Motor Burnout and Under voltage protection

1
MOTOR BURNOUT AND UNDER-VOLTAGE
Protection
A PROJECT REPORT
Submitted by
Rahul Kundu 11901612071
Saurav Ghosh 11901612090
Soumik Bakshi 11901612099
Sourav Ghosh 11901612101
In partial fulfilment for the award of the degree
Of
BACHELOR OF TECHNOLOGY
IN
ELECTRICAL ENGINEERING
UNDER THE GUIDANCE
OF
MR. INDRAJIT KOLEY
ASST. PROFESSOR, DEPT. OF ELECTRICAL ENGINEERING
SILIGURI INSTITUTE OF TECHNOLOGY
(A unit by TECHNO INDIA GROUP
approved by AICTE & affiliated to WBUT)
Sukna , Siliguri-734009, West Bengal
JUNE 2016

2
ACKNOWLEDGEMENT
It has been a great experience for us to do such an exciting work. This opportunity has
been rendered to us by faculty members of Electrical Engineering Department of our college
Siliguri Institute of Technology. We are grateful to them for their obligation.
We would like to express our immense gratitude to the respective Head of the
Department of Electrical Engineering MR.JAYANTA BHUSAN BASU, this work wouldn’t
have been completed without the expert guidance and help from our project guide MR.
INDRAJIT KOLEY. We convey our earnest gratitude towards him for his effort.
__________________
Rahul Kundu
Roll No.11901612071
__________________
Saurav Ghosh
Roll No.11901612090
__________________
Soumik Bakshi
Roll No.11901612099
_________________
Sourav Ghosh
RollNo.11901612101

3
DECLARATION
We declare that this written submission represents our ideas in our own words and where
others' ideas or words have been included, we have adequately cited and referenced the
original sources. We also declare that we have adhered to all principles of academic honesty
and integrity and have not misrepresented or fabricated or falsified any idea/data/fact/source
in my submission. We understand that any violation of the above will be cause for
disciplinary action by the Institute and can also evoke penal action from the sources which
have thus not been properly cited or from whom proper permission has not been taken when
needed.
__________________
Rahul Kundu
Roll No.11901612071
__________________
Saurav Ghosh
Roll No.11901612090
__________________
Soumik Bakshi
Roll No.11901612099
_________________
Sourav Ghosh
RollNo.11901612101

4
SILIGURI INSTITUTE OF TECHNOLOGY
SILIGURI -734009
WEST BENGAL UNIVERSITY OF TECHNOLOGY
KOLKATA - 700064
BONAFIDE CERTIFICATE
Certified that this project synopsis “MOTOR BURN OUT AND UNDERVOLTAGE
PROTECTION” is the bonafide work of “RAHUL KUNDU, SAURAV GHOSH,
SOUMIK BAKSHI, SOURAV GHOSH” working under my supervision.
___________________________
JAYANTA BHUSAN BASU
HEAD OF THE DEPARTMENT
Electrical Engineering Department
_________________________
INDRAJIT KOLEY
ASSISTANT PROFESSOR
Electrical Engineering Department

5
ABSTRACT
This Under-voltage protection circuit is a reliable and low cost circuit for providing protection for under-
voltage condition of power supply. As the project name suggest, its primary objective is protection of motors.
Although this circuit is completely operational to protect other kinds of equipment from under-voltage
condition. The other part, motor burnout protection requires several types of protection, like protection from
overloads, single phasing etc. As we are only concerned with protection of single phase motors, we are
providing overcurrent protection so that the motor would not burnout due to excessive heat. If either voltage
drops below a certain limit or the current exceeds a certain limit or both of these conditions occurs together,
the circuit trips and disconnects the motor from supply.
This circuit will operate in three cases- 1. Under-voltage, 2. Over-current, 3. Under-voltage and Over-current.
The Advantages of this circuit is- 1. High reliability, 2. Under voltage Protection, 3. Protect motors from
burning out, 4. High performance, 5. Low cost

6
CONTENTS
…………………………………………………………………………………………….........
o Chapter 1: Introduction & Overview……………………………………….....1
 1.1. Introduction……………………………………………………….....1-2
 1.2. Overview…………………………………………………………......3
o Chapter 2: Literature Review & Major Components.......................................4
 2.1. Literature Review................................................................................5-6
 2.2. Components Required……………………………………….............6-7
 2.3. Transformers…………………………………………………..........8-14
 2.4. Diode………………………………………………………….........15-19
 2.5. Capacitor……………………………………………………............20-24
 2.6. Resistor………………………………………………………..........25-28
 2.7. ICs…………………………………………………............................29
 2.7.1. Operational Amplifier (LM324)…………………….........29-34
 2.7.2. Voltage Regulator (IC7812 & IC7805)……………….......35-41
 2.7.3. AND Gate (IC7408)…………………………………........42-45
 2.7.4. NOT Gate (IC7404)………………………….....................46-48
 2.8. Potentiometer…………………………………………………..........49-53
 2.9. Transistor……………………………………………………............54-58
 2.10. Hall Effect Current Sensor (ACS712)……………………..............59-64
 2.11. Relay…………………………………………………...…..............65-69
o Chapter 3: Circuit Operation & Hardware Implementation………................70
 3.1. Block Diagram…………………………………………......................71
 3.2. Circuit Diagram & Circuit Operation …………………….......…....72-83
 3.3. Hardware Implementation…………………………….........................84

7
o Chapter 4: Results & Discussion………….......…………………........................85
 4.1. Results................................................................................................86-87
 4.1. Advantage……………………………………………..........................87
 4.2. Future Work…………………………………………........................87-88
 4.3. Conclusion………………………………………….............................88
References…………………………………………........................................................89-90
Publication...........................................................................................................................91
Appendix..........................................................................................................................92-94

8
LIST OF FIGURES
…………………………………………………………………………………………………..
Fig. No. 1: An ideal Transformer……………………………………………………………...9
Fig. No. 2: Ideal transformer as a circuit element……………………………………………..10
Fig. No. 3: Laminated core transformer..........................................................................….......12
Fig. No. 4: Lamination of the core…………………………………………………………...12
Fig. No. 5: Windings…………………………………………………………………………12
Fig. No. 6: A centre tap transformer…………………………………………………………14
Fig. No. 7: Full wave rectifier using centre tap transformer…………………………………14
Fig. No. 8: Electronic Symbol of Diode……………………………………………………..15
Fig. No. 9: p-n junction Diode……………………………………………………………….16
Fig. No. 10: Operation of Diode……………………………………………………………..16
Fig. No. 11: Zero Bias of Diode……………………………………………………………..17
Fig. No. 12: Forward Bias of Diode…………………………………………………………17
Fig. No. 13: Quasi-Fermi levels and carrier densities in forward biased p–n- diode………..18
Fig. No. 14: Reverse Bias of Diode………………………………………………………….18
Fig. No. 15: I–V (current vs. voltage) characteristics of a p–n junction diode………………19
Fig. No. 16: Electrolytic capacitor & Miniature low voltage capacitor……………………...20
Fig. No. 17: Charge separation in a parallel-plate capacitor…………………………………21
Fig. No. 18: Dielectric is placed between two conducting plates……………………………23
Fig. No. 19: Several capacitors in parallel…………………………………………………...24
Fig. No. 20: Several capacitors in series……………………………………………………..24

9
Fig. No. 21: A typical axial-lead resistor …………………………………………………....25
Fig. No. 22: Various resistors symbol.....................................................................................25
Fig. No. 23: IEC resistor symbol ………………………………………………………........25
Fig. No. 24: The hydraulic analogy of resistors…………………………………………......26
Fig. No. 25: Resistors in series ……………………………………………………………...27
Fig. No. 26: Resistors in parallel…………………………………………………………….27
Fig. No. 27: Circuit diagram symbol for an op-amp…………………………………………29
Fig. No. 28: An op-amp without negative feedback (a comparator)………….......…………30
Fig. No. 29: An equivalent circuit of an operational amplifier that models some resistive
Non-ideal parameters………………………………………………………......31
Fig. No. 30: Pin Diagram of IC LM324……………………………………………………..32
Fig. No. 31: Figure of IC7812……………………………………………………………….35
Fig. No. 32: Figure of IC7805……………………………………………………………….35
Fig. No. 33: Circuit design for a simple electromechanical voltage regulator……………....36
Fig. No. 34: Graph of voltage output on a time scale……………………..........................…37
Fig. No. 35: Pin Diagram of IC7812 & IC7805………………………………….………….37
Fig. No. 36: Symbols of AND Gate (IC7408)……………………………………………….42
Fig. No. 37: Pin Diagram of IC7408………………………………………………………...43
Fig. No. 38: Symbols of NOT Gate (IC7404)……………………………….………………46
Fig. No. 39: Pin Diagram of IC7404………………………………………...………………46
Fig. No. 40: A Typical Potentiometer………………………………………………………..49
Fig. No. 41: Electronic Symbol of Potentiometer………………………………….………...49

