

characteristics compared to SCRs, their uses are limited to medium power levels at few hundred

volts.

2.1 THYRISTOR & ITS CONDUCTION

A thyristor or SCR is a four layer device having three junctions J1, J2 and J3. Essentially three

terminals named anode, cathode and gate. Thyristor will be in reverse blocking mode if VAK < 0,

irrespective of the fact that a gate pulse is present or not. On the other hand the thyristor is said to

be in the forward blocking mode, when VAK > 0 in absence of any gate pulse, some current will

flow through the thyristor. In case of the thyristor is turning on either by exceeding the forward

break-over voltage or by applying a gate pulse between gate and cathode, called forward conduction

mode.

Fig 2.1 Symbol of diode and thyristor


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2.2 LINE COMMUTATED CONVERTERS

Conversion of line frequency (50 Hz) a.c. to d.c. is carried out either by using a single phase bridge

converter using four thyristors or 3-phase converter using six thyristors. A single phase fully

controlled bridge with four thyristor. With reference to the single phase converter circuit shown in

Fig.2.2 , we note that when B or positive, two diagonally opposite thyristors T and T are

forward biased and other two thyristors T and T are reversed biased. Therefore during intervals

i.e. to gate pulses are simultaneously applies to T and T , both start conducting and load

voltage = and also T3 and T4 are reversed biased and cannot conduct at that period of time

and vice versa.

Fig 2.2 Fully controlled converter

2.3 NECESSITY OF GETTING SYNCHRONIZING PULSES

For T and T , α is to be measured from the instant when is zero and going towards positive.

Similarly T and T , α is to be measured from the instant is zero and going towards positive.

Thus we see that for successful operation of the fully controlled bridge, the gate pulses to be

properly synchronized with the a.c. power supply. It is noted that each thyristor conducts for

only.


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Fig. 2.3 Typical waveform of single phase inverter

2.4 POPULAR METHODS OF GENERATING FIRING PULSES

1) Using ramp signal: In this scheme a ramp signal is generated in synchronism with the a.c.

supply. The first comparator translates the input sinusoidal voltage into a square wave voltage.

When the square wave voltage is high, the transistor (P-N-P type) collector-base junction is

forward biased; the transistor is non conducting stage (off) and the capacitor charges

exponentially giving ramp rise of the voltage at the output. However, as soon as the square

voltage is negative, transistor becomes on due to collector-base junction is reverse biased and

the capacitor discharges sharply giving a saw tooth like waveform as shown in Fig. 2.4.

Fig. 2.4 Basic idea of ramp scheme


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This triangular voltage can now be compared by the second comparator with a variable

reference d.c. voltage ref to get the firing pulse signal at . The value of α can be varied in

the range α by changing the value of the reference voltage (Vref).

2). Using cosine control: In this interesting scheme, the supply voltage Vs is first integrated to

obtain a cosine wave as shown in Fig. 2.5. The cosine wave so obtained is compared with a

reference d.c. voltage (Vref). Therefore square pulses will be generated at the output terminal

of the comparator. The signal at is synchronized with the pulse and is delayed from the

supply zero crossing by an angle α. Obviously, the value of α can be varied a range of α

.

Fig 2.5 basic idea of cosine scheme

2.5 BASIC BUILDING BLOCKS

Basic blocks which will be necessary to implement any firing control scheme in a converter circuit

are shown in Fig.2.6. The figure demonstrates with the help of a single line diagram, the major

blocks necessary to generate firing pulses for any scheme. The converter is organized from a.c.

power. Since the firing pulses must be synchronized with the a.c. supply, a.c. power also goes to the

isolation and synchronizing blocks. Isolation is essential as because the control circuit uses very

low power devices such as various chips, logic gates etc.


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Fig 2.6 Basic block of firing control circuit

The logic circuit block uses few logic gates to implement a particular firing scheme. The strength of

the pulse obtained from logic gates may not be sufficient to drive the gate of a thyristor, so

amplification of the pulse along with isolation is used at final stage.

2.6 BLOCK DIAGRAM REPRESENTATION OF THE COSINE

The emphasis of this paper is the implementation of cosine control scheme. We shall first outline

the scheme in terms of block diagram and then explain each block in detail. Let be the supply

voltage feeding the converter for which the control pulses are to be generated. With the help of a

step down centre tapped transformer, is transformed into two power level voltage and .

T1 & T2 are to be fired when Va0 is positive and T3 & T4 are to be fired when is positive. For

T & T the firing angle α is to be measured from the instant when a is zero and increasing in

the positive direction. The range of variation of α is to . Similarly for T & T the firing angle

α is to be measured from the instant when b is zero and increasing in the positive direction. Basic

idea for generating necessary pulses for T1 & T2 and T3 & T4 can be understood by referring

figures 2.7 and 2.8.

With reference to Fig. 8 the signal Va0 is integrated with the help of Integrator -1 and a cosine

wave will be obtained. This cosine wave is compared with a variable d.c. voltage Vr using a

comparator-1. Noting that Vr is connected to the +ve terminal of the comparator-1, the output of the

comp-1 will be square wave and it goes to high state from the instant when Vr becomes greater than

the cosine voltage value. However the width of the pulse will vary as Vr is varied. Our first aim will


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be to make the width of the pulse to be . This is achieved in the following way. The output of

the comp- is fed to a block mono- . Output of the mono will be a pulse of small width at positive

going edge of the input square wave. The output of mono- will thus give small pulses separated by

. Noting that Vr is connected to the +ve terminal of the comparator-1, the output of the comp-1

will be square wave and it goes to high state from the instant when Vr becomes greater than the

cosine voltage value. However the width of the pulse will vary as r is varied. Our first aim will be

to make the width of the pulse to be . This is achieved in the following way. The output of the

comp-1 is fed to a block mono-1. Output of the mono will be a pulse of small width at positive

going edge of the input square wave. The output of mono- will thus give small pulses separated by

.

Fig. 2.7 Basic Block of control scheme

The voltage Vb0 is similarly processed, i.e., it is integrated then compared with the same variable

d.c. with the help of comparator-2, output of OMP- will be a square wave and will be shifted by

from the output square wave of OMP-1. This is because of the fact that Vb0 lags Va0 by .

The output of the comp-2 is now fed to a block mono-2. Output of mono-2 will be a pulse of small

width at positive going edge of the input square wave. The output of mono-2 will thus give small

pulses separated by .


