venkatesh (Autosaved)

7/29/2019 venkatesh (Autosaved)

1/34

DESIGNING OF MOBILE DETECTOR

Submitted for the Partial Fulfillment of the requirements for the Award of the

Diploma in Electronics & Communication Engineering

in the Department of

Electronics AndCommunication Engineering

(2010-2013)

SUBMITTED BY

M.SANKARA RAO S.RAJESH T.RAVI KUMAR

(10294EC032) (10294EC049) (10294EC055)

B.DHARMA TEJA T.MADHU SUDHANA RAO A.V.GIRI

(10294EC011) (10294EC056) (10294EC002)

UNDER THE ESTEEMED GUIDANCE OF

Mr. G.SURESH

Asst. professor

DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

2nd Shift Polytechnic (GMRIT-294)

G.M.R. Nagar, Rajam-532101


2/34

Department of Electrical and Electronics Engineering

G.M.R. INSTITUTE OF TECHNOLOGY

G.M.R.NAGAR, RAJAM

CERTIFICATE

This is to certify that the Project report entitled LIGHT SENSITIVE

SWITCH that is being submitted by G.Venkatesh, P.Venu Kumar, S.Sravan Kumar,

D.Ravi Kumar, G.Laxman Rao, G.Tarun Kumar partial fulfilment for the award of

Diploma in Electrical and Electronics Engineering to the state board of technical education

is a record of bonafide work carried out under our guidance and supervision.

The results embodied in this report have not been submitted to any other

University or Institute for the award of any degree or diploma.

Signature of the guide signature of the head of the department

Mrs L.Lalitha Kumari , Mr. M.VENKATESWARA RAO,

Assistant Professor, Head of the Department,

Dept. of EEE Dept. of EEE

GMRIT, Rajam. GMRIT, Rajam.


3/34

3

ACKNOWLEDGEMENT

We are very much grateful to L.LALITHA KUMARI (Asst.professor) Department

of Electrical and Electronics Engineering, GMRIT, Rajam for his help, guidance and patience

she rendered to us in completion of our project successfully by providing us necessary data

technical information.

We are glad to express our sincere thanks and respect to our head of the department

Mr. M.Venkateswara Rao, Associate Professor, for supporting us in our project.

We extend our sincere gratitude to our principal Dr.C.L.V.PRASAD who has made

the atmosphere so easy to work.

Last but not the least; we thank the lab authorities of Electrical and electronics

department and everyone else who extended their help and guidance in the completion of our

project.

Sincerely,

G. VENKATESH

P. VENU KUMAR

S. SRAVAN KUMAR

D. RAVI KUMAR

G. LAXMANARAO

G. TARUN KUMAR


4/34

4

ABSTRACT

Light sensitive switch turns on street lights automatically in the evening and go off in

the morning. Is there anyone who comes early morning to turn off these lights? The followingcircuit can perform this job properly. This circuit uses the output from a simple light/dark

activated circuit and drives a ldr in its output which can be further coupled to switch on/off

an electrical appliance in a household. There is no required any person to turn on/turn off.

An appliance can be made dark or light activated by slightly changing the circuits

configuration. This idea finds numerous applications such as, automatic watering of gardens

at evening, automatic night lamp, dark activated siren and so on.

It is applicable for lighting, entrance door, automatic staircase, automatic opening of

doors to the action of a ray of light, alarm systems, etc


5/34

5

1. INTRODUCTION :

There are a wide range of applications for light sensitive switches: lighting, entrance

door, automatic staircase, automatic opening of doors to the action of a ray of light, alarm

systems, etc Many of us are familiar with photosensitive switches made with a single

transistor that is controlled by a photo resistor placed between the base and the recharger,depending on what is desired: normal functioning closed or normal open the switch.

This configuration allows easy installation more complex, involving the use of

operational amplifiers, especially those of type 741, which are very cheap. Another way to

optodetect, less known, uses a bridge assembly, which operates on the principle that when the

current is zero diagonal axle, means that the bridge is balanced.

This last principle is used in the sensitive switch installation you will be presented

next. Photocell is placed in a bridge circuit and a comparator is used as Detector Bridge

balanced. The comparators output control thyristor through a transistor. In this circuit,

protective measures must be taken because it is isolated from the network.

Power supply circuit is taken from the bridge rectifier D1D4 is filtered and

stabilized by R1, C1, and D5. The bridge circuit is difficult to identify in the given diagram,

but it is made of R2 .. R4, P1 and photo resist (LDR). IC1 is used in the comparator

configuration and power level will be about 1.8 V when potential entries vice versa

(negative) exceed that of the entry non vice versa. Resistance R5 conducts a hysteresis of

about 1V to prevent thyristor to oscillate at T1 and threshold lighting.

Switching point of the light sensitive switch may be adjusted from P1. With the

potentiometer set the minimum (minimal resistance) lamp will light a crepuscular light. Ifyou want more flexibility, replace P1 with one that has a value of 1 M. If desired operation

reverse position in the scheme of the photo resistor can be changed with the group P1/R4.

LA1 lamp will be extinguished, in this case, after dark.

Some practical advice: if you want to use higher power lamps then diodes D1 . D4

need to be replaced with other type 1N5404 and thyristor TH1 will be equipped with a heat

sink. With these changes, the circuit can control currents up to 3A.

Maximum gate for TH1 is 250 A, which means that you must use a very sensitive

thyristor. It can use any type of photo resistor. Remember precautions to be taken due to lack

of isolation mounting over the network. It is important that the entire circuit to be protected ina plastic box, of any shape, provided with a hole in the upper side, in order to allow to the

photo resistance to see. Assure that the entry cable and the exit cable are fixed. These

precautions will assure you from accidents.

1.1 OBJECTIVE OF THE PROJECT:

Main theme of this project is to control the street lamps /gaurden lamps by using LDR

and save the power wastage . There is no required any person to turn on/turn


6/34

6

1.2 Light Switch Circuit Diagram:

1.3Working of components in circuit diagram :

1. Power to the circuit is derived via the bridge rectifier d1,d2,d3 and d4.

2. Supply is smoothed and stablized by R1 , C1 and D5(zener diode).

3. IC is connected as comparator and its output voltage level will become approximately 1.8V

4. Resistor R5 creates an hysteresis of about 1v to prevent transistor and SCR .

5 .Potentiometer used for adjust the comparator switching point .