10
Fig. No. 42: Drawing of potentiometer with case cut away...............................….................50
Fig. No. 43: Single-turn potentiometer with metal casing removed to expose wiper
Contacts and resistive track………………………………………………….....51
Fig. No. 44: A potentiometer with a resistive load, showing equivalent fixed resistors
For clarity.............................................................................................................52
Fig. No. 45: Transistor CL100.................................................................................................54
Fig. No. 46: A simple circuit diagram to show the labels of an n–p–n bipolar transistor.......55
Fig. No. 47: A Bipolar NPN Transistor...................................................................................56
Fig. No. 48: NPN Transistor Connection..................................................................................57
Fig. No. 49: Input or driving characteristics.............................................................................58
Fig. No. 50: Output or collector characteristics.......................................................................58
Fig. No. 51: magnetic field......................................................................................................60
Fig. No. 52: Electromagnetism................................................................................................60
Fig. No. 53: Hall Effect measurement setup for electrons.......................................................61
Fig. No. 54: Automotive type miniature relay, dust cover is taken off...................................65
Fig. No. 55: Small "cradle" relay.............................................................................................66
Fig. No. 56: Circuit symbols of relays……………………………………………………….67
Fig. No. 57: A DPDT AC coil relay with "ice cube" packaging.............................................69
Fig. No. 58: Block Diagram of total circuit.............................................................................71
Fig. No. 59: The total circuit diagram of the under-voltage and overcurrent protection.........71
Fig. No. 60: Part-I of circuit diagram......................................................................................73
Fig. No. 61: Part-II of circuit diagram.....................................................................................74
Fig. No. 62: Part-III of circuit diagram....................................................................................75

11
Fig. No. 63: circuit diagram with current sensor.....................................................................76
Fig. No. 64: circuit diagram with current sensor and AND Gate............................................78
Fig. No. 65: Calibration of the resistance of trimpot for under-voltage protection.................80
Fig. No. 66: Circuit diagram with LM7812.............................................................................80
Fig. No. 67: Calibration of the resistance of trimpot for over current protection....................82
Fig. No. 68: Hardware circuit with Transformer.....................................................................84
Fig. No. 69: Hardware circuit without Transformer................................................................84
Fig. No. 70: Output Voltage to Relay Driver vs. Supply Voltage...........................................86
Fig. No. 71: Output Voltage Supplied To Load vs. Supply Voltage...................................................86
Fig. No. 72: Output Voltage to Relay Driver Circuit vs. Current Supplied To Load..........................87
LIST OF TABLES
……………………………………………………………………………………………..........
Table No. 1: Components Required………………………………………………………..6-7
Table No. 2: pin functions of LM324……………………………………………………… 33
Table No. 3: Electrical characteristics of LM324…………………………………………...34
Table No. 4: Electrical characteristics of LM7812……………………………………....38-39
Table No. 5: Electrical characteristics of LM7805…........................................................40-41
Table No. 6: Truth table of AND Gate…………………………………...…………………42
Table No. 7: Electrical characteristics of IC7408…………………………..……………43-44
Table No. 8: Switching Characteristics of IC7408……………………………………….....45
Table No. 9: Truth table of NOT Gate………………………………………………………46
Table No. 10: Electrical characteristics of IC7404………………………………………47-48

12
Table No. 11: Switching Characteristics of IC7404…………………………………………48
Table No. 12: Derating factors………………………………………………………………68
Table No. 13: Circuit Operation in brief………………………………………………….....79
List of Symbols, Abbreviations and Nomenclature
................................................................................................................................................
Transformer- Diode- Capacitor-
Vp = Primary Voltage, pB & nB = Bulk majority carrier C = Capacitance,
Vs = Secondary Voltage, densities on the p- Q = Charge,
Ip = Primary Current, -side and then-side, V = Voltage,
Is = Secondary Current, respectively. A = Plate area,
= Magnetic Flux, Vd = Drift Votage. d = Distance
Np = Primary Turns, between two
Ns = Secondary Turns, Plates.
a = Turns Ratio, W = Stored energy.
Transistor- Relay-
IE = Emitter Current NO = Normally Open,
IB = Base Current NC = Normally Closed,
IC = Collector Current CO = Change Over,
VBE = Voltage Base to Emitter SPST = Single Pole Single Throw,
VCE = Voltage Collector to Emitter SPDT = Single Pole Double Throw,
VCB = Voltage Collector to Base DPST = Double Pole Single Throw,
DPDT = Double Pole Double Throw.

13
Chapter: 01
Introduction & Overview

14
1.1.Introduction:
Motor Burnout- Electric motor windings are insulated with enamel. If for any reason somehow the motor
generates excessive heat, it will cause enamel insulation on the windings to break down and melt. Internal
shorts between the windings will then do the rest as the current will go up further and as a result, more heat
will be generated and the motor will smoke, smell bad and possibly eventually catch fire or just short out
blowing the fuse/breaker. This phenomenon is known as motor burnout.
Reasons for an electric motor to be burned out-
 Stalling the motor causing stall currents to flow.
 Overloading the motor with currents higher than the rating of the motor causing overheating the
windings, eddy current losses in the armature causing overheating and thermal runaway where
each breakdown causes more current to flow and more heat.
 Supplying too low a voltage causing operating current to go too high at rated HP load.
 Having inadequate supply wiring causing voltage loss at or near full HP load and current then
going too high in compensation causing winding overload and overheating.
 Blocking air vents or cooling fans.
Under-voltage- Under-voltage is defined as a condition where the applied voltage drops to 90% of rated
voltage, or less, for at least 1 minute. Low-voltage conditions occur when a machine asks for more power
than the line can deliver.
We can see that both the phenomenon of motor burnout and the under-voltage is associated with each
other. As the motor faces a problem of being supplied with lower voltage than rated, large current flows
through the motor, introducing an increased (I^2*R) loss, which in turn helps increasing the overall
heat. If this condition is tolerated for a long time, the insulation will breakdown, causing motor burnout.
Overcurrent- In an electric power system, overcurrent or excess current is a situation where a larger than
intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of
fire or damage to equipment. Possible causes for overcurrent include short circuits, excessive load, incorrect
design, or a ground fault. Fuses, circuit, temperature sensors and current limiters are commonly used
protection mechanisms to control the risks of overcurrent.

15
So, motor burnout and under-voltage protection is required for a steady and optimum operation of
a motor.
1.2.Overview:
This Under-voltage protection circuit is a reliable and low cost circuit for providing protection for
under-voltage condition of power supply. As the project name suggest, its primary objective is
protection of motors. Although this circuit is completely operational to protect other kinds of equipment
from under-voltage condition. The other part, motor burnout protection requires several types of
protection, like protection from overloads, single phasing etc. As we are only concerned with protection
of single phase motors, we are providing overcurrent protection so that the motor would not burnout
due to excessive heat. If either voltage drops below a certain limit or the current exceeds a certain limit
or both of these conditions occurs together, the circuit trips and disconnects the motor from supply.

16
Chapter: 02
Literature Review
&
Major Components

17
2.2.Literature Review:
Bayindir R. (2008) [6], discussed about fault detection and load protection with sensors which protects the devices
from under voltage and over voltage faults with the use of sensors. The sensors detects the faults and cut the supply
from the supply mains. According to the authors, the ability of protection system is demanded not only for economic
reason but for expert and reliable service.
Changchun Chi (2013) [7], discussed about research of the under voltage tripper with overvoltage protection function.
This paper designs a new under voltage tripper that has the function of overvoltage protection, to solve the problem
which the under voltage tripper coil can be burned down easily when the voltage fluctuates largely, causes the
operating region of the under voltage tripper with the high voltage dead areas, improves the reliability of circuit-
breaker and ensures the electric circuit normal operation.
Ponnle A. A, Omojoyegbe M. O. (2014) [8], presented a low cost under voltage and over current protection device
with a micro controller. The main purpose of the device is to isolate the load from over voltage and under voltage
conditions by controlling the relay tripping coil using a PIC micro controller. The microcontroller will compare the
supply voltage with the desired pre-set voltage and will operate the tripping coil in the relay if the input voltage falls
below or above the pre-set range of values. The design and the programming was simulated several times on Proteus
software until the code for the design worked satisfactorily before the final programming of the microcontroller and
assembly of the components. The type of programmer used for the microcontroller is a USB programmer, and the
programming code used is compiler CCS. The programming of the microcontroller was done by first writing the
program code in C#, after which it was compiled using the CCS compiler; then later the hex file was burned to the
PIC through the USB programmer. The device is well calibrated and manually tested. The preset was set at the voltage
200-240 volts. This device is found to be economical, easier to maintain and repair. The device cost about $50 to
produce.
Manish Paul (2014) [9], presented a paper on “Simulation of overvoltage and under voltage protection”. This paper
illustrates modelling and simulation of overvoltage and under voltage protection scheme. The method is based upon
the operation of relay under overvoltage and under voltage faults. The term power quality is used to describe as the
quality of power that is given as input to various electrical load and ability of load to function properly. Without proper
power the devices may mis-operate or fail. There are many ways in which electric power can be poor quality and many
more causes for such poor quality. Among the various power quality problems, overvoltage and under voltage are
frequent and severe. This paper demonstrates power quality, various causes and effects of overvoltage and under
voltage, and their protection. The test model of 230V, 50 Hz, has been designed in PSIM Demo Version 9.2.1.100.