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Fig. 2.8: Wave form at different point of ckt. of fig 2.7

This is important to know that the fixed width pulse waveforms at the output of mono- and mono-

are shifted by as shown in Fig. 2.8. The outputs of mono1 and mono-2 can be used in

conjunction with to two S-R flip flops so as to generate two square waves each having a fixed width

of and mutually separated by . By some modification this technique can be used for

voltage control.


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CHAPTER 3

LITERATURE REVIEW

3.1 THYRISTOR:

Thyristors or silicon controlled rectifiers (SCR) are finding many uses in electronics, and in

particular for power control. Thyristors or silicon controlled rectifiers( SCRs) have even been called

the workhorse of high power electronics. The thyristor is a four-layered, three terminal

semiconducting devices, with each layer consisting of alternately N-type or P-type material, for

example P-N-P-N. The main terminals, labelled anode and cathode, are across the full four layers,

and the control terminal, called the gate, is attached to p-type material near to the cathode. (A

variant called an SCS—Silicon Controlled Switch—brings all four layers out to terminals.) The

operation of a thyristor can be understood in terms of a pair of tightly coupled bipolar junction

transistors, arranged to cause the self-latching action.

Fig. 3.1 Structure on the physical and electronic level, and the thyristor symbol.

3.2 TYPICAL THYRISTOR CHARACTERISTICS:

Figure 3.2 shows a typical characteristic curve for a thyristor. It can be seen that in the reverse

biased region it behaves in a similar way to a diode. All current, apart from a small leakage current

is blocked (reverse blocking region) until the reverse breakdown region is reached, at which point

the insulation due to the depletion layers at the junctions breaks down.

http://en.wikipedia.org/wiki/N-type_semiconductor

http://en.wikipedia.org/wiki/P-type_semiconductor

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

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


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In the forward biased mode, unlike a normal diode, no current apart from a small leakage current

flows. This is called the forward blocking mode. If a gating pulse is applied however, the thyristor

"fires" and the forward resistance of the device falls to a very low value, allowing very large

(several amperes) currents to flow in the forward conducting mode. Thyristors can also be made to

fire by applying a very large forward voltage between anode and cathode, but this is not desirable as

the device is not then being used to control conduction.

Fig. 3.2 Characteristics of SCR.

3.3 FIRING TECHNIQUE OF THYRISTOR:

An SCR can be switched from off state to on state in several ways and these are: forward voltage

triggering, temperature triggering, light triggering and gate triggering. Gate triggering is, however,

the most common method of turning on the SCRs, because this method lends itself accurately for

turning on the SCR at the desired instant of time. In addition gate triggering is an efficient and

reliable method.

3.4 BASIC BUILDING BLOCKS:

Basic blocks which will be necessary to implement any firing control scheme in a converter circuit

are shown in Fig. 3.3. The figure demonstrates with the help of a single line diagram, the major


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blocks necessary to generate firing pulses for any scheme. The converter is organized from a.c.

power. Since the firing pulses must be synchronized with the a.c. supply, a.c. power also goes to the

isolation and synchronizing blocks. Isolation is essential as because the control circuit uses very

low power devices such as various chips, logic gates etc. The logic circuit block uses few logic

gates to implement a particular firing scheme. The strength of the pulse obtained from logic gates

may not be sufficient to drive the gate of a thyristor, so amplification of the pulse along with

isolation is used at final stage as shown Fig. 3.3.

Fig. 3.3 Basic block of firing control circuit.

3.5 UNIJUNCTION TRANSISTOR:

Although a unijunction transistor is not a thyristor, this device can trigger larger thyristors with a

pulse at base B1. A unijunction transistor is composed of bar of N-type silicon having a P-type

connection in the middle. See Figure 3.4(a). The connections at the ends of the bar are known as

bases B1 and B2; the P-type mid-point is the emitter. With the emitter disconnected, the total

resistance RBBO, a datasheet item, is the sum of RB1 and RB2 as shown in Figure 3.4(b). RBBO ranges

from 4- kΩ for different device types. The intrinsic standoff ratio η is the ratio of RB1 to RBBO. It

varies from 0.4 to 0.8 for different devices. The schematic symbol is Figure 3.4(c).

http://www.allaboutcircuits.com/vol_3/chpt_7/8.html#03504.png


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Fig 3.4 Symbol and formula of UJT

The Unijunction emitter current vs voltage characteristic curve (Figure 3.5 (a)) shows that as

VE increases, current IE increases up IP at the peak point. Beyond the peak point, current increases

as voltage decreases in the negative resistance region. The voltage reaches a minimum at the valley

point. The resistance of RB1, the saturation resistance is lowest at the valley point.

IP and IV, are datasheet parameters; for a 2n2647, IP and IV are 2µA and 4mA,

respectively. [AMS] VP is the voltage drop across RB1 plus a 0.7V diode drop; see Figure 3.5 (b).

VV is estimated to be approximately 10% of VBB.

Fig 3.5 V-I characteristic of UJT


http://www.allaboutcircuits.com/vol_3/chpt_7/8.html#AMS.bibitem



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The relaxation oscillator in Figure 3.6 below is an application of the unijunction oscillator. RE

charges CE until the peak point. The unijunction emitter terminal has no effect on the capacitor until

this point is reached. Once the capacitor voltage, VE, reaches the peak voltage point VP, the lowered

emitter-base1 E-B1 resistance quickly discharges the capacitor. Once the capacitor discharges

below the valley point VV, the E-RB1 resistance reverts back to high resistance, and the capacitor is

free to charge again.

Fig.3.6 Unijunction transistor relaxation oscillator and waveforms.

3.6 TRIAC:

Triac is an electronic component that can conduct current in either direction when it is triggered

(turned on), and is formally called a bidirectional triode thyristor or bilateral triode thyristor.

Triacs belong to the thyristor family and are closely related to Silicon-controlled rectifiers (SCR).

However, unlike SCRs, which are unidirectional devices (i.e. can conduct current only in one

direction), TRIACs are bidirectional and so current can flow through them in either direction.

Another difference from SCRs is that TRIACs can be triggered by either a positive or a negative

current applied to its gate electrode, whereas SCRs can be triggered only by currents going into the

gate. In order to create a triggering current, a positive or negative voltage has to be applied to the

gate with respect to the A1 terminal (otherwise known as MT1).

Once triggered, the device continues to conduct until the current drops below a certain threshold,

called the holding current.