6.LDR is used for senese the darknes and bright ness .

7.SCR is used for switching operation .


7/34

7

2.1 POWER SUPPLY

INTRODUCTION

A device or system that supplies electrical or other types of energy to an output load

or group of loads is called a power supply unit or PSU. This power supply section is required

to convert the AC signal to DC signal and also to reduce the amplitude of the reduce the

amplitude of the signal. The available voltage signal from the mains is 230V/50Hz which is

an AC voltage, but the required is DC voltage (no frequency) with the amplitude of +5V and

+12V for various applications.

For switching operation 10v is fed from bridge rectifier .Rectified power is filter and

stabilize by capacitor and zener diode .

2.2 BRIDGE RECTIFIER:

A diode bridge is an arrangement of four (or more) diodes in a bridge configuration

that provides the same polarity of output for either polarity of input. When used in its most

common application, for conversion of an alternating current (AC) input into direct current a

(DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-wave

rectification from a two wire AC input, resulting in lower cost and weight as compared to a

rectifier with a 3-wire input from a transformer with a center-tapped secondary winding.

BASIC OPERATION:

When the input connected to the left corner of the diamond is positive, and the input

connected to the right corner is negative, current flows from the upper supply terminal to the

right along the red (positive) path to the output, and returns to the lower supply terminal via

the blue (negative) path.


8/34

8

When the input connected to the left corner is negative, and the input connected to

the right corner is positive, current flows from the upper supply terminal to the right along the

red (positive) path to the output, and returns to the lower supply terminal via the blue

(negative) path.

In each case, the upper right output remains positive and lower right output negative.Since this is true whether the input is AC or DC, this circuit not only produces a DC output

from an AC input, it can also provide what is sometimes called "reverse polarity protection".

The Diode :

Basic Operation :

The diode is fabricated of a semiconductor material, usually silicon, which is doped

with two impurities. One side is doped with a donor or n-type impurity which releases

electrons into the semiconductor lattice. These electrons are not bound and are free to move

about. Because there is no net charge in the donor impurity, the n-type semiconductor is

electrically neutral. The other side is doped with an acceptor or p-type impurity which

imparts free holes into the lattice. A hole is the absence of an electron which acts as a positive

charge. The p-type semiconductor is also electrically neutral because the acceptor material

adds no net charge. Figure 1(a) illustrates the cross section of the diode. The junction is the

dividing line between the n-type and p-type sides. Thermal energy causes the electrons and

holes to move randomly. Electrons diffuse across the junction into the p-type side and holes

diffuse across the junction into the n-type side. This causes a net positive charge to develop in

the n-type side and a net negative charge to develop in the p-type side. These charges set upan electric field across the junction which is directed from the n-type side to the p-type side.


9/34

9

The electric field opposes further diffusion of the electrons and holes. The region in which

the electric field exists is called the depletion region. There are no free electrons or holes in

this region because the electric field sweeps them out.

Figure 1: (a) Diode cross section. .

The polarity of the battery is such that it reinforces the electric field across the

junction causing the depletion region to widen. The positive terminal pulls electrons in the n-

type side away from the junction. The negative terminal pulls holes in the p-type side away

from the junction. No current can flow. The diode is said to be reverse biased. Figure 1(c)

shows the diode with the battery polarity reversed. The battery now tends to cancel out the

electric field in the depletion region, causing its width to decrease. The positive terminal

forces holes toward the junction. The negative terminal forces electrons toward the junction.

A current flows which increases rapidly if the applied voltage is increased. The diode is said

to be forward biased.

V-I Characteristics :

Figure 2:(b) Typical current versus voltage.

The arrow part of the symbol points in the direction of current flow when the diode is

forward biased. The upper terminal is called the anode.The lower terminal is called the

cathode. These names come from vacuum tube diodes.


10/34

10

OUTPUT SMOOTHING USING A CAPACITOR:

For many applications, especially with single phase AC where the full-wave bridge

serves to convert an AC input into a DC output, the addition of a capacitor may be desired

because the bridge alone supplies an output of fixed polarity but continuously varying or"pulsating" magnitude, an attribute commonly referred to as "ripple".

The function of this capacitor, known as a reservoir capacitor (or smoothing

capacitor) is to lessen the variation in (or 'smooth') the rectified AC output voltage waveform

from the bridge. One explanation of 'smoothing' is that the capacitor provides a low

impedance path to the AC component of the output, reducing the AC voltage across, and AC

current through, the resistive load. In less technical terms, any drop in the output voltage and

current of the bridge tends to be canceled by loss of charge in the capacitor. This charge

flows out as additional current through the load. Thus the change of load current and voltage

is reduced relative to what would occur without the capacitor. Increases of voltage

correspondingly store excess charge in the capacitor, thus moderating the change in output

voltage / current. In some designs, a series resistor at the load side of the capacitor is added.The smoothing can then be improved by adding additional stages of capacitorresistor pairs,

often done only for sub-supplies to critical high-gain circuits that tend to be In a practical

circuit, when a capacitor is directly connected to the output of a bridge, the bridge diodes

must be sized to withstand the current surge that occurs when the power is turned on at the

peak of the AC voltage and the capacitor is fully discharged. Sometimes a small series

resistor is included before the capacitor to limit this current, though in most applications the

power supply transformers resistance is already sufficient. Output can also be smoothed

using a choke and second capacitor. The choke tends to keep the current (rather than the

voltage) more constant. This design is not generally used in modern equipment due to the

high cost of an effective choke compared to a resistor and capacitor.

Capacitor Theory

Any arrangement of two conductors separated by an electric insulator (i.e.,

dielectric) is a capacitor. An electric charge deposited on one of the conductors induces an

equal charge of opposite polarity on the other conductor. As a result, an electric field exists

between the two conductor surfaces and there is a potential difference between them. The

electric field anywhere between the conductor surfaces is directly proportional to the

magnitude of the charge Q on the conductors. And the potential difference V is also directlyproportional to the charge Q. The ratio Q/V is thus a constant for any electric field


11/34

11

distribution as determined by the shape of the conductors, the distance of separation, and the

dielectric in which the field exists. The ratio Q/V is called the capacitance, C, of a particular

arrangement of conductors and dielectric. Thus, C = Q/V, where Q and V are in units of

coulomb and volt. C has the units farad (F).