18
Girish Chandra Thakur (2015) [10], presented a research paper on “Implementation of Single Phasing, Over
Voltage, Under Voltage, and Protection of Three Phase Appliances without Using Microcontroller”. This paper tends
to develop for protection for costly appliances which require three-phase AC supply for operation. Failure of any of
the phases or sudden change in voltage makes the appliance prone to erratic functioning and may even lead to failure.
Hence it is of paramount importance to monitor the availability of the three-phase supply and proper voltage supply
and switch off the appliance in the event of failure of one or two phases or if required voltage level is not available.
The power to the appliance should resume with the availability of all phases of the supply with proper voltage level.
The main advantage of this protector circuit is that it protects three-phase appliances from failure of any phase as well
as from fluctuation of voltage. The concept in future can be extended to developing a mechanism to send message to
the authority via SMS by interfacing GSM modem.
2.2. Components Required:
Name of the components Specifications Quantity
1.Resistors (a) 10k
(b) 5.6k
(c) 1ohm/1W
(d) 27k/0.25W
(e) 2.2k
(d) 3.3k
1
1
1
1
1
1
2.Capacitors (a) 47uF/63V
(b)10uF/63V
(c)1uF/63V
1
1
1
3.ICs (a) LM324
(b) LM7812
(c) LM7805
1
1
1

19
(d) IC7808
(e) IC7404
1
1
4.Diodes IN4007 , 1000V 7
5.Transistor CL100 , NPN 1
6.Potentiometer(Trimpot) 22k 1
7.Transformer 230V/9-CT-9 V , 500mA 1
8.Relay 12V, 1CO, 5A 2
9.Connecting Wires N/A As per required
10.Bread Board N/A 2
11. LED N/A 1
12. Current Sensor 5 A 1
Table No. 1

20
2.3. Transformer:
A transformer is an electrical device that transfers electrical energy between two or more circuits
through electromagnetic induction. Electromagnetic induction produces an electromotive force within a
conductor which is exposed to time varying magnetic fields. Transformers are used to increase or decrease
the alternating voltages in electric power applications.
A varying current in the transformer's primary winding creates a varying magnetic flux in the transformer
core and a varying field impinging on the transformer's secondary winding. This varying magnetic field at
the secondary winding induces a varying electromotive force (EMF) or voltage in the secondary winding
due to electromagnetic induction.
Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone
to huge units weighing hundreds of tons used in power stations or to interconnect portions of power grids.
All operates on the same principles, although the range of designs is wide. While new technologies have
eliminated the need of transformers in some electronics circuits, transformer are still found in nearly all
electronics devices designed for household (“mains”) voltage. Transformers are essential for high voltage
electric power transmission, which, makes long-distance transmission economically practical.
 Basic Principles-
The transformer is based on two principles: first, that an electric current can produce a magnetic field
(electromagnetism) and second that changing magnetic field within a coil of wire induces a voltage across
the ends of the coil (electromagnetic coil). Changing the current in the primary coil changes the magnetic
flux is developed. The changing magnetic flux induces in the secondary coil.
An ideal transformer is shown in the figure below. Current passing the primary coil creates a magnetic field.
The primary and secondary coils are wrapped a core o very high magnetic permeability, such as iron so that
most of the magnetic flux passes through both the primary and secondary coils. If a load is connected to the
secondary winding the load current and voltage will be in the directions indicated, given the primary current
and voltage in the directions indicated (each will be alternating current in practice).

21
 Induction Law-
Fig No. -1
An ideal Transformer
An ideal voltage step down transformer. The secondary current arises from the secondary EMF on the (not
shown) load impedance.
The voltage induced across secondary coil may be calculated from Faraday’s law of induction, which states
that:
Where Vs is the instantaneous voltage, Ns is the number of turns in the secondary coil and is the magnetic
flux through one turn of coil. If the turns of coil are oriented perpendicularly to the magnetic field lines, the
flux is the product of the magnetic flux density B and the area A throgh which it cuts. The area is constant
,being equal to the cross sectional area of the transformer core. Whreas the magnetic field varies with time
according to the excitation of the primary. Since the same magnetic flux passes through both the primary
and secondary coils in an ideal transformer.
The instantaneous voltage across the primary winding equals,

22
Taking the ratio of the two equations for Vs and Vp gives the basic equation for stepping up and stepping
down the volatge ,
Np/Ns is equal to the turn’s ratio and is the primary functional characteristic of any transformer. In the case
of step up, thus may sometimes be stated as the reciprocal Ns/Np. Turns ratio is commonly expressed as an
irreducible function or ratio, for example, a transformer with primary and secondary windings of respectively
100 and 150 turns is said to have e turns ratio of 2:3 rather than 0.667 or 100:150.
 Ideal Power Equation-
The ideal transformer as a circuit element
Fig. No. - 2
If load is connected to the secondary winding, current will flow in this winding and electrical energy will be
transferred from the primary circuit through the transformer to the load. Transformers may be used for AC-
to-AC conversion of a single power frequency or for conversion of single power over a wide range
frequencies such as audio or radio frequencies.

23
In an ideal transformer, the induced voltage in the secondary winding (Vs) is in opposition to the primary
voltage (Vp) is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the
primary (Np) as follows.
By appropriate selection of the ratio of turns, a transformer thus enables an alternating current (AC) voltage
to be “stepped up” by making Ns greater than Np, or “stepped down” by making Ns less than Np. The
windings are coils wound around a ferromagnetic core, air-crossed transformer being a notable exception.
If the secondary coil is attached to the load that allows to flow, electrical power is transmitted from the
primary circuit to secondary circuit ideally, the transformer is perfectly efficient. All the incoming energy is
transformed from primary circuit to the magnetic field and into the secondary circuit. If this condition is met,
the input electric power must equal to input power:
Giving the ideal transformer equation,
This formula is a reasonable approximation for commercial transformers.
If the voltage is increased, then the current is decreased by the same factor. The impedance in one circuit is
transformed by the square of the turns ratio. For example, if an impedance Zs is attached across the terminals
of the secondary coil, it appears to the primary circuit to have an impedance if (Np/Ns) 2Zs. This relationship
is reciprocal , so that the impedance Zp of the primary circuit appears to the secondary to be (Ns/Np)2Zp.

24
 Cores-
Laminated steel cores
Fig No. – 3
Laminated core transformer showing edge of laminations at top of photo
Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel. The
steel has a permeability many times that of free space and the core thus serves to greatly reduce the magnetizing current
and confine the flux to a path which closely couples the windings. Early transformer developers soon realized that
cores constructed from solid iron resulted in prohibitive eddy current losses, and their designs mitigated this effect
with cores consisting of bundles of insulated iron wires. Later designs constructed the core by stacking layers of thin
steel laminations, a principle that has remained in use. Each lamination is insulated from its neighbours by a thin non-
conducting layer of insulation. The universal transformer equation indicates a minimum cross-sectional area for the
core to avoid saturation.
The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so
reduce their magnitude. Thinner laminations reduce losses, but are more laborious and expensive to
construct. Thin laminations are generally used on high-frequency transformers, with some of very thin steel
laminations able to operate up to 10 kHz.
Fig No. – 4
Laminating the core greatly reduces eddy-current losses

25
 Windings-
Fig. No. – 5
Windings are usually arranged concentrically to minimize flux leakage
The conducting material used for the windings depends upon the application, but in all cases the individual
turns must be electrically insulated from each other to ensure that the current travels throughout every turn.
For small power and signal transformers, in which currents are low and the potential difference between
adjacent turns is small, the coils are often wound from enamelled magnet wire, such as Formvar wire. Larger
power transformers operating at high voltages may be wound with copper rectangular strip conductors
insulated by oil-impregnated paper and blocks of pressboard.
 Centre taps Transformers-
In electronics, a centre tap (CT) is a contact made to a point halfway along a winding of a transformer or
inductor, or along the element of a resistor or a potentiometer. Taps are sometimes used on inductors for the
coupling of signals, and may not necessarily be at the half-way point, but rather, closer to one end. A common
application of this is in the Hartley oscillator. Inductors with taps also permit the transformation of the
amplitude of alternating current (AC) voltages for the purpose of power conversion, in which case, they are
referred to as autotransformers, since there is only one winding. An example of an autotransformer is an
automobile ignition coil. Potentiometer tapping provides one or more connections along the device's element,
along with the usual connections at each of the two ends of the element, and the slider connection.
Potentiometer taps allow for circuit functions that would otherwise not be available with the usual
construction of just the two end connections and one slider connection.

26
Fig. No. – 6 Fig No. - 7
A centre tap transformer
 Bushings-
Larger transformers are provided with high-voltage insulated bushings made of polymers or porcelain. A
large bushing can be a complex structure since it must provide careful control of the electric field
gradient without letting the transformer leak oil.

27
2.4. Diode:
In electronics, a diode is a two-terminal electronic component that conducts primarily in one direction
(asymmetric conductance); it has low (ideally zero) resistance to the flow of current in one direction, and
high (ideally infinite) resistance in the other. A semiconductor diode, the most common type today, is a
crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals. A
vacuum tube diode has two electrodes, a plate (anode) and a heated cathode. Semiconductor diodes were the
first semiconductor electronic devices. The discovery of crystals' rectifying abilities was made by German
physicist Ferdinand Braun in 1874. The first semiconductor diodes, called cat's whisker diodes, developed
around 1906, were made of mineral crystals such as galena. Today, most diodes are made of silicon, but
other semiconductors such as selenium or germanium are sometimes used.
Fig. No. – 8
Electronic Symbol
The most common function of a diode is to allow an electric current to pass in one direction (called the
diode's forward direction), while blocking current in the opposite direction (the reverse direction). Thus, the
diode can be viewed as an electronic version of a check valve. This unidirectional behaviour is called
rectification, and is used to convert alternating current to direct current, including extraction of modulation
from radio signals in radio receivers—these diodes are forms of rectifiers.
 P-N Junction Diode-
A p–n junction diode is made of a crystal of semiconductor, usually silicon, but germanium and gallium
arsenide are also used. Impurities are added to it to create a region on one side that contains negative charge
carriers (electrons), called an n-type semiconductor, and a region on the other side that contains positive
charge carriers (holes), called a p-type semiconductor. When the two materials i.e. n-type and p-type are
attached together, a momentary flow of electrons occur from the n to the p side resulting in a third region
between the two where no charge carriers are present. This region is called the depletion region due to the