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

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

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

http://en.wikipedia.org/wiki/Silicon-controlled_rectifier

http://en.wikipedia.org/wiki/Silicon_controlled_rectifier#Modes_of_operation


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The bidirectionality makes TRIACs very convenient switches for AC circuits, also allowing them to

control very large power flows with milliampere-scale gate currents. In addition, applying a trigger

pulse at a controlled phase angle in an AC cycle allows one to control the percentage of current that

flows through the TRIAC to the load (phase control), which is commonly used, for example, in

controlling the speed of low-power induction motors, in dimming lamps and in controlling AC

heating resistors.

Fig. 3.7 Triac

3.7 OP AMP:

An op amp is a very high gain differential amplifier with high input impedance and low output

impedance. Typical uses of the op amp are to be providing voltage amplitude changes, oscillator,

filters circuit and many type of instrumental circuit.

3.7.1 INVERTING AMPLIFIER

The Open Loop Gain of an ideal operational amplifier can be very high, as much as 1,000,000

(120dB) or more. However, this very high gain is of no real use to us as it makes the amplifier both

unstable and hard to control as the smallest of input signals, just a few micro-volts, μ would be

enough to cause the output voltage to saturate and swing towards one or the other of the voltage

supply rails losing complete control. As the open loop DC gain of an operational amplifier is

extremely high we can therefore afford to lose some of this gain by connecting a suitable resistor

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

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

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


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across the amplifier from the output terminal back to the inverting input terminal to both reduce and

control the overall gain of the amplifier. This then produces and effect known commonly

as Negative Feedback, and thus produces a very stable Operational Amplifier based system.

Negative Feedback is the process of "feeding back" a fraction of the output signal back to the input,

but to make the feedback negative, we must feed it back to the negative or "inverting input"

terminal of the op-amp using an external Feedback Resistor called Rf. This feedback connection

between the output and the inverting input terminal forces the differential input voltage towards

zero. This effect produces a closed loop circuit to the amplifier resulting in the gain of the amplifier

now being called its Closed-loop Gain. A closed-loop amplifier uses negative feedback to

accurately control the overall gain but at a cost in the reduction of the amplifiers bandwidth.

This negative feedback results in the inverting input terminal having a different signal on it than the

actual input voltage as it will be the sum of the input voltage plus the negative feedback voltage

giving it the label or term of a Summing Point. We must therefore separate the real input signal

from the inverting input by using an Input Resistor, Rin. As we are not using the positive non-

inverting input this is connected to a common ground or zero voltage terminal as shown below, but

the effect of this closed loop feedback circuit results in the voltage potential at the inverting input

being equal to that at the non-inverting input producing a Virtual Earth summing point because it

will be at the same potential as the grounded reference input. In other words, the op-amp becomes a

"differential amplifier".

3.7.2 INVERTING AMPLIFIER CONGIGURATION:

Fig 3.8 Inverting Amplifier


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In this Inverting Amplifier circuit the operational amplifier is connected with feedback to produce a

closed loop operation. For ideal op-amps there are two very important rules to remember about

inverting amplifiers, these are: "no current flows into the input terminal" and that "V1 equals V2",

(in real op-amps both these rules are broken). This is because the junction of the input and feedback

signal (X) is at the same potential as the positive (+) input which is at zero volts or ground then, the

junction is a ― irtual Earth". Because of this virtual earth node the input resistance of the amplifier

is equal to the value of the input resistor, Rin and the closed loop gain of the inverting amplifier can

be set by the ratio of the two external resistors.

We said above that there are two very important rules to remember about Inverting Amplifiers or

any operational amplifier for that matter and these are.

3.7.3 NON INVERTING AMPLIFIER:

The second basic configuration of an operational amplifier circuit is that of a Non-inverting

Amplifier. In this configuration, the input voltage signal, (Vin) is applied directly to the non-

inverting (+) input terminal which means that the output gain of the amplifier becomes "Positive" in

value in contrast to the "Inverting Amplifier" circuit whose output gain is negative in value. The

result of this is that the output signal is "in-phase" with the input signal.

Feedback control of the non-inverting amplifier is achieved by applying a small part of the output

voltage signal back to the inverting (-) input terminal via an Rf - R2 voltage divider network, again

producing negative feedback. This closed-loop configuration produces a non-inverting amplifier

circuit with very good stability, a very high input impedance, Rin approaching infinity, as no

current flows into the positive input terminal, (ideal conditions) and a low output

impedance, Rout as shown below.


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Fig. 3.9

3.7.4 OP-AMP INTEGRATOR AMPLIFIER:

An operational amplifier can be used as part of a positive or negative feedback amplifier or as an

adder or subtractor type circuit using just pure resistances in both the input and the feedback loop.

But what if we were to change the purely resistive (Rf) feedback element of an inverting amplifier

to that of a frequency dependant impedance, (Z) type complex element, such as a capacitor, C. By

replacing this feedback resistance with a capacitor we now have an RC network across the

operational amplifier producing an Op-amp Integrator circuit as shown below.

Fig 3.10 Integrator

As its name implies, the Op-amp Integrator is an operational amplifier circuit that performs the

mathematical operation of integration that is we can cause the output to respond to changes in the

input voltage over time. The integrator amplifier acts like a storage element that ―produces a

voltage output which is proportional to the integral of its input voltage with respect to time‖. In

other words the magnitude of the output signal is determined by the length of time a voltage is

http://www.electronics-tutorials.ws/capacitor/cap_1.html

http://www.electronics-tutorials.ws/rc/rc_1.html


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present at its input as the current through the feedback loop charges or discharges the capacitor as

the required negative feedback occurs through the capacitor.

When a voltage, Vin is firstly applied to the input of an integrating amplifier, the uncharged

capacitor C has very little resistance and acts a bit like a short circuit (voltage follower circuit)

giving an overall gain of less than one. No current flows into the amplifiers input and point X is a

virtual earth resulting in zero output. As the feedback capacitor C begins to charge up, its

reactance Xc decreases this results in the ratio of Xc/Rin increasing producing an output voltage

that continues to increase until the capacitor is fully charged.

At this point the capacitor acts as an open circuit, blocking anymore flow of DC current. The ratio

of feedback capacitor to input resistor (Xc/Rin) is now infinite resulting in infinite gain. The result

of this high gain (similar to the op-amps open-loop gain), is that the output of the amplifier goes

into saturation as shown below. (Saturation occurs when the output voltage of the amplifier swings

heavily to one voltage supply rail or the other with little or no control in between).