CAPACITOR is an open circuit to DC. This concept is used in filtering circuit.

VOLTAGE REGULATOR:

Maintaining voltage constant at output side by zener diode. Irrespective of input

voltage output voltage remaining constant. In the circuit we maintaining 10v constant through

out circuit.

In the previousSignal Diodetutorial, we saw that a "reverse biased" diode blockscurrent in the reverse direction, but will suffer from premature breakdown or damage if the

A = Area of platesC = Capacitance (F)

D = Distance between plates (m)

a = Inner radius (m)

b = Outer radius (m)

q = Charge (Coulombs)

x = Length (m)

W = Energy (J)

r = Relative permittivity

0 = 8.85 x 10-12 F/m

D.F. = Dissipation Factor = 1/q
http://www.electronics-tutorials.ws/diode/diode_4.htmlhttp://www.electronics-tutorials.ws/diode/diode_4.htmlhttp://www.electronics-tutorials.ws/diode/diode_4.htmlhttp://www.electronics-tutorials.ws/diode/diode_4.html


12/34

12

reverse voltage applied across it is too high. However, the Zener Diode or "Breakdown

Diode" as they are sometimes called, are basically the same as the standard PN junction diode

but are specially designed to have a low pre-determined Reverse Breakdown Voltage that

takes advantage of this high reverse voltage. The point at which a zener diode breaks down or

conducts is called the "Zener Voltage" (Vz).

VI characteristics:

The Zener diode is like a general-purpose signal diode consisting of a silicon PN

junction. When biased in the forward direction it behaves just like a normal signal diode

passing the rated current, but when a reverse voltage is applied to it the reverse saturation

current remains fairly constant over a wide range of voltages. The reverse voltage increases

until the diodes breakdown voltage VB is reached at which point a process calledAvalanche

Breakdown occurs in the depletion layer and the current flowing through the zener diode

increases dramatically to the maximum circuit value (which is usually limited by a series

resistor). This breakdown voltage point is called the "zener voltage" for zener diodes.

The point at which current flows can be very accurately controlled (to less than 1%

tolerance) in the doping stage of the diodes construction giving the diode a specificzener

breakdown voltage, (Vz) ranging from a few volts up to a few hundred volts. This zener

breakdown voltage on the I-V curve is almost a vertical straight line.

The Zener Diode is used in its "reverse bias" or reverse breakdown mode, i.e. the

diodes anode connects to the negative supply. From the I-V characteristics curve above, we

can see that the zener diode has a region in its reverse bias characteristics of almost a constant

negative voltage regardless of the value of the current flowing through the diode and remains

nearly constant even with large changes in current as long as the zener diodes current remains

between the breakdown current IZ(min) and the maximum current rating IZ(max).


13/34

13

This ability to control itself can be used to great effect to regulate or stabilize a

voltage source against supply or load variations. The fact that the voltage across the diode in

the breakdown region is almost constant turns out to be an important application of the zener

diode as a voltage regulator. The function of a regulator is to provide a constant output

voltage to a load connected in parallel with it in spite of the ripples in the supply voltage or

the variation in the load current and the zener diode will continue to regulate the voltage untilthe diodes current falls below the minimum IZ(min) value in the reverse breakdown region.

The Zener Diode Regulator :

Zener Diodes can be used to produce a stabilized voltage output with low ripple

under varying load current conditions. By passing a small current through the diode from a

voltage source, via a suitable current limiting resistor (RS), the zener diode will conduct

sufficient current to maintain a voltage drop of out. We remember from the previous tutorials

that the DC output voltage from the half or full-wave rectifiers contains ripple superimposed

onto the DC voltage and that as the load value changes so to does the average output voltage.

By connecting a simple zener stabilizer circuit as shown below across the output of the

rectifier, a more stable output voltage can be produced.

The resistor, RS is connected in series with the zener diode to limit the current flowthrough the diode with the voltage source, VS being connected across the combination. The

stabilized output voltage Voutis taken from across the zener diode. The zener diode is

connected with its cathode terminal connected to the positive rail of the DC supply so it is

reverse biased and will be operating in its breakdown condition. Resistor RS is selected so to

limit the maximum current flowing in the circuit.

With no load connected to the circuit, the load current will be zero, ( IL = 0 ), and all

the circuit current passes through the zener diode which inturn dissipates its maximum power.

Also a small value of the series resistor RS will result in a greater diode current when the load

resistance RL is connected and large as this will increase the power dissipation requirement of

the diode so care must be taken when selecting the appropriate value of series resistance so


14/34

14

that the zeners maximum power rating is not exceeded under this no-load or high-impedance

condition.

The load is connected in parallel with the zener diode, so the voltage across RL is

always the same as the zener voltage, ( VR= VZ ). There is a minimum zener current for

which the stabilization of the voltage is effective and the zener current must stay above thisvalue operating under load within its breakdown region at all times.

The upper limit of current is of course dependant upon the power rating of the device.

The supply voltage VS must be greater than VZ.

One small problem with zener diode stabilizer circuits is that the diode can

sometimes generate electrical noise on top of the DC supply as it tries to stabilize the voltage.

Normally this is not a problem for most applications but the addition of a large value

decoupling capacitor across the zener output may be required to give additional smoothing.

Then to summarise a little. A zener diode is always operated in its reverse biasedcondition. A voltage regulator circuit can be designed using a zener diode to maintain a

constant DC output voltage across the load in spite of variations in the input voltage or

changes in the load current. The zener voltage regulator consists of a current limiting

resistor RS connected in series with the input voltage VS with the zener diode connected in

parallel with the load RL in this reverse biased condition. The stabilized output voltage isalways selected to be the same as the breakdown voltage VZ of the diode.

Potentiometer :

A potentiometer, also called as POT, is a 3-terminal variable resistor and is used toadjust the resistance in a circuit.