28
absence of charge carriers (electrons and holes in this case). The diode's terminals are attached to the n-type
and p-type regions. The boundary between these two regions, called a p–n junction, is where the action of
the diode takes place. When a higher electrical potential is applied to the P side (the anode) than to the N
side (the cathode), it allows electrons to flow from the N-type side to the P-type side. The junction does not
allow the flow of electrons in the opposite direction when the potential is applied in reverse, creating, in a
sense, an electrical check valve.
Fig. No. – 9
 Operation-
Here, the operation of the abrupt p–n diode is considered. By "abrupt" is meant that the p- and n-type doping
exhibit a function discontinuity at the plane where they encounter each other. The objective is to explain the
various bias regimes in the figure displaying current-voltage characteristics. Operation is described
using band-bending diagrams that show how the lowest conduction band energy and the highest valence
band energy vary with position inside the diode under various bias conditions. For additional discussion, see
the articles Semiconductor and Band diagram
Fig. No. – 10

29
 Zero bias-
The figure shows a band bending diagram for a p–n diode; that is, the band edges for the conduction band
(upper line) and the valence band (lower line) are shown as a function of position on both sides of the junction
between the p-type material (left side) and the n-type material (right side). When a p-type and an n-type
region of the same semiconductor are brought together and the two diode contacts are short-circuited,
the Fermi half-occupancy level (dashed horizontal straight line) is situated at a constant level. This level
ensures that in the field-free bulk on both sides of the junction the hole and electron occupancies are correct.
(So, for example, it is not necessary for an electron to leave the n-side and travel to the p-side through the
short circuit to adjust the occupancies.)
Fig. No. – 11
Band-bending diagram for p–n diode at zero applied voltage. The depletion region is shaded
 Forward bias-
In forward bias, positive terminal of the battery is connected to the p- type material and negative terminal is
connected to the n- type material so that holes are injected into the p-type material and electrons into the n-
type material. The electrons in the n-type material are called majority carriers on that side, but electrons that
make it to the p-type
Fig. No. - 12

30
side are called minority carriers. The same descriptors apply to holes: they are majority carriers on the p-
type side, and minority carriers on the n-type side.
Fig. No. – 13
Quasi-Fermi levels and carrier densities in forward biased p–n diode. The figure assumes recombination is
confined to the regions where majority carrier concentration is near the bulk values, which is not accurate
when recombination-generation centres in the field region play a role.
 Reverse bias-
In reverse bias the occupancy level for holes again tends to stay at the level of the bulk p-type semiconductor
while the occupancy level for electrons follows that for the bulk n-type. In this case, the p-type bulk band
edges are raised relative to the n-type bulk by the reverse bias vR, so the two bulk occupancy levels are
separated again by an energy determined by the applied voltage
Fig. No. – 14
As shown in the diagram, this behaviour means the step in band edges is increased to φB+vR, and the
depletion region widens as holes are pulled away from it on the p-side and electrons on the n-side.

31
 Current–voltage characteristic-
A semiconductor diode's behaviour in a circuit is given by its current–voltage characteristic, or I–V graph
(see graph below). The shape of the curve is determined by the transport of charge carriers through the so-
called depletion or depletion region that exists at the p–n junction between differing semiconductors. When
a p–n junction is first created, conduction-band (mobile) electrons from the N-doped region diffuse into the
P-doped region where there is a large population of holes (vacant places for electrons) with which the
electrons "recombine". When a mobile electron recombines with a hole, both hole and electron vanish,
leaving behind an immobile positively charged donor (dopant) on the N side and negatively charged acceptor
(dopant) on the P side. The region around the p–n junction becomes depleted of carriers and thus behaves as
an insulator.
Fig, No. – 15
I–V (current vs. voltage) characteristics of a p–n junction diode

32
2.5. Capacitor:
A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store
electrical energy temporarily in an electric field. The forms of practical capacitors vary widely, but all contain
at least two electrical conductors (plates) separated by a dielectric (i.e. an insulator that can store energy by
becoming polarized). The no conducting dielectric acts to increase the capacitor's charge capacity. Materials
commonly used as dielectrics include glass, ceramic, plastic film, air, vacuum, paper, mica, and oxide layers.
Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike
a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of
an electrostatic field between its plates.
When there is a potential difference across the conductors (e.g., when a capacitor is attached across a battery),
an field develops across the dielectric, causing positive charge +Q to collect on one plate and negative charge
−Q to collect on the other plate. If a battery has been attached to a capacitor for a sufficient amount of time,
no current can flow through the capacitor. However, if a time-varying voltage is applied across the leads of
the capacitor, a displacement current can flow.
The larger the surface area of the "plates" (conductors) and the narrower the gap between them, the greater
the capacitance is. In practice, the dielectric between the plates passes a small amount of leakage current and
also has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce
an undesired inductance and resistance.
4 Electrolytic capacitor with different Miniature low voltage capacitors
voltages and capacitance (next to a cm ruler)
Fig. No. – 16

33
 Theory of operation-
A capacitor consists of two conductors separated by a non-conductive region. The non-conductive region is
called the dielectric. In simpler terms, the dielectric is just an electrical insulator. Examples of dielectric
media are glass, air, paper, vacuum, and even a semiconductor depletion chemically identical to the conductors.
The conductors thus hold equal and opposite charges on their facing surfaces, and the dielectric develops an
electric field. In SI units, a capacitance of one farad means that one coulomb of charge on each conductor
causes a voltage of one volt across the device.
An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of charge ±Q on
each conductor to the voltage V between them:
Because the conductors (or plates) are close together, the opposite charges on the conductors attract one
another due to their electric fields, allowing the capacitor to store more charge for a given voltage than if the
conductors were separated, giving the capacitor a large capacitance.
Sometimes charge build up affects the capacitor mechanically, causing it capacitance to vary. In this case,
capacitance is defined in terms of incremental charges:
Fig. No. – 17
Charge separation in a parallel-plate capacitor causes an internal electric field. A dielectric (orange) reduces the
field and increases the capacitance.

34
 Energy of electric field-
Work must be done by an external influence to "move" charge between the conductors in a capacitor. When
the external influence is removed, the charge separation persists in the electric field and energy is stored to
be released when the charge is allowed to return to its equilibrium position. The work done in establishing
the electric field, and hence the amount of energy stored, is
Here Q is the charge stored in the capacitor, V is the voltage across the capacitor, and C is the capacitance.
In the case of a fluctuating voltage V (t), the stored energy also fluctuates and hence power must flow into
or out of the capacitor. This power can be found by taking the time derivative of the stored energy:
 Current–voltage relation-
The current I (t) through any component in an electric circuit is defined as the rate of flow of a charge Q (t)
passing through it, but actual charges—electrons—cannot pass through the dielectric layer of a capacitor.
Rather, one electron accumulates on the negative plate for each one that leaves the positive plate, resulting
in an electron depletion and consequent positive charge on one electrode that is equal and opposite to the
accumulated negative charge on the other. Thus the charge on the electrodes is equal to the integral of the
current as well as proportional to the voltage, as discussed above. As with any ant derivative, a constant of
integration is added to represent the initial voltage (t0). This is the integral form of the capacitor equation:
Taking the derivative of this and multiplying by C yields the derivative form:

35
 Parallel-plate model-
The simplest model capacitor consists of two thin parallel conductive plates separated by a dielectric
with permittivity ε. This model may also be used to make qualitative predictions for other device geometries.
The plates are considered to extend uniformly over an area A and a charge density ±ρ = ±Q/A exists on their
surface. Assuming that the length and width of the plates are much greater than their separation d, the electric
field near the center of the device will be uniform with the magnitude E = ρ/ε. The voltage is defined as
the line integral of the electric field between the plates
Fig. No. – 18
Dielectric is placed between two conducting plates, each of area A and with a separation of d
Solving this for C = Q/V reveals that capacitance increases with area of the plates, and decreases as separation
between plates increases.
The capacitance is therefore greatest in devices made from materials with a high permittivity, large
plate area, and small distance between plates.

36
 Networks-
For capacitors in parallel
Capacitors in a parallel configuration each have the same applied voltage. Their capacitances add up. Charge
is apportioned among them by size. Using the schematic diagram to visualize parallel plates, it is apparent
that each capacitor contributes to the total surface area.
Fig. No. 19
Several capacitors in parallel
For capacitors in series
Connected in series, the schematic diagram reveals that the separation distance, not the plate area, adds up.
The capacitors each store instantaneous charge build-up equal to that of every other capacitor in the series.
The total voltage difference from end to end is apportioned to each capacitor according to the inverse of its
capacitance. The entire series acts as a capacitor smaller than any of its components.
Fig. No. - 20
Several capacitors in series

37
2.6. Resistors:
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit
element. Resistors act to reduce current flow, and, at the same time, act to lower voltage levels within circuits.
In electronic circuits, resistors are used to limit current flow, to adjust signal levels, bias active elements, and
terminate transmission lines among other uses. High-power resistors, that can dissipate many watts of
electrical power as heat, may be used as part of motor controls, in power distribution systems, or as test loads
for generators. Fixed resistors have resistances that only change slightly with temperature, time or operating
voltage. Variable resistors can be used to adjust circuit elements (such as a volume control or a lamp
dimmer), or as sensing devices for heat, light, humidity, force, or chemical activity.
Fig. No. – 21
A typical axial-lead resistor
Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic
equipment. Practical resistors as discrete components can be composed of various compounds and forms.
Resistors are also implemented within integrated circuits.
The electrical function of a resistor is specified by its resistance: common commercial resistors are
manufactured over a range of more than nine orders of magnitude.
 Electronic symbols and notation-
Two typical schematic diagram symbols are as follows:
Fig. No. - 22 Fig. No. - 23
(a) resistor, (b) rheostat (variable resistor), IEC resistor symbol
And (c) potentiometer

38
 Theory of operation-
The behaviour of an ideal resistor is dictated by the relationship specified by Ohm's law:
V= I . R
Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the constant
of proportionality is the resistance (R). For example, if a 300 ohm resistor is attached across the terminals of
a 12 volt battery, then a current of 12 / 300 = 0.04 amperes flows through that resistor.
Practical resistors also have some inductance and capacitance which will also affect the relation between
voltage and current in alternating current circuits.
The ohm (symbol: Ω) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is
equivalent to a volt per ampere. Since resistors are specified and manufactured over a very large range of
values, the derived units of milliohm (1 mΩ = 10−3 Ω), kilohm (1 kΩ = 103 Ω), and megohm (1 MΩ = 106
Ω) are also in common usage.
Fig. No. – 24
The hydraulic analogy compares electric current flowing through circuits to water flowing through pipes.
When a pipe (left) is filled with hair (right), it takes a larger pressure to achieve the same flow of water.
Pushing electric current through a large resistance is like pushing water through a pipe clogged with hair: It
requires a larger push (voltage drop) to drive the same flow (electric current).