Fig 3.11

The rate at which the output voltage increases (the rate of change) is determined by the value of the

resistor and the capacitor, ―RC time constant‖. By changing this RC time constant value, either by

changing the value of the Capacitor, C or the Resistor, R, the time in which it takes the output

voltage to reach saturation can also be changed for example.


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Fig. 3.12

If we apply a constantly changing input signal such as a square wave to the input of an integrator

amplifier then the capacitor will charge and discharge in response to changes in the input signal.

This results in the output signal being that of a sawtooth waveform whose frequency is dependent

upon the RC time constant of the resistor/capacitor combination. This type of circuit is also known

as a Ramp Generator and the transfer function is given below.

Fig. 3.13

3.8 FIRING PULSE TECHNIQUE:

3.8.1 RESISTANCE TRIGGERING:

A simple firing triggering circuit is shown in fig. 3.14. the rsistance R1 limit the current through the

gate of the SCR. R2 is a variable resistance added to the circuit to achieve control over the

triggering angle of SCR. Resistor R is a stabilizing resistor. The diode D is required to ensure that

no negative voltage reaches the gate of the SCR.


28

Fig 3.14 R firing circuit and waveform

3.8.2 RESISTANCE CAPACITIVE TRIGERRING:

The capacitor C in the circuit is connected to shift the phase of the gate voltage. D1 is used to

prevent negative voltage from reaching the gate cathode of SCR.

In the negative half cycle capacitor charge to the peak negative voltage of the supply (-V) through

the diode D2. Capacitor maintains this negative voltage until supply voltage cross zero. As the

supply become positive, the capacitor charge through resistor ‗R‘ from initial voltage of –Vm to a


29

positive value. When the capacitor voltage is equal to the gate trigger voltage of the SCR, SCR is

fired and capacitor voltage is clamped to a small positive value.

Fig. 3.15. Basic idea of RC control scheme.

3.9 TRANSISTOR AS A SWITCH:

Fig. 3.16 Transistor used as a switch


30

The circuit resembles that of the common emitter. The difference is that to operate the transistor as

a switch the transistor needs to be turned either fully "OFF" (cut-off) or fully "ON" (saturated). An

ideal transistor switch would have infinite circuit resistance between the Collector and Emitter

when turned "fully-OFF" resulting in zero current flowing through it and zero resistance between

the Collector and Emitter when turned "fully-ON", resulting in maximum current flow. In practice

when the transistor is turned "OFF", small leakage currents flow through the transistor and when

fully "ON" the device has a low resistance value causing a small saturation voltage (VCE) across it.

Even though the transistor is not a perfect switch, in both the cut-off and saturation regions the

power dissipated by the transistor is at its minimum. In order for the base current to flow, the base

input terminal must be made more positive than the emitter by increasing it above the 0.7 volts

needed for a silicon device. By varying this base-emitter voltage VBE, the base current is also

altered and which in turn controls the amount of collector current flowing through the transistor as

previously discussed. When maximum collector current flows the transistor is said to be saturated.

The value of the base resistor determines how much input voltage is required and corresponding

base current to switch the transistor fully "ON".

3.10 THE 555 TIMER:

The 555 timer is an integrated circuit (chip) implementing a variety of timer and multivibrator

applications. It was produced by Signe tics Corporation in early 1970. The original name was the

SE555/NE555 and was called "The IC Time Machine". The 555 gets its name from the three 5-KΩ

resistors used in typical early implementations. It is widely used because of its ease to use, low

price and reliability.

It is one of the most popular and versatile integrated circuits which can be used to build lots of

different circuits. It includes 23 transistors, 2 diodes and 16 resistors on a silicon chip installed in an

8-pin mini dual-in-line package (DIP-8)(Refer to Figure 3.17).

The 555 Timer is a monolithic timing circuit that can produce accurate and highly stable time

delays or oscillations. The timer basically operates in one of the two modes—monostable (one-shot)

multivibrator or as an astable (free-running) multivibrator. In the monostable mode, it can produce

accurate time delays from microseconds to hours. In the astable mode, it can produce rectangular

waves with a variable duty cycle. Frequently, the 555 is used in astable mode to generate a

continuous series of pulses, but you can also use the 555 to make a one-shot or monostable circuit.


31

The 555 can source or sink 200 mA of output current, and is capable of driving wide range of

output devices. The output can drive TTL (Transistor-Transistor Logic) and has a temperature

stability of 50 parts per million (ppm) per degree Celsius change in temperature, or equivalently

0.005 %/°C.

Applications of 555 timer in monostable mode include timers, missing pulse detection, bounce free

switches, touch switches, frequency divider, capacitance measurement, pulse width modulation

(PWM) etc.

In astable or free running mode, the 555 can operate as an oscillator. The uses include LED and

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

modulation, etc. In the bistable mode, the 555 can operate as a flip-flop and is used to make

bounce-free latched switches, etc.

Refer to Figure 3.17 for the brief description of the pin connections. The pin numbers used refer to

the 8-pin mini DIP and 8-pin metal can packages. The 555 can be used with a supply voltage

(VCC) in the range 4.5 to 15V (18V absolute maximum).


32

Fig. 3.17 Functional Block Diagram of 555 Timer

The working of 555 timer is described using its functional block diagram. As shown in Figure 3.18,

the 555 timer consists of a voltage divider arrangement, two comparators, an RS flip-flop, an n-p-n

transistor Q1 and a p-n-p transistor Q2. Since the voltage divider has equal resistors, the upper

comparator has a trip point of

UTP = 2/3 Vcc

The comparator 2 has a trip point of

LTP = 1/3 Vcc

As seen in the Figure 3.18, the pin 6 (Threshold) is connected to the comparator 1. This voltage

comes from the external components (not shown). When the threshold is greater than the UTP, the


33

comparator 2 has a high output. Pin 2 (trigger) is connected to the comparator 2. This is the trigger

voltage that is used for the monostable operation of the 555 timer. When the trigger is inactive, the

trigger voltage is high. When the trigger voltage falls to less than the LTP, comparator 2 produces a

high output.

3.10.1 ASTABLE MULTIVIBRATOR:

The application of 555 timer as an astable multivibrator. An astable multivibrator is a wave-

generating circuit in which neither of the output levels is stable. The output keeps on switching

between the two unstable states and is a periodic, rectangular waveform. The circuit is therefore

known as an ‗astable multivibrator‘. lso, no external trigger is required to change the state of the

output, hence it is also called ‗free-running multivibrator‘. The time for which the output remains in

one particular state is determined by the two resistors and a capacitor externally connected to the

555 timer.