Potentiometers work by having a resistive element inside. Both end terminals are

attached to it, and do not move. The wiper travels along the strip when the knob is turned.

The closer the wiper is to the end terminal it is wired in conjunction with, the less the

resistance, because the path of the current will be shorter. The further away it moves from the

terminal, the greater the resistance will be.

The symbol for a potentiometer is the same one as a resistor, save for an arrow in the

middle. In a circuit where they are used strictly as variable resistors or rheostats, only twoterminals are wired to the other components. All three terminals are wired separately when

they function as voltage dividers. Light dimmers in houses and volume controls on

electronics are two common applications. Others include switches and position sensors.


15/34

15

TRANSISTOR :

The first solid-state device discussed was the two-element semiconductor diode. The

next device on our list is even more unique. It not only has one more element than the diode

but it can amplify as well. Semiconductor devices that have-three or more elements are called

TRANSISTORS. The term transistor was derived from the words TRANSfer and resISTOR.

This term was adopted because it best describes the peration of the transistor - the transfer of

an input signal current from a low-resistance circuit to a high-resistance circuit. Basically, the

transistor is a solid-state device that amplifies by controlling the flow of current carriersthrough its semiconductor materials.

There are many different types of transistors, but their basic theory of operation is all

the same. As a matter of fact, the theory we will be using to explain the operation of a

transistor is the same theory used earlier with the PN-junction diode except that now two

such junctions are required to form the three elements of a transistor. The three elements of

the two-junction transistor are (1) the EMITTER, which gives off, or emits," current carriers

(electrons or holes); (2) the BASE, which controls the flow of current carriers; and (3) the

COLLECTOR, which collects the current carriers.

CLASSIFICATION :

Transistors are classified as either NPN or PNP according to the arrangement of their

N and P materials. Their basic construction and chemical treatment is implied by their

names, "NPN" or "PNP." That is, an NPN transistor is formed by introducing a thin region of

P-type material between two regions of N-type material. On the other hand, a PNP transistor

is formed by introducing a thin region of N-type material between two regions of P-type

material.

Transistors constructed in this manner have two PN junctions, as shown in figure 2-2.

One PNjunction is between the emitter and the base; the other PN junction is between the
http://images.brighthub.com/21/0/210916CA565329F64BC6C7C1DE09D39C85B4161C_large.jpg


16/34

16

collectorand the base. The two junctions share one section of semiconductor material so that

the transistor actually consists of three elements.

Figure 2-2.Transistor block diagrams.

Since the majority and minority current carriers are different for N and P materials, it

stands to reason that the internal operation of the NPN and PNP transistors will also be

different. The theory of operation of the NPN and PNP transistors will be discussed

separately in the next few paragraphs. Any additional information about the PN junction will

be given as the theory of transistor operation is developed. To prepare you for the

forthcoming information, the two basic types of transistors along with their circuit symbols

are shown in figure 2-3. It should be noted that the two symbols are different. The horizontal

line represents the base, the angular line with the arrow on it represents the emitter, and theother angular line represents the collector. The direction of the arrow on the emitter

distinguishes the NPN from the PNP transistor. If the arrow points in, (Points iN) the

transistor is a PNP. On the other hand if the arrow points out, the transistor is an NPN (Not

Pointing iN).


17/34

17

Figure 2-3.Transistor representations.

Another point you should keep in mind is that the arrow always points in the direction

of hole flow, or from the P to N sections, no matter whether the P section is the emitter or

base. On the other hand, electron flow is always toward or against the arrow, just like in the

junction diode.

TRANSISTOR THEORY :

You should recall from an earlier discussion that a forward-biased PN junction is

comparable to a low-resistance circuit element because it passes a high current for a given

voltage. In turn, a reverse-biased PN junction is comparable to a high-resistance circuit

element. By using the Ohm's law formula for power (P = I2R) and assuming current is held

constant, you can conclude that the power developed across a high resistance is greater than

that developed across a low resistance. Thus, if a crystal were to contain two PN junctions

(one forward-biased and the other reverse-biased), a low-power signal could be injected into

the forward-biased junction and produce a high-power signal at the reverse-biased junction.In this manner, a power gain would be obtained across the crystal. This concept, which is

merely an extension of the material covered in chapter 1, is the basic theory behind how the

transistor amplifies. With this information fresh in your mind, let's proceed directly to the

NPN transistor.

NPN Transistor Operation :

Just as in the case of the PN junction diode, the N material comprising the two end

sections of the NP N transistor contains a number of free electrons, while the center P section

contains an excess number of holes. The action at each junction between these sections is thesame as that previously described for the diode; that is, depletion regions develop and the


18/34

18

junction barrier appears. To use the transistor as an amplifier, each of these junctions must be

modified by some external bias voltage. For the transistor to function in this capacity, the first

PN junction (emitter-base junction) is biased in the forward, or low-resistance, direction. At

the same time the second PN junction (base-collector junction) is biased in the reverse, or

high-resistance, direction. A simple way to remember how to properly bias a transistor is to

observe the NPN or PNP elements that make up the transistor. The letters of these elementsindicate what polarity voltage to use for correct bias. For instance, notice the NPN transistor

below:

1. The emitter, which is the first letter in the NPN sequence, is connected to the negative side

of the

battery while the base, which is the second letter (NPN), is connected to the positive side.

2. However, since the second PN junction is required to be reverse biased for propertransistor operation, the collector must be connected to an opposite polarity voltage (positive)

than that indicated by its letter designation(NPN). The voltage on the collector must also be

more positive than the base, as shown below:


19/34

19

We now have a properly biased NPN transistor. In summary, the base of the NPN

transistor must be positive with respect to the emitter, and the collector must be more positive

than the base.

NPN FORWARD-BIASED JUNCTION :

An important point to bring out at this time, which was not necessarily mentioned

during the explanation of the diode, is the fact that the N material on one side of the forward-

biased junction is more heavily doped than the P material. This results in more current being

carried across the junction by the majority carrier electrons from the N material than the

majority carrier holes from the P material. Therefore, conduction through the forward-biased

junction, as shown in figure 2-5, is mainly by majority carrier electrons from the N material

(emitter).