39
 Series and parallel resistors-
The total resistance of resistors connected in series is the sum of their individual resistance values.
Fig. No. - 25
The total resistance of resistors connected in parallel is the reciprocal of the sum of the reciprocals of the
individual resistors.
Fig. No. - 26
So, for example, a 10 ohm resistor connected in parallel with a 5 ohm resistor and a 15 ohm resistor will
produce the inverse of 1/10+1/5+1/15 ohms of resistance, or 1/(.1+.2+.067)=2.725 ohms.
A resistor network that is a combination of parallel and series connections can be broken up into smaller
parts that are either one or the other. Some complex networks of resistors cannot be resolved in this manner,
requiring more sophisticated circuit analysis. Generally, the Y-Δ transform, or matrix methods can be used
to solve such problems.

40
 Power dissipation-
At any instant, the power P (watts) consumed by a resistor of resistance R (ohms) is calculated
as: where V (volts) is the voltage across the resistor and I (amps) is the current flowing through it.
Using Ohm's law, the two other forms can be derived. This power is converted into heat which must be dissipated by the
resistor's package before its temperature rises excessively.
Resistors are rated according to their maximum power dissipation. Discrete resistors in solid-state electronic systems are
typically rated as 1/10, 1/8, or 1/4 watt. They usually absorb much less than a watt of electrical power and require little
attention to their power rating.
 Resistor marking-
Most axial resistors use a pattern of coloured stripes to indicate resistance, which also indicate tolerance, and
may also be extended to show temperature coefficient and reliability class. Cases are usually tan, brown,
blue, or green, though other colours are occasionally found such as dark red or dark grey. The power rating
is not usually marked and is deduced from the size.
The colour bands of the carbon resistors can be three, four, five or, six bands. The first two bands represent
first two digits to measure their value in ohms. The third band of a three- or four-banded resistor represents
multiplier; a fourth band denotes tolerance (which if absent, denotes ±20%). For five and six colour-banded
resistors, the third band is a third digit, fourth band multiplier and fifth is tolerance. The sixth band represents
temperature co-efficient in a six-banded resistor.

41
2.7. ICs:
2.7.1.Operational amplifier (LM324):
An operational amplifier (often op-amp or opamp) is a DC-coupled high-gain electronic voltage amplifier
with a differential input and, usually, a single-ended output.[1] In this configuration, an op-amp produces an
output potential (relative to circuit ground) that is typically hundreds of thousands of times larger than the
potential difference between its input terminals. Operational amplifiers had their origins in analog computers,
where they were used to do mathematical operations in many linear, non-linear and frequency-dependent
circuits. The popularity of the op-amp as a building block in analog circuits is due to its versatility. Due to
negative feedback, the characteristics of an op-amp circuit, its gain, input and output impedance, bandwidth
etc. are determined by external components and have little dependence on temperature coefficients or
manufacturing variations in the op-amp itself.
 Electronic symbol-
Fig. No. – 27
Circuit diagram symbol for an op-amp
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 labelled in different ways (See IC power supply

42
pins). Often these pins are left out of the diagram for clarity, and the power configuration is described or
assumed from the circuit.
 Operation-
The amplifier's differential inputs consist of a non-inverting input (+) with voltage V+ and an inverting input
(–) with voltage V−; 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 Vout is given by the equation:
Where 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).
Open loop amplifier-
The magnitude of AOL is typically very large—100,000 or more for integrated circuit op-amps—and
therefore even a quite small difference between V+ and V− drives the amplifier output nearly to the supply
voltage. Situations in which the output voltage is equal to or greater than the supply voltage are referred to
as saturation of the amplifier. The magnitude of AOL is not well controlled by the manufacturing process,
and so it is impractical to use an open loop amplifier as a stand-alone differential amplifier.
Fig. No. – 28
An op-amp without negative feedback (a comparator)
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 Rg, and the input voltage
Vin applied to the non-inverting input is positive, the output will be maximum positive; if Vin is negative,

43
the output will be maximum negative. Since there is no feedback from the output to either input, this is an
open loop circuit acting as a comparator.
Closed loop amplifier-
If predictable operation is desired, negative feedback is used, by applying a portion of the output voltage to
the inverting input. The closed loop feedback greatly reduces the gain of the circuit. When negative feedback
is used, the circuit's overall gain and response becomes determined mostly by the feedback network, rather
than by the op-amp characteristics. If the feedback network is made of components with values small relative
to the op amp's input impedance, the value of the op-amp's open loop response AOL does not seriously affect
the circuit's performance. The response of the op-amp circuit with its input, output, and feedback circuits to
an input is characterized mathematically by a transfer function; designing an op-amp circuit to have a desired
transfer function is in the realm of electrical engineering. The transfer functions are important in most
applications of op-amps, such as in analog computers. High input impedance at the input terminals and low
output impedance at the output terminal(s) are particularly useful features of an op-amp.
In the non-inverting amplifier on the right, the presence of negative feedback via the voltage divider Rf, Rg
determines the closed-loop gain ACL = Vout / Vin. 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 thus 1 + Rf/Rg. As a simple example, if Vin = 1 V and Rf = Rg, Vout will be 2 V, exactly
the amount required to keep V− at 1 V. Because of the feedback provided by the Rf, Rg network, this is a
closed loop circuit.
Fig. No. – 29
An equivalent circuit of an operational amplifier that models some resistive non-ideal parameters.

44
Another way to analyse this circuit proceeds by making the following (usually valid) assumptions:
When an op-amp operates in linear (i.e., not saturated) mode, the difference in voltage between the non-
inverting (+) pin and the inverting (−) pin is negligibly small.
The input impedance between (+) and (−) pins is much larger than other resistances in the circuit.
The input signal Vin appears at both (+) and (−) pins, resulting in a current i through Rg equal to Vin/Rg.
since Kirchhoff's current law states that the same current must leave a node as enter it, and since the
impedance into the (−) pin is near infinity, we can assume practically all of the same current i flows through
Rf, creating an output voltage
By combining terms, we determine the closed-loop gain ACL:
 Pin Diagram of IC LM324-
Fig. No. - 30

45
 Pin Functions-
PIN
TYPE DESCRIPTI
ONNAME NO
.OUTPUT1 1 O Output, Channel 1
INPUT1- 2 I Inverting Input, Channel 1
INPUT1+ 3 I Non inverting Input, Channel 1
V+ 4 P Positive Supply Voltage
OUTPUT2 7 O Output, Channel 2
GND 11 P Ground or Negative Supply Voltage
Table No. - 2
 The specifications of LM324-
1. The power supply voltage range that they use: +3 volts to +30 volts.
2. The power supply current (minimum) that they use: 0.8 mili amperes.
3. The normal output current each op-amp (at pin-output to ground) of: 20 mili amperes typical (10 ma
minimum).
4. The output current that flow from the positive supply to output-pin): 8 mill amperes typical (5 mA
minimum).
5. The maximum voltage gain (typical): 100,000. The gain is set by a feedback resistors between output-
pin and inverting (-) input.
 The application of LM324-
The LM324 has numerous circuit application. We can use it in many projects.