Figure 3.19 shows 555 timer connected as an astable multivibrator. Pin 5 is bypassed to ground

through a . μF capacitor. The power supply + is connected to common of pin 4 and pin 8

and pin 1 is grounded. If the output is high initially, capacitor C starts charging towards through RA

and RB. As soon as the voltage across the capacitor becomes equal to 3/2 Vcc, the upper

comparator triggers the flip-flop, and the output becomes low. The capacitor now starts discharging

through RB and transistor Q1. When the voltage across the capacitor becomes 1/3Vcc, the output of

the lower comparator triggers the flip-flop and the output becomes high. The cycle then repeats.

The output voltage and capacitor voltage waveforms are shown in Figure 3.19.

Fig. 3.18 Circuit diagram for Astable Multivibrator


34

Fig. 3.19 Output voltage waveforms

3.11 LIGHT DEPENDENT RESISTOR:

A transducer is a device that converts energy from one form to another. In the control system a

photoconductive cell is used as a transducer. Electrical conduction in semiconductor materials

occurs when free charge carrier, e.g. electrons, is available in the material and an electric field is

applied. In certain semiconductors when light energy strike on them in correct order of magnitude,

they release charge carriers.

Source Illumination chart

S.No Light Source Illumination (Lux)

1. Moonlight 0.1

2. 60W bulb at 1m 50

3. Fluorescent light 500

4. Bright sunlight 30000

This increases flow of current produced by an applied voltage. The increase of current with increase

in light intensity and the applied voltage is constant. It means that the resistance of semiconductors


35

decreases with increase the light intensity. Therefore, these semiconductors are called

photoconductive cells or photo resistors or Light Dependent Resistors (LDR), since incident light

effectively varies their resistance (Figure 2.3). In bright light the resistance of the cell can be as low

as 80 ohm. When the cell is kept in darkness its resistance is called dark resistance. At 50 LUX

(darkness) the resistance increases to over 1M ohm. The dark resistance may be as high as

× Ω.

Fig 3.22 LDR and its characteristic graph

A photoconductor has a relatively large sensitive area. A small change in light intensity causes a

large change in resistance. It is common for a photoconductive element to exhibit a resistance

change of 1000:1 for a dark to light irradiance change of 5×10-3 W/m2 to 50 W/m2. The

relationship between irradiance and resistance is, however, not linear. It is closely an exponential

relationship. The photoconductive cell suffers from a major disadvantage that temperature change

causes substantial resistance changes for a particular light intensity.

3.12 OPTOCOUPLER:

An Optocoupler, also known as an Opto-isolator or Photo-coupler, are electronic components

that interconnect two electrical circuits by means of an optical interface. The basic design of an

optocoupler consists of an LED that produces infra-red light and a semiconductor photo-sensitive


36

device that is used to detect this emitted infra-red light. Both the LED and photo-sensitive device

are enclosed in a light-tight body or package with metal legs for the electrical connections as

shown.

An optocoupler or opto-isolator consists of a light emitter, the LED and a light sensitive receiver

which can be a single photo-diode, photo-transistor, photo-resistor, photo-SCR, or a photo-TRIAC

and the basic operation of an optocoupler is very simple to understand.

Fig. 3.22

3.12.1 PHOTO-TRANSISTOR OPTOCOUPLER:

Assume a photo-transistor device as shown. Current from the source signal passes through the input

LED which emits an infra-red light whose intensity is proportional to the electrical signal. This

emitted light falls upon the base of the photo-transistor, causing it to switch-ON and conduct in a

similar way to a normal bipolar transistor. The base connection of the photo-transistor can be left

open for maximum sensitivity or connected to ground via a suitable external resistor to control the

switching sensitivity making it more stable.

When the current flowing through the LED is interrupted, the infra-red emitted light is cut-off,

causing the photo-transistor to cease conducting. The photo-transistor can be used to switch current

in the output circuit. The spectral response of the LED and the photo-sensitive device are closely

matched being separated by a transparent medium such as glass, plastic or air. Since there is no

direct electrical connection between the input and output of an optocoupler, electrical isolation up to

10kV is achieved.


37

Fig. 3.23 Photo-Transistor Optocoupler

3.12.2 OPTOCOUPLER TYPES:

Optocoupler are available in four general types, each one having an infra-red LED source but with

different photo-sensitive devices. The four optocoupler are: photo-transistor, photo-

darlington, photo-SCR and photo-triac as shown below.

Fig. 3.24


38

The photo-transistor and photo-darlington devices are mainly for use in DC circuits while the

photo-SCR and photo-triac allow AC powered circuits to be controlled. There are many other kinds

of source-sensor combinations, such as LED-photodiode, LED-LASER, lamp-photo resistor pairs,

reflective and slotted optocoupler.

Simple home made optocoupler can be constructed by using individual components. An LED and a

photo-transistor are inserted into a rigid plastic tube or encased in heat-shrinkable tubing as shown.

The tubing can be of any length.

Fig. 3.25

3.12.3 OPTOCOUPLER APPLICATIONS:

Optocoupler and opto-isolators can be used on their own, or to switch a range of other larger

electronic devices such as transistors and triacs providing the required electrical isolation between a

lower voltage control signal and the higher voltage or current output signal. Common applications

for optocoupler include microprocessor input/output switching, DC and AC power control, PC

communications, signal isolation and power supply regulation which suffer from current ground

loops, etc. The electrical signal being transmitted can be either analogue (linear) or digital (pulses).

3.12.4 OPTOCOUPLER TRIAC CONTROL:

This type of optocoupler configuration forms the basis of a very simple solid state relay application

which can be used to control any AC mains powered load such as lamps and motors. Also unlike a

thyristor (SCR), a triac is capable of conducting in both halves of the mains AC cycle with zero-

crossing detection.


39

Fig. 3.26

3.13 DC SUPPLY SYSTEM

When four diodes are connected as shown in converter circuit, the circuit is called a BRIDGE

RECTIFIER. The input to the circuit is applied to the diagonally opposite corners of the network,

and the output is taken from the remaining two corners.

One complete cycle of operation will be discussed to help you understand how this circuit works.