Figure 2-5.The forward-biased junction in an NPN transistor.

With the emitter-to-base junction in the figure biased in the forward direction,

electrons leave the negative terminal of the battery and enter the N material (emitter). Since

electrons are majority current carriers in the N material, they pass easily through the emitter,

cross over the junction, and combine with holes in the P material (base). For each electron

that fills a hole in the P material, another electron will leave the P material (creating a newhole) and enter the positive terminal of the battery.

NPN REVERSE-BIASED JUNCTION :

The second PN junction (base-to-collector), or reverse-biased junction as it is called

(fig. 2-6), blocks the majority current carriers from crossing the junction. However, there is a

very small current, mentioned earlier, that does pass through this junction. This current is

called minority current, or reverse current. As you recall, this current was produced by the

electron-hole pairs. The minority carriers for the reverse-biased PN junction are the electrons

in the P material and the holes in the N material. These minority carriers actually conduct the

current for the reverse-biased junction when electrons from the P material enter the Nmaterial, and the holes from the N material enter the P material. However, the minority


20/34

20

current electrons (as you will see later) play the most important part in the operation of the

NPN transistor.

Figure 2-6.The reverse-biased junction in an NPN transistor.

At this point you may wonder why the second PN junction (base-to-collector) is not

forward biased like the first PN junction (emitter-to-base). If both junctions were forward

biased, the electrons would have a tendency to flow from each end section of the N P N

transistor (emitter and collector) to the center P section (base). In essence, we would have

two junction diodes possessing a common base, thus eliminating any amplification and

defeating the purpose of the transistor. A word of caution is in order at this time. If you

should mistakenly bias the second PN junction in the forward direction, the excessive current

could develop enough heat to destroy the junctions, making the transistor useless. Therefore,be sure your bias voltage polarities are correct before making any electrical connections.

PNP Transistor Operation :

The PNP transistor works essentially the same as the NPN transistor. However, since

the emitter, base, and collector in the PNP transistor are made of materials that are different

from those used in the NPN transistor, different current carriers flow in the PNP unit. The

majority current carriers in the PNP transistor are holes. This is in contrast to the NPN

transistor where the majority current carriers are electrons. To support this different type of

current (hole flow), the bias batteries are reversed for the PNP transistor. A typical bias setupfor the PNP transistor is shown in figure 2-8. Notice that the procedure used earlier to

properly bias the NPN transistor also applies here to the PNP transistor. The first letter (P) in

the PNP sequence indicates the polarity of the voltage required for the emitter (positive), and

the second letter (N) indicates the polarity of the base voltage (negative). Since the base-

collector junction is always reverse biased, then the opposite polarity voltage (negative) must

be used for the collector. Thus, the base of the PNP transistor must be negative with respect

to the emitter, and the collector must be more negative than the base. Remember, just as in

the case of the NPN transistor, this difference in supply voltage is necessary to have current

flow (hole flow in the case of the PNP transistor) from the emitter to the collector. Although

hole flow is the predominant type of current flow in the PNP transistor, hole flow only takes

place within the transistor itself, while electrons flow in the external circuit. However, it is


21/34

21

the internal hole flow that leads to electron flow in the external wires connected to the

transistor.

Figure 2-8.A properly biased PNP transistor.

PNP FORWARD-BIASED JUNCTION. :

Now let us consider what happens when the emitter-base junction in figure 2-9 isforward biased. With the bias setup shown, the positive terminal of the battery repels the

emitter holes toward the base, while the negative terminal drives the base electrons toward

the emitter. When an emitter hole and a base electron meet, they combine. For each electron

that combines with a hole, another electron leaves the negative terminal of the battery, and

enters the base. At the same time, an electron leaves the emitter, creating a new hole, and

enters the positive terminal of the battery. This movement of electrons into the base and out

of the emitter constitutes base current flow (IB), and the path these electrons take is referred

to as the emitter-base circuit.

Figure 2-9.

The forward-biased junction in a PNP transistor.


22/34

22

PNP REVERSE-BIASED JUNCTION. :

In the reverse-biased junction (fig. 2-10), the negative voltage on the collector and the

positive voltage on the base block the majority current carriers from crossing the junction.

However, this same negative collector voltage acts as forward bias for the minority currentholes in the base, which cross the junction and enter the collector. The minority current

electrons in the collector also sense forward bias-the positive base voltage-and move into the

base. The holes in the collector are filled by electrons that flow from the negative terminal of

the battery. At the same time the electrons leave the negative terminal of the battery, other

electrons in the base break their covalent bonds and enter the positive terminal of the battery.

Although there is only minority current flow in the reverse-biased junction, it is still very

small because of the limited number of minority current carriers.

Figure 2-10.The reverse-biased junction in a PNP transistor.

TRANSISTOR CONFIGURATIONS :

A transistor may be connected in any one of three basic configurations (fig. 2-16):

common emitter (CE), common base (CB), and common collector (CC). The term common is

used to denote the element that is common to both input and output circuits. Because the

common element is often grounded, these configurations are frequently referred to as

grounded emitter, grounded base, and grounded collector.


23/34

23

Figure 2-16.Transistor configurations.

Each configuration, as you will see later, has particular characteristics that make it

suitable for specific applications. An easy way to identify a specific transistor configuration

is to follow three simple steps:

1. Identify the element (emitter, base, or collector) to which the input signal is applied.

2. Identify the element (emitter, base, or collector) from which the output signal is taken.

3. The remaining element is the common element, and gives the configuration its name.

Therefore, by applying these three simple steps to the circuit in figure 2-12, we can

conclude that this circuit is more than just a basic transistor amplifier. It is a common-emitter

amplifier.

Common Emitter :

The common-emitter configuration (CE) shown in figure 2-16 view A is the

arrangement most frequently used in practical amplifier circuits, since it provides good

voltage, current, and power gain. The common emitter also has a somewhat low input

resistance (500 ohms-1500 ohms), because the input is applied to the forward-biased

junction, and a moderately high output resistance (30 kilohms-50 kilohms or more), because

the output is taken off the reverse-biased junction. Since the input signal is applied to the

base-emitter circuit and the output is taken from the collector-emitter circuit, the emitter is

the element common to both input and output.