46
PARAMETER TEST CONDITIONS
LM324A
UNIT
MIN TYP MAX
Input Offset Voltage TA = 25°C(2) 2 3 mV
Input Bias Current(3)
IIN(+) or IIN(−), VCM = 0 V,
TA = 25°C 45 100 nA
Input Offset Current
IIN(+) or IIN(−), VCM = 0 V,
TA = 25°C 5 30 nA
Input Common-Mode
Voltage Range(4)
V+ = 30 V, (LM2902-N, V+
= 26 V), TA = 25°C V+ -
1.5
V
Supply Current
Over Full Temperature Range,
RL = ∞ On All Op Amps
V+ = 30 V (LM2902-N V+ =
26V)
1.5 3
mA
V+ = 5 V 0.7 1.2
Large Signal
Voltage Gain
V+ = 15 V, RL≥ 2 kΩ,
(VO = 1 V to 11 V), TA = 25°C
25 100 V/mV
Common-Mode
Rejection Ratio
DC, VCM = 0 V to V+ − 1.5 V,
TA = 25°C 65 85 dB
Power Supply
Rejection Ratio
V+ = 5 V to 30 V, (LM2902-N,
V+ = 5V to 26 V),
TA = 25°C
65 100 dB
Amplifier-to-Amplifier
Coupling(5)
f = 1 kHz to 20 kHz, TA = 25°C,
(Input Referred)
−120 dB
Output
Current
Source
V+ = 1 V, V − = 0 V,
V+ = 15 V, VO = 2 V, TA = 25°C
20 40 mA
Sink
V− = 1 V, V + = 0 V,
V+ = 15 V, VO = 2 V, TA = 25°C
10 20
μA
VIN− = 1 V, V + = 0 V,
V+ = 15 V, VO = 200 mV, TA =
25°C
12 50
Short Circuit to Ground
V+ = 15V
TA = 25°C(6)
40 60 mA
Input Offset Voltage See(2) 5 mV
VOS Drift RS = 0 Ω 7 30 μV/°C
Input Offset Current IIN(+) − IIN(−), VCM = 0 V 75 nA
 Electrical Characteristics (Table No.-3) -

47
2.7.2. Voltage regulator (LM7412 & LM7805):
A voltage regulator is designed to automatically maintain a constant voltage level. A voltage
regulator may be a simple "feed-forward" design or may include negative feedback control
loops. It may use an electromechanical mechanism, or electronic components. Depending on
the design, it may be used to regulate one or more AC or DC voltages.
Electronic voltage regulators are found in devices such as computer power supplies where they
stabilize the DC voltages used by the processor and other elements. In automobile alternators
and central power station generator plants, voltage regulators control the output of the plant. In
an electric power distribution system, voltage regulators may be installed at a substation or
along distribution lines so that all customers receive steady voltage independent of how much
power is drawn from the line.
Fig. No. – 31 Fig. No.- 32
An integrated circuit voltage regulator in a TO-220 style package. Such devices are popular
because they require few or no external components and provide the functions of pass element,
voltage reference, and protection from overcurrent in one package.
 Electronic voltage regulators-
A simple voltage regulator can be made from a resistor in series with a diode (or series of
diodes). Due to the logarithmic shape of diode V-I curves, the voltage across the diode changes
only slightly due to changes in current drawn or changes in the input. When precise voltage
control and efficiency are not important, this design may work fine.
Feedback voltage regulators operate by comparing the actual output voltage to some fixed
reference voltage. Any difference is amplified and used to control the regulation element in
such a way as to reduce the voltage error. This forms a negative feedback control loop;

48
increasing the open-loop gain tends to increase regulation accuracy but reduce stability.
(Stability is avoidance of oscillation, or ringing, during step changes.) There will also be a
trade-off between stability and the speed of the response to changes. If the output voltage is too
low (perhaps due to input voltage reducing or load current increasing), the regulation element
is commanded, up to a point, to produce a higher output voltage–by dropping less of the input
voltage (for linear series regulators and buck switching regulators), or to draw input current for
longer periods (boost-type switching regulators); if the output voltage is too high, the regulation
element will normally be commanded to produce a lower voltage. However, many regulators
have over-current protection, so that they will entirely stop sourcing current (or limit the current
in some way) if the output current is too high, and some regulators may also shut down if the
input voltage is outside a given range.
 Electromechanical regulators-
An electromechanical regulators, voltage regulation is easily accomplished by coiling the
sensing wire to make an electromagnet. The magnetic field produced by the current attracts a
moving ferrous core held back under spring tension or gravitational pull. As voltage increases,
so does the current, strengthening the magnetic field produced by the coil and pulling the core
towards the field. The magnet is physically connected to a mechanical power switch, which
opens as the magnet moves into the field. As voltage decreases, so does the current, releasing
spring tension or the weight of the core and causing it to retract. This closes the switch and
allows the power to flow once more.
Fig. No. – 33
Circuit design for a simple electromechanical voltage regulator

49
If the mechanical regulator design is sensitive to small voltage fluctuations, the motion of the
solenoid core can be used to move a selector switch across a range of resistances or transformer
windings to gradually step the output voltage up or down, or to rotate the position of a moving-
coil AC regulator.
 Automatic voltage regulator-
To control the output of generators (as seen in ships and power stations, or on oil rigs,
greenhouses and emergency power systems) automatic voltage regulators are used. This is an
active system. While the basic principle is the same, the system itself is more complex. An
automatic voltage regulator (or AVR for short) consists of several components such as diodes,
capacitors, resistors and potentiometers or even microcontrollers, all placed on a circuit board.
This is then mounted near the generator and connected with several wires to measure and adjust
the generator.
How an AVR works: In the first place the AVR
monitors the output voltage and controls the
input voltage for the exciter of the generator.
By increasing or decreasing the generator
control voltage, the output voltage of the
generator increases or decreases accordingly.
The AVR calculates how much voltage has to Fig. No. – 34
be sent to the exciter numerous times a second, Graph of voltage output on a time scale
therefore stabilizing the output voltage to a predetermined set point. When two or more
generators are powering the same system (parallel operation) the AVR receives information
from more generators to match all output.
 Pin Diagram of LM7812 & LM7805–
Fig. No. - 35

50
 Electrical Characteristics of LM7812–
Output Voltage 5V
Input Voltage (unless otherwise noted) 10V Units
Symbol Parameter Conditions Min Typ Max
VO Output Voltage Tj = 25ÊC, 5 mA  IO  1A 11.5 12 12.5 V
PD  15W, 5 mA  IO  1A 11.4 12.6 V
V
MIN  V
IN  V
MAX (14.5  VIN  V
VO Line Regulation IO = 500 Tj = 25ÊC 4 120 mV
mA
VIN 14.5  VIN  30) V
0ÊC  Tj  +125ÊC 120 mV
VIN (15  VIN  27) V
IO 1A Tj = 25ÊC 120 mV
V
IN (14.6  VIN  V
27)
0ÊC  Tj  +125ÊC 60 mV
VIN
(16 VIN  22) V
VO Load Regulation Tj = 25ÊC 5 mA  IO  1.5A 12 120 mV
250 mA  IO  60 mV
750 mA
5 mA  IO  1A, 0ÊC  Tj  120 mV
+125ÊC
I
Q Quiescent Current IO  1A Tj = 25ÊC 8 mA
0ÊC  Tj  +125ÊC 8.5 mA
IQ Quiescent Current 5 mA  IO  1A 0.5 mA
Change Tj = 25ÊC, IO 1A 1.0 mA
V
MIN  V
IN  V
MAX (14.8  VIN 27) V
IO  500 mA, 0ÊC  Tj  +125ÊC 1.0 mA
V
MIN  V
IN  V
MAX (14.5  VIN 30) V

51
Output Voltage 5V
V
N Output Noise TA =25ÊC, 10 Hz  f  100 kHz 75 µV
Voltage
Ripple Rejection IO  1A, Tj = 25ÊC 55 72 dB
Or
f = 120 Hz IO  500 mA 55 dB
0ÊC Tj  +125ÊC
V
MIN  V
IN  V
MAX (15  VIN  25) V
RO Dropout Voltage Tj = 25ÊC, IOUT = 1A 2.0 V
Output Resistance f = 1 kHz 18 m
Short-Circuit
Current
Peak Output
Current
Average TC of
VOUT
Tj = 25ÊC
Tj = 25ÊC
0ÊC  Tj  +125ÊC, Io = 5
mA
1.5
2.4
1.5
A
A
mV/Ê
C
VIN Input Voltage
Required to
Maintain Line
Regulation
Tj = 25ÊC, IO  1A 14.6 v
0ÊC  TJ  125ÊC unless otherwise noted.
Table No. – 4

52
 Electrical Characteristics of LM7805–
Output Voltage 12V
VO Output Voltage Tj = 25ÊC, 5 mA  IO  1A 4.8 5 5.2 V
PD  15W, 5 mA  IO  1A 4.75 5.25 V
V
MIN  V
IN  V
MAX (7.5  VIN  V
VO Line Regulation IO = 500 Tj = 25ÊC 3 50 mV
mA
VIN (7  VIN  25) V
0ÊC  Tj  +125ÊC 50 mV
VIN (8  VIN  20) V
IO 1A Tj = 25ÊC 50 mV
V
IN (7.5  VIN  V
20)
0ÊC  Tj  +125ÊC 25 mV
VIN
(8  VIN  12) V
VO Load Regulation Tj = 25ÊC 5 mA  IO  1.5A 10 50 mV
250 mA  IO  25 mV
750 Ma
5 mA  IO  1A, 0ÊC  Tj  50 mV
+125ÊC
I
Q Quiescent Current IO  1A Tj = 25ÊC 8 mA
0ÊC  Tj  +125ÊC 8.5 mA
IQ Quiescent Current 5 mA  IO  1A 0.5 mA
Change Tj = 25ÊC, IO 1A 1.0 mA
V
MIN  V
IN  V
MAX (7.5  VIN 20) V
IO  500 mA, 0ÊC  Tj  +125ÊC 1.0 mA
V
MIN  V
IN  V
MAX (7  VIN 25) V

53
Output Voltage 12V
VN Output Noise TA =25ÊC, 10 Hz  f  100 kHz 40 µV
Voltage
Ripple Rejection IO  1A, Tj = 25ÊC 62 78 dB
Or
f = 120 Hz IO  500 mA 62 dB
0ÊC Tj  +125ÊC
V
MIN  V
IN  V
MAX (8  VIN  18) V
RO Dropout Voltage Tj = 25ÊC, IOUT = 1A 2.0 V
Output Resistance f = 1 kHz 8 m
Short-Circuit
Current
Peak Output
Current
Average TC of
VOUT
Tj = 25ÊC
Tj = 25ÊC
0ÊC  Tj  +125ÊC, Io = 5
mA
2.1
2.4
0.6
A
A
mV/Ê
C
VIN Input Voltage
Required to
Maintain Line
Regulation
Tj = 25ÊC, IO  1A 7.5 v
0ÊC  TJ  125ÊC unless otherwise noted.
Table No. – 5