Let us assume the transformer is working properly and there is a positive potential at point A and a

negative potential at point B. The positive potential at point A will forward bias D3 and reverse bias

D4. The negative potential at point B will forward bias D1 and reverse bias D2. At this time D3 and

D1 are forward biased and will allow current flow to pass through them; D4 and D2 are reverse

biased and will block current flow. The path for current flow is from point B through D1, up

through RL, through D3, through the secondary of the transformer back to point B. This path is

indicated by the solid arrows. Waveforms (1) and (2) can be observed across D1 and D3.

One-half cycle later the polarity across the secondary of the transformer reverses, forward biasing

D2 and D4 and reverse biasing D1 and D3. Current flow will now be from point A through D4, up

through RL, through D2, through the secondary of T1, and back to point A. This path is indicated by

the broken arrows. Waveforms (3) and (4) can be observed across D2 and D4. You should have

noted that the current flow through RL is always in the same direction. In flowing through RL this

current develops a voltage corresponding to that shown in waveform (5). Since current flows


40

through the load (RL) during both half cycles of the applied voltage, this bridge rectifier is a full-

wave rectifier.

One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given

transformer the bridge rectifier produces a voltage output that is nearly twice that of the

conventional full-wave circuit. This may be shown by assigning values to some of the components

shown in views A and B of figure. Assume that the same transformer is used in both circuits. The

peak voltage developed between points X and Y is 1000 volts in both circuits. In the conventional

full-wave circuit shown in view A, the peak voltage from the center tap to either X or Y is 500

volts. Since only one diode can conduct at any instant, the maximum voltage that can be rectified at

any instant is 500 volts. Therefore, the maximum voltage that appears across the load resistor is

nearly - but never exceeds - 500 volts, as a result of the small voltage drop across the diode. In the

bridge rectifier shown in view B, the maximum voltage that can be rectified is the full secondary

voltage, which is 1000 volts. Therefore, the peak output voltage across the load resistor is nearly

1000 volts. With both circuits using the same transformer, the bridge rectifier circuit produces a

higher output voltage than the conventional full-wave rectifier circuit. Now output receive at a

terminal of bridge is ripple type and cannot directly use for dc supply. Now a very popular capacitor

filter circuit is used to provide constant DC output. This is a condition when no load is applied

across capacitor. When load is connected across capacitor, there is a little voltage ripple. Further

smoothing of DC output is done by various other techniques like RC filter, OP-AMP series

regulator, Series Voltage Regulator circuit etc.


41

Fig 3.27 DC Rectifier circuit

Sometime, DC output which we receive is more than the required value and need to reduce the

level. Regulator IC units contain the circuitry for reference source, comparator amplifier, control

device and overload protection all in a single IC. IC units provide regulation of either a fixed

positive voltage, a fixed negative voltage, or an adjustable set voltage.

For making DC supply circuit, we use transformer of 230V/14-014V. This type of transformer

provide center tap for neutral point (0V). Dual power supply with 12V and -12V with neutral point

is obtained. There will be instances where the currents from each supply will be unequal. In this

cause voltage is different for each supply. This cause there is a chance of development of error. The

input DC is given a voltage divider to establish a "virtual earth", and this is used as the 0V reference

for the unit to be powered. In its simplest form, it uses a pair of resistors and two additional filter

caps to make sure that the hum is within the capability of opamps to reject. There will be instances

where the currents from each supply will be unequal. Where this is the case, the resistor divider is


42

not sufficient, and the +ve and -ve voltages will be unequal. By using a cheap opamp (such as a

uA741), a DC imbalance between supplies of up to about 15mA will not cause a

problem. However, we can do better with a dual opamp (which will cost the same or less anyway),

and increase the capability for up to about 30mA of difference between the two supplies.

Fig 3.28 Circuit to produce balance neutral point

Fig 3.29 12 V dual supply


43

3.14 STREET LIGHT

A Street light, lamppost, street lamp, light standard, or lamp standard is a raised source of light on

the edge of a road or walkway, which is turned on or lit at a certain time every night. Modern lamps

may also have light-sensitive photocells to turn them on at dusk, off at dawn, or activate

automatically in dark weather. In older lighting this function would have been performed with the

aid of a solar dial. It is not uncommon for street lights to be on posts which have wires strung

between them, such as on telephone poles or utility poles.

3.14.1 LED STREET LIGHT:

An LED street light is an integrated light that uses LEDs as its light source. These are considered

integrated lights because, in most cases, the luminaire and the fixture are not separate parts (except

LED Gine-based luminaires). New in manufacturing, the LED light cluster is sealed on a panel and

then assembled to the LED panel with a heat sink to become an integrated lighting fixture.

Fig. 3.30

3.14.2 SOLAR STREET LIGHT:

Solar energy is a renewable source of energy, which is long-lasting and no pollution type. It can be

easily utilized and also a cost effective in long term. Solar street light do not need staff for

management and control and it can easily stalled in public places like hospital, school, street etc.

LED lamp is generally used because of long life and energy saving (low watt). LED street lamp is

compact and shock resistive with energy efficient. Solar street lights are raised light sources which

are powered by photovoltaic panels generally mounted on the lighting structure. The photovoltaic

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

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

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

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

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

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

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

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

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

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

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

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


44

panels charge a rechargeable battery, which powers a fluorescent or LED lamp during the night.

Various control circuit is designed which is compact and efficient.

Fig. 3.31

3.14.3 HIGH INTENSITY DISCHARGE LAMP:

High-intensity discharge lamps (HID lamps) are a type of electrical lamp which produces light by

means of an electric arc between tungsten electrodes housed inside a translucent or

transparent fused quartz or fused alumina arc tube. This tube is filled with both gas and metal salts.

The gas facilitates the arc‘s initial strike. Once the arc is started, it heats and evaporates the metal

salts forming a plasma, which greatly increases the intensity of light produced by the arc and

reduces its power consumption. High-intensity discharge lamps are a type of arc lamp.

Fig. 3.32

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

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

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

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

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

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

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

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

http://en.wikipedia.org/wiki/Plasma_(physics)

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


45

Features:

1. High efficiency -105 lm/W

2. Long life up to 24000 hrs.

3. Bright light and excellent colour rendering

4. UV control

5. Two colour temperatures: 3000K and 42000K

6. Direct replacement of high pressure sodium and Quartz Metal Halide lamp

7. High range of wattage from 20 Watt to 400 Watt

3.14.4 CONTROL OF STREET LIGHT:

Manual switch is provided on each pole of street light or a central switch is provided for series of

street light for turn On/Off. This cause extra labour is required. Generally many cities used

automatic circuit to turn On/Off. This is possible using LDR circuit which helps to switch transistor

at specific time as it resistance change and activate relay to turn circuit on.