24/34

24

Since you have already covered what you now know to be a common-emitter

amplifier (fig. 2-12), let's take a few minutes and review its operation, using the PNP

common-emitter configuration shown in figure 2-16 view A.

When a transistor is connected in a common-emitter configuration, the input signal is

injected between the base and emitter, which is a low resistance, low-current circuit. As theinput signal swings positive, it also causes the base to swing positive with respect to the

emitter. This action decreases forward bias which reduces collector current (IC) and increases

collector voltage (making VC more negative). During the negative alternation of the input

signal, the base is driven more negative with respect to the emitter. This increases forward

bias and allows more current carriers to be released from the emitter, which results in an

increase in collector current and a decrease in collector voltage (making VC less negative or

swing in a positive direction). The collector current that flows through the high resistance

reverse-biased junction also flows through a high resistance load (not shown), resulting in a

high level of amplification.

Since the input signal to the common emitter goes positive when the output goesnegative, the two signals (input and output) are 180 degrees out of phase. The common-

emitter circuit is the only configuration that provides a phase reversal.

The common-emitter is the most popular of the three transistor configurations because

it has the best combination of current and voltage gain. The term GAINis used to describe the

amplification capabilities of the amplifier. It is basically a ratio of output versus input. Each

transistor configuration gives a different value of gain even though the same transistor is

used. The transistor configuration used is a matter of design consideration. However, as a

technician you will become interested in this output versus input ratio (gain) to determine

whether or not the transistor is working properly in the circuit.

Common Base ;

The common-base configuration (CB) shown in figure 2-16, view B is mainly used

for impedance matching, since it has a low input resistance (30 ohms-160 ohms) and a high

output resistance (250 kilohms-550 kilohms). However, two factors limit its usefulness in

some circuit applications: (1) its low input resistance and (2) its current gain of less than 1.

Since the CB configuration will give voltage amplification, there are some additional

applications, which require both a low-input resistance and voltage amplification, that could

use a circuit configuration of this type; for example, some microphone amplifiers.

In the common-base configuration, the input signal is applied to the emitter, the

output is taken from the collector, and the base is the element common to both input and

output. Since the input is applied to the emitter, it causes the emitter-base junction to react in

the same manner as it did in the common-emitter circuit. For example, an input that aids the

bias will increase transistor current, and one that opposes the bias will decrease transistor

current.

Unlike the common-emitter circuit, the input and output signals in the common-base

circuit are in phase. To illustrate this point, assume the input to the PNP version of the

common-base circuit in figure 2-16 view B is positive. The signal adds to the forward bias,

since it is applied to the emitter, causing the collector current to increase. This increase in Icresults in a greater voltage drop across the load resistor RL (not shown), thus lowering the


25/34

25

collector voltage V C. The collector voltage, in becoming less negative, is swinging in a

positive direction, and is therefore in phase with the incoming positive signal.

.

Common Collector :

The common-collector configuration (CC) shown in figure 2-16 view C is used

mostly for impedance matching. It is also used as a current driver, because of its substantial

current gain. It is particularly useful in switching circuitry, since it has the ability to pass

signals in either direction (bilateral operation).

In the common-collector circuit, the input signal is applied to the base, the output is

taken from the emitter, and the collector is the element common to both input and output. The

common collector is equivalent to our old friend the electron-tube cathode follower. Both

have high input and low output resistance. The input resistance for the common collector

ranges from 2 kilohms to 500 kilohms, and the output resistance varies from 50 ohms to 1500

ohms. The current gain is higher than that in the common emitter, but it has a lower powergain than either the common base or common emitter. Like the common base, the output

signal from the common collector is in phase with the input signal. The common collector is

also referred to as an emitter-follower because the output developed on the emitter follows

the input signal applied to the base.

OP AMP :

Circuit notation: -

Circuit diagram symbol for an op-amp
http://en.wikipedia.org/wiki/File:Op-amp_symbol.svghttp://en.wikipedia.org/wiki/File:Op-amp_symbol.svghttp://en.wikipedia.org/wiki/File:Op-amp_symbol.svghttp://en.wikipedia.org/wiki/File:Op-amp_symbol.svg


26/34

26

V+: non-inverting input V: inverting input Vout: output VS+: positive power supply VS: negative power supply

The power supply pins (VS+ and VS) can be labeled in different ways (See IC power

supply pins). Despite different labeling, the function remains the sameto provide additional

power for amplification of the signal. Often these pins are left out of the diagram for clarity,

and the power configuration is described or assumed from the circuit.

Operation: - As a comparator

An op-amp without negative feedback :

The amplifier's differential inputs consist of a V+ input and a V input, and ideally the

op-amp amplifies only the difference in voltage between the two, which is called the

differential input voltage. The output voltage of the op-amp is given by the equation,

Where V+ is the voltage at the non-inverting terminal, V is the voltage at the inverting

terminal and AOL is the open-loop gain of the amplifier (the term "open-loop" refers to the

absence of a feedback loop from the output to the input).

The magnitude ofAOL is typically very large10,000 or more for integrated circuit

op-ampsand therefore even a quite small difference between V+ and V drives the amplifier

output nearly to the supply voltage. This is called saturation of the amplifier. The magnitude

ofAOL is not well controlled by the manufacturing process, and so it is impractical to use an

operational amplifier as a stand-alone differential amplifier. Without negative feedback, and

perhaps with positive feedback for regeneration, an op-amp acts as a comparator. If the

inverting input is held at ground (0 V) directly or by a resistor, and the input voltage V in

applied to the non-inverting input is positive, the output will be maximum positive; if V in is

negative, the output will be maximum negative. Since there is no feedback from the output to
http://en.wikipedia.org/wiki/IC_power_supply_pinshttp://en.wikipedia.org/wiki/IC_power_supply_pinshttp://en.wikipedia.org/wiki/IC_power_supply_pinshttp://en.wikipedia.org/wiki/Electronic_feedback_loopshttp://en.wikipedia.org/wiki/Differential_amplifierhttp://en.wikipedia.org/wiki/Negative_feedback_amplifierhttp://en.wikipedia.org/wiki/Positive_feedbackhttp://en.wikipedia.org/wiki/Regenerative_circuithttp://en.wikipedia.org/wiki/Comparatorhttp://en.wikipedia.org/wiki/File:Op-amp_open-loop_1.svghttp://en.wikipedia.org/wiki/Comparatorhttp://en.wikipedia.org/wiki/Regenerative_circuithttp://en.wikipedia.org/wiki/Positive_feedbackhttp://en.wikipedia.org/wiki/Negative_feedback_amplifierhttp://en.wikipedia.org/wiki/Differential_amplifierhttp://en.wikipedia.org/wiki/Electronic_feedback_loopshttp://en.wikipedia.org/wiki/IC_power_supply_pinshttp://en.wikipedia.org/wiki/IC_power_supply_pins


27/34

27

either input, this is anopen loopcircuit acting as a comparator. The circuit's gain is just the

AOL< of the op-amp.