54
2.7.3. AND Gate (IC7408):
The AND gate is a basic digital logic gate that implements logical conjunction - it behaves
according to the truth table to the right. A HIGH output (1) results only if both the inputs to the
AND gate are HIGH (1). If neither or only one input to the AND gate is HIGH, a LOW output
results. In another sense, the function of AND effectively finds the minimum between two
binary digits, just as the OR function finds the maximum. Therefore, the output is always 0
except when all the inputs are 1.
Input Output
A B A AND B
0 0 0
0 1 0
1 0 1
1 1 1
Table No. 6
 Symbols-
There are three symbols for AND gates: the American (ANSI or 'military') symbol and the IEC
('European' or 'rectangular') symbol, as well as the deprecated DIN symbol.
Fig. No. – 36
AND gate with inputs A and B and output C implements the logical expression .
MIL/ANSI Symbol IEC Symbol DIN Symbol

55
 Pin Diagram of IC7408-
Fig. No. – 37
 Electrical Characteristics -
Over recommended operating free air temperature range (unless otherwise noted)
Symbol Parameter Conditions Min TVP Max Units
VI Input Clamp
Voltage
vCC = Min, I. = -12
mA -1.5 V
VOH High Level
Output
Voltage
VCC = Min, IOH =
Max
VIL = Max
2.4 3.4
V
VOL Low Level
Output
Voltage
VGC = Min, ICL =
Max VIH = Min
0.2 0.4 V
II Input Current
@ Max Input
Voltage
vcc = Max, VI =
5.5V mA

56
IOH High Level
Input Current
vCC = Max, VI =
2.4V
40 uA
IOL Low Level
Input Current
vac = Max, v, =
0.4V -1.6 mA
IOS Short Circuit
Output
Current
Vcc = Max DM54
(Note 3) DM74
-20 -55
mA
-18 -55
ICCH Supply
Current with
Outputs High
Vcc=Max
11 21 mA
ICCL Supply
Current with
Outputs Low
Vcc=Max
20 33 mA
Table No. – 7

57
 Switching Characteristics-
At Voc = 5V and TA = 25°C
Symbol Parameter Conditions Max Units
tPLH Propagation Delay Time Low to High Level
Output
c:L =15 pF
RL = 4009
27 HS
tPHL
Propagation Delay Time High to Low Level
Output
19 HS
Table No. – 8
 Absolute Maximum Ratings-
Supply Voltage 7V ,
Input Voltage 5.5V,
Operating Free Air Temperature Range 0°C to +70°C,
Storage Temperature Range -65°C to +150°C

58
2.7.4. NOT Gate (IC7404):
In digital logic, an inverter or NOT gate is a logic gate which implements logical negation.
Input Output
A NOT A
0 1
1 0
Table No. – 9
 Symbols-
Fig. No. – 38
NOT gate with input A and output B implements the logical expression A = NOT A.
 Pin Diagram of IC7408-
Fig. No. – 39

59
 Electrical Characteristics-
Over recommended operating free air temperature range.
Symbols Parameter Conditions Min TVP Max volts
VI Input Clamp
Voltage
Vcc = Min,
II =-12 mA
-1.5 V
VOH High Level
output
Voltage
Vcc = Min,
IOH = Max
VIL = Max
2.4 3.4 V
VOL Low Level
output
Voltage
VCC = Min, IOL
= Max
VIH = Min
0.2 0.4 V
II Input Current
@ Max Input
Voltage
VCC = Max,
VL = 5.5V
1 mA
IOH HIGH Level
Input Current
Vcc =Max,
VI= 2.4V
40 uA
IIL Low Level
Input Current
Vcc =Max,
VI = 0.4V
1.6 mA
IOS Short Circuit
Output
Current
Vcc = Max
(Note 3)
-18 -55 mA
ICCH supply
Current With
Outputs High
Vcc = Max
6 12 mA

60
ICCL Supply
Current with
Outputs Low
VCC = Max 18 33 mA
Table No. – 10
 Switching Characteristics-
At Vcc = 5v and TA = 25°C
Symbols Parameter Conditions Min Max volts
tPLH Propagation Delay
Time LOW-to-
HIGH Level
Output
CF = 15 PF
RL=500 
22 ns
tPHL
Propagation Delay
Time
HlGH-to-LOW
Level Output
15 ns
Table No. – 11
 Absolute Maximum Ratings-
Supply Voltage 7V,
Input Voltage 5.5V,
Operating Free Air Temperature Range 0°C to +70°C,
Storage Temperature Range -65°C to +150°C.

61
2.8. Potentiometer:
A potentiometer, informally a pot, is a three-terminal resistor with a sliding or rotating contact
that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper,
it acts as a variable resistor or rheostat.
The measuring instrument called a potentiometer is essentially a voltage divider used for
measuring electric potential (voltage); the component is an implementation of the same
principle, hence its name.
Potentiometers are commonly used to control electrical devices such as volume controls on
audio equipment. Potentiometers operated by a mechanism can be used as position transducers,
for example, in a joystick. Potentiometers are rarely used to directly control significant power
(more than a watt), since the power dissipated in the potentiometer would be comparable to the
power in the controlled load.
Fig. No. - 40
A Typical Potentiometer
Electronic Symbol
International
US
Fig. No. - 41

62
 Potentiometer Construction:
Potentiometers consist of a resistive element, a sliding contact (wiper) that moves along the
element, making good electrical contact with one part of it, electrical terminals at each end of
the element, a mechanism that moves the wiper from one end to the other, and a housing
containing the element and wiper.
Fig. No. - 42
Drawing of potentiometer with case cut away
See drawing. Many inexpensive potentiometers are constructed with a resistive element (B)
formed into an arc of a circle usually a little less than a full turn and a wiper (C) sliding on this
element when rotated, making electrical contact. The resistive element can be flat or angled.
Each end of the resistive element is connected to a terminal (E, G) on the case. The wiper is
connected to a third terminal (F), usually between the other two. On panel potentiometers, the
wiper is usually the centre terminal of three. For single-turn potentiometers, this wiper typically
travels just under one revolution around the contact. The only point of ingress for
contamination is the narrow space between the shaft and the housing it rotates in.
Another type is the linear slider potentiometer, which has a wiper which slides along a linear
element instead of rotating. Contamination can potentially enter anywhere along the slot the
slider moves in, making effective sealing more difficult and compromising long-term
reliability. An advantage of the slider potentiometer is that the slider position gives a visual
indication of its setting. While the setting of a rotary potentiometer can be seen by the position
of a marking on the knob, an array of sliders can give a visual impression of, for example, the
effect of a multi-band equalizer.

63
Fig No. - 43
Single-turn potentiometer with metal casing removed to expose wiper contacts and resistive
track
The resistive element of inexpensive potentiometers is often made of graphite. Other materials
used include resistance wire, carbon particles in plastic, and a ceramic/metal mixture called
cermet. Conductive track potentiometers use conductive polymer resistor pastes that contain
hard-wearing resins and polymers, solvents, and lubricant, in addition to the carbon that
provides the conductive properties.
Resistance–position relationship: "taper"
The relationship between slider position and resistance, known as the "taper" or "law", is
controlled by the manufacturer. In principle any relationship is possible, but for most purposes
linear or logarithmic potentiometers are sufficient.
 Linear taper potentiometer-
A linear taper potentiometer has a resistive element of constant cross-section, resulting in a
device where the resistance between the contact (wiper) and one end terminal is proportional
to the distance between them. Linear taper potentiometers are used when the division ratio of
the potentiometer must be proportional to the angle of shaft rotation (or slider position), for
example, controls used for adjusting the centering of the display on an analog cathode-ray
oscilloscope. Precision potentiometers have an accurate relationship between resistance and
slider position.

64
 Logarithmic potentiometer-
A logarithmic taper potentiometer has a resistive element that either 'tapers' in from one end to
the other, or is made from a material whose resistivity varies from one end to the other. This
results in a device where output voltage is a logarithmic function of the slider position.
Most "log" potentiometers are not accurately logarithmic, but use two regions of different
resistance to approximate a logarithmic law. The two resistive tracks overlap at approximately
50% of the potentiometer rotation; this gives a stepwise logarithmic taper. A logarithmic
potentiometer can also be simulated (not very accurately) with a linear one and an external
resistor. True logarithmic potentiometers are significantly more expensive.
 Theory Of Operation-
Fig. No. - 44
A potentiometer with a resistive load, showing equivalent fixed resistors for clarity
The potentiometer can be used as a voltage divider to obtain a manually adjustable output
voltage at the slider (wiper) from a fixed input voltage applied across the two ends of the
potentiometer. This is their most common use.
The voltage across RL can be calculated by:

65
If RL is large compared to the other resistances (like the input to an operational amplifier), the
output voltage can be approximated by the simpler equation:
(Dividing throughout by RL and cancelling terms with RL as denominator)
 Advantages-
One of the advantages of the potential divider compared to a variable resistor in series with the
source is that, while variable resistors have a maximum resistance where some current will
always flow, dividers are able to vary the output voltage from maximum (VS) to ground (zero
volts) as the wiper moves from one end of the potentiometer to the other. There is, however,
always a small amount of contact resistance.
In addition, the load resistance is often not known and therefore simply placing a variable
resistor in series with the load could have a negligible effect or an excessive effect, depending
on the load.