46

CHAPTER 4 PROPOSED PROJECT WORK

Thyristor or Triac is a switching device in the medium and large power levels starting from few

kilowatts to several megawatts at voltage level of few hundred to several kilo volts levels.

BJT(Bipolar Junction Transistor) and MOSFETs (Metal Oxide Semiconductor Field Transistor)

also used as switching device at low voltage. We are working to design low cost digital firing

circuit with automatic control of firing angle according to light intensity. The circuit is designed

in such a manner so that firing circuit is active only in night (when necessary). Circuit is mainly

divided into part (1) On/Off switching circuit, (2) firing angle control circuit. Firing circuit is

divided into 10 parts as shown in fig. 4.1

Fig 4.1 Schematic Block Diagram

4.1 Synchronizing part: For producing proper firing pulse, it is necessary to synchronize the

circuit. A 220/6-0-6 V or 220/3-0-3 V 50 Hz control transformer is selected for stepping down

the 220 V supply to a low level.

Isolation &

Synchronizing block

Logic circuit

for pulse

generation

Amplification of

pulse and

isolation

LDR control circuit

(ON/OFF, and control of firing angle)

TRIAC Power


47

4.2 Cosine wave generator

One of the very popular integrator circuit using Op amp can be used to produce cosine wave.

Fig 6.2 shows integrator circuit. Signal ∫ will be obtained.

Fig 4.2 Integrator circuit

One of the problem with this type of integrator when used in practical circuit is a reduction in

output amplitude, which is not good for our circuit. For this reason another simple phase shift

circuit fig 4.3 is used and phase shift of 90 degree is set using variable resistor. For this

configuration, cosine wave at output is found for potentiometer resistance of .7 kΩ.

Fig 4.3 Phase shifting circuit


48

4.3 Comparator for producing variable width pulse

An OP AMP (LM 324) is used to realize the comparator block. The variable d.c voltage is

applied to the non-inverting terminal and cosine signal is applied at inverting terminal. Variable

voltage output is varied using simple variable pot technique. Firing angle control from 0 to 180

degree by varying variable voltage from 4.2 V to -4.2V.

Fig. 4.4 comparator circuit

4.4 Automatic Variable Voltage Generator

For automatic control of firing angle, it is necessary to make a circuit which generate variable

d.c voltage for comparator circuit according to the intensity of light (Variable voltage output

vary from -4.2 V to 4.2 V as darkness increase so, that firng angle reduce from 180 degree to 0

degree and become fix. As shown in fig 4.5, a simple instrumentation OP AMP circuit using U1,

U2, U3 is employed for this purpose. Output of instrumentation op amp is given by


49

(

)

Generally we fix and vary according to LDR resistance variation. For finding the

appropriate timing to vary firing angle, we conduct the series of test. Normal Street light On time

is noted. And conduct a test to find the resistance of LDR at evening. From the experiment we

found that LDR resistance in noon is merely Ω. During evening it resistance increase from

few kΩ to kΩ in 5 min and then sharp changing is observed. For the LDR value in between

kΩ to kΩ, the output voltage is varying from - to . . For LDR alue above kΩ,

firing is occurring at 0 degree.

Fig 4.5 Automatic Variable D.C Voltage generator using LDR


50

Circuit Implementation

Various portion of circuit is tested on MultiSim-10 before implementing it on breadboard. As per

the block diagram shown in fig 4.6, circuit is implemented in two step. Let us discuss both part

one by one.

Fig 4.6 Block diagram of implemented circuit

4.5 Automatic ON/OFF Circuit

The detail circuits diagram for the control of street light is shown in figure 4.7. The circuit

depends on a light sensitive device called LDR (light dependent resistor). The resistance of the

LDR depends on the amount of light falling on it. The simple circuit just which give a fix voltage

during evening when LDR resistance increase above 5kΩ can be used to switch transistor ON

and cause relay operate and street light start glowing. But this type of general circuit cause

frequent operation of relay during transient period. Even it damages the bulb or relay itself. For

avoiding this situation little bit complex OP AMP based circuit is used.

A set of LDR resistance reading is taken during evening and morning time. Data help us to find

the suitable operating point of this circuit. LDR resistance of 5kΩ is chosen as operating point of

relay. As shown in fig 4.7, R3, R9 and LDR formed on arm of bridge and R1 and POT formed

another arm. For the 5 kΩ resistance of LDR, voltage at port is .7 . Now by varying the

POT resistance, we set the voltage at port 2 is nearly equal to 4.74V. Terminal 1 and 2 is


51

connected to the + and – input terminal of OP AMP. As open loop gain of OP amp is 10000, for

slightly variation of input voltage, the output is either 12 V or -12 V i.e for LDR resistance of

5. kΩ, the output is . During daytime LDR resistance is always less than 5 kΩ, so output is

-12 V. this cause voltage at 3 is - . and transistor remain off. Let‘s the evening or dark

condition, in this cause LDR resistance is greater than 5 kΩ and output at OP amp is 12V and

11.3 V at terminal 3. This is able to drive transistor and operate relay and cause relay coil turn

ON.

Fig 4.7 Relay operation circuit diagram

Table 1: LDR Resistance variation graph (on 18.03.2012)


52

S.No Date Turn ON Time

1. 20.03.2012 6:38 PM

2. 21.03.2012 6:38 PM

3. 23.03.2012 6:40 PM

4. 24.03.2012 6:43 PM

Table 2: Turn ON Time of circuit

Fig 4.8 Experimental setup and circuit on PCB

4.6 TRIAC FIRING CIRCUIT

For intensity based control of street light, TRIAC is used whose firing angle change according to

the intensity. Circuit is design so that firing angle change from 130 to 0 degree for LDR

resistance change from 5 kΩ to kΩ. Fig .5 shows the Instrumentation OP amp circuit, which

generate Vref (according to light intensity) for changing firing angle automatically.


53

Firing circuit is design using Integrator, comparator and logic Gate. As in fig 4.9 , the two input

reference Vao and Vbo is taken from supply for synchronizing the circuit. Vbo is a 180 degree

phase shift from Vao. At 1 & 2, there is wave of 90 degree shift of Vao and Vbo respectively.

Vref is used to generate the specific signal at 6 & 8, which decide the firing angle. The signal at

6 & 8 is conditioned to generate firing pulse at 9 & 10 respectively for positive and negative

cycle. The signal at 11 is used as firing pulse. Optocoupler is used as isolator between power and

firing circuit.