As a non-inverting amplifier

An op-amp with negative feedback :

If the output voltage to the inverting input. The closed loop feedback greatly reduces

the gain of the amplifier. If negative feedback is used, the circuit's overall gain and other

parameters become determined more by the feedback network than by the op-amp itself. If

the feedback network is made of components with relatively constant, stable values, the

unpredictability and inconstancy of the op-amp's parameters do not seriously affect the

circuit's performance. Typically the op-amp's very large gain is controlled by negative

feedback, which largely determines the magnitude of its output ("closed-loop") voltage gain

in amplifier applications, or the transfer function required (in analog computers). High inputimpedance at the input terminals and low output impedance at the output terminal(s) are

important typical characteristics.

For example, in a non-inverting amplifier (see the figure on the right) adding a

negative feedback via the voltage divider Rf, Rg reduces the gain. Equilibrium will be

established when Vout is just sufficient to reach around and "pull" the inverting input to the

same voltage as Vin. The voltage gain of the entire circuit is determined by 1 + Rf/Rg. As a

simple example, if Vin= 1V and Rf = Rg, Voutwill be 2V, the amount required to keep V at

1V. Because of the feedback provided by Rf, Rg this is a closed loop circuit. Its overall gain

Vout / Vin is called the closed-loop gainACL. Because the feedback is negative, in this case

ACL is less than theAOL of the op-amp.

Another way of looking at it is to make two relatively valid assumptions: One, that

when an op-amp is being operated in linear mode, the difference in voltage between the non-

inverting (+) pin and the inverting (-) pin is so small as to be considered negligible.The

second assumption is that the input impedance at both + and - pins is extremely high (at least

several mega ohms with modern op-amps). Thus, when the circuit to the right is operated as a

non-inverting linear amplifier, Vin will appear at the + and - pins and create a current i

through Rg equal to Vin/Rg. Since Kirchhoffs current law states that the same current mustleave a node as enter it, and since the impedance into the - pin is near infinity, we can assume
http://en.wikipedia.org/wiki/Electronic_feedback_loopshttp://en.wikipedia.org/wiki/Electronic_feedback_loopshttp://en.wikipedia.org/wiki/Electronic_feedback_loopshttp://en.wikipedia.org/wiki/Comparatorhttp://en.wikipedia.org/wiki/Transfer_functionhttp://en.wikipedia.org/wiki/Analog_computershttp://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/File:Operational_amplifier_noninverting.svghttp://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/Analog_computershttp://en.wikipedia.org/wiki/Transfer_functionhttp://en.wikipedia.org/wiki/Comparatorhttp://en.wikipedia.org/wiki/Electronic_feedback_loops


28/34

28

the overwhelming majority of the same current i travels through Rf, creating an output

voltage equal to Vin + i*Rf. By combining terms, we can easily determine the gain of this

particular type of circuit.

Op-amp characteristics :

Ideal op-amps

An equivalent circuit of an operational amplifier that models some resistive non-ideal

parameters.

I. The output attempts to do whatever is necessary to make the voltage difference

between the inputs zero.

II. The inputs draw no current.

The first rule only applies in the usual case where the op-amp is used in a closed-loop

design (negative feedback, where there is a signal path of some sort feeding back from the

output to the inverting input). These rules are commonly used as a good first approximation

for analyzing or designing op-amp circuits.

In practice, none of these ideals can be perfectly realized, and various shortcomings

and compromises have to be accepted. Depending on the parameters of interest, a real op-amp may be modeled to take account of some of the non-infinite or non-zero parameters

using equivalent resistors and capacitors in the op-amp model. The designer can then include

the effects of these undesirable, but real, effects into the overall performance of the final

circuit. Some parameters may turn out to have negligible effect.
http://en.wikipedia.org/wiki/Negligiblehttp://en.wikipedia.org/wiki/File:Op-Amp_Internal.svghttp://en.wikipedia.org/wiki/Negligible


29/34

29

Pin diagram explanation :

Definition of 741-pin functions:

Pin 1 (Offset Null): Offset nulling, see Fig. 11. Since the op-amp is the differential type,

input offset voltage must be controlled so as to minimize offset. Offset voltage is nulled by

application of a voltage of opposite polarity to the offset. An offset null-adjustment

potentiometer may be used to compensate for offset voltage. The null-offset potentiometer

also compensates for irregularities in the operational amplifier manufacturing process which

may cause an offset. Consequently, the null potentiometer is recommended for critical

applications. See 'Offset Null Adjustment' for method.

Pin 2 (Inverted Input): All input signals at this pin will be inverted at output pin 6. Pins 2

and 3 are very important (obviously) to get the correct input signals or the op amp can not do

its work.

Pin 3 (Non-Inverted Input): All input signals at this pin will be processed normally without

inversion.The rest is the same as pin 2.

Pin 4 (-V): The V- pin (also referred to as Vs.) is the negative supply voltage terminal.

Supply-voltage operating range for the 741 is -4.5 volts (minimum) to -18 volts (max), and itis specified for operation between -5 and -15 Vdc. The device will operate essentially the


30/34

30

same over this range of voltages without change in timing period. Sensitivity of time interval

to supply voltage change is low, typically 0.1% per volt. (Note: Do not confuse the -V with

ground).