54

Fig 4.9 Firing circuit implement in lab


55

Fig 4.10 Optocoupler interfacing circuit

Fig 4.11 Waveform at different points in the circuit of Fig4.9


56

Fig. 4.12, Firing circuit implemented on Breadboard and PCB

Fig 4.13, Firing angle Pulse observe on CRO for different LDR resistance

4.7 Change in firing angle:

Firing angle variation is observed by varying the LDR resistance. By plotting a graph between Vref

voltage apply to firing circuit and firing angle, we found that firing angle is increase with increase in LDR

resistance. So, using this graph, it is found that circuit is suitable for controlling the power of circuit

during transient period and also save energy. The ultimate aim of saving energy and automatic control

of street light is achieved.

Output voltage of Load is given by

√ √


57

Fig. 4.14 Graph for variation in firing angle with variation of Automatic Vref voltage

Fig. 4.15 graph to show Load power consumed for different firing angle for 200W lamp


58

CHAPTER 5 CONCLUSION

5.1 Summary of the work reported in the project

This project deals with the design and development of suitable control circuit, for street light

using LDR.

First, a simple circuit using comparator is design to operate the relay switch, which turns

ON/OFF the street light. The circuit has been implemented on the breadboard by selecting

suitable value of resistance in bridge. The circuit is tested to find the reliability of circuit. Firing

circuit is designed using the cosine technique. The firing angle is varying as the Vref voltage is

change and the corresponding waveform is check using CRO. By controlling the firing angle

through the LDR sensor, the power output applied to a load through Triac is controlled

automatically by controlling firing angle.

5.2 Scope of future work

The work outlined in this project leads itself to the following scope of future work through

various sensor has the potential for automatic control of AC devices like fan, load, furnaces.

1. The present work control the conventional AC circuit, but now a day LED, solar based

low power street light is used. For that type of lightning load necessary to design the DC

based Automatic controller. This possible by modifying the present circuit by using

PWM technique.

2. It is used to control the humidity of fertilizer godown. We simply connect the humidity

sensor circuit to give the Vref voltage which decide the speed of blower motor and hence

regulate the blower.

3. For maintain the temperature of furnace.


59

APPENDIX

Single Supply Quad Operational Amplifiers (LM324)

The LM324 series are low-cost, quad operational amplifiers with true differential inputs.they have

different distinct advantages over standard operational amplifier types in single supply applications.

The quad amplifier can operate at supply voltage as low as 3.0 V or as high as 32V. the common

mode input range includes the negative supply, therby eliminating the necessity for external biasing

components in many applications. The output voltage range also includes the negative power

supply voltage.

Features

1. Short circuit protected outputs

2. True differential Inputs stage

3. Single Supply Operation: 3.0 V to 32 V

4. Low Input Bias Currents: 100 nA maximum (LM324A)

5. Four OP- Amp available

6. Industry Standard Pin outs

7. Pb-Free Packages are available

Fig A.1 Pin diagram of LM324


60

QUAD two-input OR gate (SN74LS32)

A Logic OR Gate or Inclusive-OR gate is a type of digital logic gate that has an output which is

normally at logic level "0" and only goes "HIGH" to a logic level "1" when ANY of its inputs are

at logic level "1". The output of a Logic OR Gate only returns "LOW" again when ALL of its

inputs are at a logic level "0". The logic or Boolean expression given for a logic OR gate is that

for Logical Addition which is denoted by a plus sign, (+) giving us the Boolean expression

of: A+B = Q.

A simple 2-input logic OR gate can be constructed using RTL Resistor-transistor switches

connected together as shown below with the inputs connected directly to the transistor bases.

Either transistor must be saturated "ON" for an output at Q.

Fig. A.2

Logic OR Gates are available using digital circuits to produce the desired logical function and is

given a symbol whose shape represents the logical operation of the OR gate.


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Fig A.3 Pin diagram of 74LS32

QUAD two-input AND gate (SN74LS08)

A Logic AND Gate is a type of digital logic gate that has an output which is normally at logic

level "0" and only goes "HIGH" to a logic level "1" when all of its inputs are at logic level "1".

The output of a Logic AND Gate only returns "LOW" again when any of its inputs are at a logic

level "0". The logic or Boolean expression given for a logic AND gate is that for Logical

Multiplication which is denoted by a single dot or full stop symbol, (.) giving us the Boolean

expression of: A.B = Q.

A simple 2-input logic AND gate can be constructed using RTL Resistor-transistor switches

connected together as shown below with the inputs connected directly to the transistor bases.

Both transistors must be saturated "ON" for an output at Q.

Fig. A.4 AND gate circuit


62

Logic AND Gates are available using digital circuits to produce the desired logical function and

is given a symbol whose shape represents the logical operation of the AND gate.

TRIAC BT134

BT134 in a plastic envelope, intended use in application requiring high bidirectional transient

and have a blocking voltage capability and high thermal cycling performance. Typical

applications include motor control, industrial and domestic lighting, heating and static switching.

The conducting metal surface is provided for heat sink.

Repetitive Peak off state voltage……………….

RMS on state current…………………………..

Non – Repetitive Peak on- state current………. 5

Fig A.5 Pin Diagram of TRIAC BT 1


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REFRENCES

1. Tirtharaj Sen, Pijush Kanti Bhattacharjee, Member, I SIT, Manjima Bhattacharya,

―Design and Implementation of Firing ircuit for SinglePhase onverter‖, International

Journal of omputer and Electrical Engineering, ol. , No. , June

2. Wang ongqing, Hao huncheng, Zhang Suoliang,‖Design of Solar LED Street Lamp

utomatic ontrol ircuit‖, 9 International onference on Energy and Environment

Technology

3. R.W. Wall, Senior Member, IEEE, ‖Simple Methods for Detecting Zero rossing‖,

Proceedings of The 9th nnual onference of the IEEE Industrial Electronics Society

Paper # 9

4. Hengyu Wu, Minli Tang, Guo Huang,‖ Design of Multi-functional Street Light Control

System Based on AT89S52 Single-chip Microcomputer‖, nd International

Conference on Industrial Mechatronics and Automation.

5. Muhammad H. Rashid,‖Power Electronics‖, Prentice Hall of India Publishers Ltd, 9.

6. Paul B. Zbar and Albert P. Malvino, Basic Electronics: A Text – Lab Manual, 5th

edition,

Tata McGraw-Hill Publisher, 5Ω

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