Pin5 (Offset Null): See pin 1, and Fig. 11.

Pin 6 (Output): Output signal's polarity will be the opposite of the input's when this signal

is applied to the op-amp's inverting input. For example, a sine-wave at the inverting input will

output a square-wave in the case of an inverting comparator circuit.

Pin 7 (posV): The V+ pin (also referred to as Vcc) is the positive supply voltage terminal of

the 741 Op-Amp IC. Supply-voltage operating range for the 741 is +4.5 volts (minimum) to

+18 volts (maximum), and it is specified for operation between +5 and +15 Vdc. The device

will operate essentially the same over this range of voltages without change in timing period.

Actually, the most significant operational difference is the output drive capability, which

increases for both current and voltage range as the supply voltage is increased. Sensitivity of

time interval to supply voltage change is low, typically 0.1% per volt.

Pin 8 (N/C): The 'N/C' stands for 'Not Connected'. There is no other explanation. There is

nothing connected to this pin, it is just there to make it a standard 8-pin package.

THYRISTORSCR :


31/34

31

The bistable action of thyristors is readily explained byanalysis of the structure of an

SCR. This analysis isessentially the same for any operating quadrant of triacbecause a triac

may be considered as two parallel SCRsoriented in opposite directions. Figure 2.1(a) shows

the schematic symbol for an SCR, and Figure 2.1(b) showsthe PNPN structure the

symbol represents. In thetwotransistor model for the SCR shown in Figure 2.1(c),the

interconnections of the two transistors are such thatregenerative action occurs. Observe that if

current is injected into any leg of the model, the gain of thetransistors (if sufficiently high)

causes this current to beamplified in another leg. In order for regeneration to occur, it is

necessary for the sum of the common base current gains () of the two transistors to exceed

unity.

Therefore, because the junction leakage currents are relatively small and current gain

is designed to be low at the leakage current level, the PNPN device remains off unless

external current is applied. When sufficient trigger current is applied (to the gate, for

example, in the case of an SCR) to raise the loop gain to unity, regeneration occurs and the

onstate principal current is limited primarily by external circuit impedance. If the initiating

trigger current is removed, the thyristor remains in the on state, providing the current level is

high enough to meet the unity gain criteria. This critical current is called latching current.In

order to turn off a thyristor, some change in current must occur to reduce the loop gain below

unity. From the model, it appears that shorting the gate to cathode would accomplish this.

However in an actual SCR structure, the gate area is only a fraction of the cathode

area and very little current is diverted by the short. In practice, the principal current must be

reduced below a certain level, called holding current, before gain falls below unity and

turnoff may commence. In fabricating practical SCRs and Triacs, a shorted emitter design

is generally used in which, schematically, a resistor is added from gate to cathode or gate to

MT1. Because current is diverted from the Nbase through theresistor, the gate trigger

current, latching current and holding current all increase. One of the principal reasons for the

shunt resistance is to improve dynamic performance at high temperatures. Without the shunt,

leakage current on most high current thyristors could initiate turnon at high temperatures.


32/34

32

Sensitive gate thyristors employ a high resistance shunt or none at all; consequently,

their chsaracteristics can be altered dramatically by use of an external resistance. An external

resistance has a minor effect on most shorted emitter designs.

Junction temperature is the primary variable affecting thyristor characteristics.

Increased temperatures make the thyristor easier to turn on and keep on. Consequently,circuit conditions which determine turnon must be designed to operate at the lowest

anticipated junction temperatures, while circuit conditions which are to turn off the thyristor

or prevent false triggering must be designed to operate at the maximum junction temperature.

Thyristor specifications are usually written with case temperatures specified and with

electrical conditions such that the power dissipation is low enough that the junction

temperature essentially equals the case temperature. It is incumbent upon the user to properly

account for changes in characteristics caused by the circuit operating conditions different

from the test conditions.

TRIGGERING CHARACTERISTICS ;

Turnon of a thyristor requires injection of current to raise the loop gain to unity. The

current can take the form of current applied to the gate, an anode current resulting from

leakage, or avalanche breakdown of a blocking junction. As a result, the breakover voltage of

a thyristor can be varied or controlled by injection of a current at the gate terminal. Figure 2.2

shows the interaction of gate current and voltage for an SCR. When the gate current Ig is

zero, the applied voltage must reach the breakover voltage of the SCR before switching

occurs. As the value of gate current is increased, however, the ability of a thyristor to support

applied voltage is reduced and there is a certain value of gate current at which the behavior of

the thyristor closely resembles that of a rectifier. Because thyristor turnon, as a result ofexceeding the breakover voltage, can produce high instantaneous power dissipation

nonuniformly distributed over the die area during the switching transition, extreme

temperatures resulting in die failure may occur unless the magnitude and rate of rise of

principal current (di/dt) is restricted to tolerable levels.

For normal operation, therefore, SCRs and triacs are operated at applied voltages

lower than the breakover voltage, and are made to switch to the on state by gate signals high

enough to assure complete turnon independent of the applied voltage. On the other hand,

diacs and other thyristor trigger devices are designed to be triggered by anode breakover.

Nevertheless they also have di/dt and peak current limits which must be adhered to. A triac

works the same general way for both positive and negative voltage. However since a triac canbe switched on by either polarity of the gate signal regardless of the voltage polarity across

the main terminals, the situation is somewhat more complex than for an SCR. The various

combinations of gate and main terminal polarities are shown in Figure 2.3. The relative

sensitivity depends on the physical structure of a particular triac, but as a rule, sensitivity is

highest in quadrant I and quadrant IV is generally considerably less sensitive than the others.

RESISTORS :

Resistance is measured in terms of units called "Ohms" (volts per ampere), which is

commonly abbreviated with the Greek letter . Ohms are also used to measure the quantities

of impedance and reactance, as described in a later chapter. The variable most commonly

used to represent resistance is "r" or "R".


33/34

33

Resistance is defined as:

where is the resistivity of the material, L is the length of the resistor, and A is the cross -

sectional area of the resistor.

we can relate the values R, V, and I with the following equation:

V=R *I


34/34

venkatesh (Autosaved)

Documents

Transcript of venkatesh (Autosaved)