66
2.9. Transistor:
A transistor is a semiconductor device used to amplify or switch electronic signals and
electrical power. It is composed of semiconductor material with at least three terminals for
connection to an external circuit. A voltage or current applied to one pair of the transistor's
terminals changes the current through another pair of terminals. Because the controlled (output)
power can be higher than the controlling (input) power, a transistor can amplify a signal. Today,
some transistors are packaged individually, but many more are found embedded in integrated
circuits.
Fig. No. - 45
Transistor CL100
The transistor is the fundamental building block of modern electronic devices, and is ubiquitous
in modern electronic systems. First conceived by Julius Lilienfeld in 1926 and practically
implemented in 1947 by American physicists John Bardeen, Walter Brattain, and William
Shockley, the transistor revolutionized the field of electronics, and paved the way for smaller
and cheaper radios, calculators, and computers, among other things. The transistor is on the list
of IEEE milestones in electronics, and Bardeen, Brattain, and Shockley shared the 1956 Nobel
Prize in Physics for their achievement.
 Simplified operation-
The essential usefulness of a transistor comes from its ability to use a small signal applied
between one pair of its terminals to control a much larger signal at another pair of terminals.
This property is called gain. It can produce a stronger output signal, a voltage or current, which
is proportional to a weaker input signal; that is, it can act as an amplifier. Alternatively, the
transistor can be used to turn current on or off in a circuit as an electrically controlled switch,
where the amount of current is determined by other circuit elements.

67
There are two types of transistors, which have slight differences in how they are used in a
circuit. A bipolar transistor has terminals labeled base, collector, and emitter. A small current
at the base terminal (that is, flowing between the base and the emitter) can control or switch a
much larger current between the collector and emitter terminals. For a field-effect transistor,
the terminals are labeled gate, source, and drain, and a voltage at the gate can control a current
between source and drain.
Fig. No. - 46
A simple circuit diagram to show the labels of an n–p–n bipolar transistor.
The image represents a typical bipolar transistor in a circuit. Charge will flow between emitter
and collector terminals depending on the current in the base. Because internally the base and
emitter connections behave like a semiconductor diode, a voltage drop develops between base
and emitter while the base current exists. The amount of this voltage depends on the material
the transistor is made from, and is referred to as VBE.

68
 A Bipolar NPN Transistor Configuration-
Fig. No. – 47
Arrow defines the emitter and conventional current flow, “out” for a Bipolar NPN Transistor.
The construction and terminal voltages for a bipolar NPN transistor are shown above. The
voltage between the Base and Emitter (VBE), is positive at the Base and negative at the Emitter
because for an NPN transistor, the Base terminal is always positive with respect to the Emitter.
Also the Collector supply voltage is positive with respect to the Emitter (VCE ). So for a bipolar
NPN transistor to conduct the Collector is always more positive with respect to both the Base
and the Emitter.
Fig. No. - 48
NPN Transistor Connection
Then the voltage sources are connected to an NPN transistor as shown. The Collector is
connected to the supply voltage VCC via the load resistor, RL which also acts to limit the
maximum current flowing through the device. The Base supply voltage VB is connected to the
Base resistor RB, which again is used to limit the maximum Base current.

69
So in a NPN Transistor it is the movement of negative current carriers (electrons) through the
Base region that constitutes transistor action, since these mobile electrons provide the link
between the Collector and Emitter circuits. This link between the input and output circuits is
the main feature of transistor action because the transistors amplifying properties come from
the consequent control which the Base exerts upon the Collector to Emitter current.
Then we can see that the transistor is a current operated device (Beta model) and that a large
current (IC ) flows freely through the device between the collector and the emitter terminals
when the transistor is switched “fully-ON”. However, this only happens when a small biasing
current (IB) is flowing into the base terminal of the transistor at the same time thus allowing
the Base to act as a sort of current control input.
The transistor current in a bipolar NPN transistor is the ratio of these two currents (IC/I ), called
the DC Current Gain of the device and is given the symbol of Beta. Also, the current gain of
the transistor from the Collector terminal to the Emitter terminal, Ic/IB, is called Alpha.

70
 Input and Output Characteristics of Transistor-
To fully describe the behaviour of a three-terminal device such as the common-base amplifiers
requires two sets of characteristics – one for the driving point or input parameters and the other
for the output side. The input set for the common-base amplifier relates an input current (IE) to
an input voltage (VBE) for various levels of output voltage (VCB).
Fig. No. – 49
Input or driving characteristics
The output set relates an output current (IC) to an output voltage (VCB) for various levels of
input current (IE).The output or collector set of characteristics has three basic region of interest
, as indicated in figure : the active , cut-off and saturation regions.
Fig. No. – 50
Output or collector characteristics

71
2.10. Hall Effect Current Sensor (ACS712):
A current sensor is a device that detects electric current (AC or DC) in a wire, and generates a
signal proportional to it. The generated signal could be analog voltage or current or even digital
output. It can be then utilized to display the measured current in an ammeter or can be stored
for further analysis in a data acquisition system or can be utilized for control purpose.
The sensed current and the output signal can be:
 Alternating current input,
1. analog output, which duplicates the wave shape of the sensed current
2. bipolar output, which duplicates the wave shape of the sensed current
3. unipolar output, which is proportional to the average or RMS value of the
sensed current
 Direct current input,
1. unipolar, with a unipolar output, which duplicates the wave shape of the
sensed current
2. Digital output, which switches when the sensed current exceeds a certain
threshold.
 CURRENT SENSING PRINCIPLES-
A current sensor is a device that detects and converts current to an easily measured output
voltage, which is proportional to the current through the measured path.
When a current flows through a wire or in a circuit, voltage drop occurs. Also, a magnetic field
is generated surrounding the current carrying conductor. Both of these phenomena are made
use of in the design of current sensors. Thus, there are two types of current sensing: direct and
indirect. Direct sensing is based on Ohm’s law, while indirect sensing is based on Faraday’s
and Ampere’s law.
Direct Sensing involves measuring the voltage drop associated with the current passing through
passive electrical components.

72
Indirect Sensing involves measurement of the magnetic field surrounding a conductor
through which current passes.
Fig. No. - 51
Generated magnetic field is then used to induce proportional voltage or current which is then
transformed to a form suitable for measurement and/or control system.
 Hall Effect-
The Hall Effect is the production of a voltage difference (the Hall voltage) across an electrical
conductor, transverse to an electric current in the conductor and a magnetic field perpendicular
to the current. It was discovered by Edwin Hall in 1879.
The Hall coefficient is defined as the ratio of the induced electric field to the product of the
current density and the applied magnetic field. It is a characteristic of the material from which
the conductor is made, since its value depends on the type, number, and properties of the charge
carriers that constitute the current.
Fig. No. – 52
Electromagnetism
Theory-
The Hall Effect is due to the nature of the current in a conductor. Current consists of the
movement of many small charge carriers, typically electrons, holes, ions or all three. When a
magnetic field is present, these charges experience a force, called the Lorentz force. When such

73
a magnetic field is absent, the charges follow approximately straight, 'line of sight' paths
between collisions with impurities, phonons, etc. However, when a magnetic field with a
perpendicular component is applied, their paths between collisions are curved so that moving
charges accumulate on one face of the material. This leaves equal and opposite charges exposed
on the other face, where there is a scarcity of mobile charges. The result is an asymmetric
distribution of charge density across the Hall element, arising from a force that is perpendicular
to both the 'line of sight' path and the applied magnetic field. The separation of charge
establishes an electric field that opposes the migration of further charge, so a steady electrical
potential is established for as long as the charge is flowing.
In classical electromagnetism electrons move in the opposite direction of the current I (by
convention "current" describes a theoretical "hole flow"). In some semiconductors it appears
"holes" are actually flowing because the direction of the voltage is opposite to the derivation
below.
Fig. No. – 53
Hall Effect measurement setup for electrons. Initially, the electrons follow the curved arrow,
due to the magnetic force. At some distance from the current-introducing contacts, electrons pile up on
the left side and deplete from the right side, which creates an electric field ξy in the direction of the
assigned VH. VH is negative for some semi-conductors where "holes" appear to flow. In steady-state,
ξy will be strong enough to exactly cancel out the magnetic force, so that the electrons follow the straight
arrow (dashed).
For a simple metal where there is only one type of charge carrier (electrons) the Hall voltage
VH can be derived by using the Lorentz force and seeing that in the steady-state condition
charges are not moving in the y-axis direction because the magnetic force on each electron in
the y-axis direction is cancelled by an y-axis electrical force due to the build-up of charges.
The Vx term is the drift velocity of the current which is assumed at this point to be holes by

74
convention. The VxBz term is negative in the y-axis direction by the right hand rule.
Where is assigned in direction of y-axis, not with the arrow as in the image.
In wires, electrons instead of holes are flowing, so and . Also .
Substituting these changes gives
The conventional "hole" current is in the negative direction of the electron current and the negative of the
electrical charge which gives where is charge carrier density , is the
cross-sectional area, and is the charge of each electron. Solving for and plugging into the above gives
the Hall voltage:
the charge build-up had been positive (as it appears in some semiconductors), then the assigned in the
image would have been negative (positive charge would have built up on the left side).
The Hall coefficient is defined as
where j is the current density of the carrier electrons, and is the induced electric field. In
SI units, this becomes
(The units of RH are usually expressed as m3
/C, or Ω·cm/G, or other variants.) As a result, the Hall
effect is very useful as a means to measure either the carrier density or the magnetic field.
Applications-
Hall probes are often used as magnetometers, i.e. to measure magnetic fields, or inspect
materials (such as tubing or pipelines) using the principles of magnetic flux leakage.

75
Hall Effect devices produce a very low signal level and thus require amplification. While
suitable for laboratory instruments, the vacuum tube amplifiers available in the first half of the
20th century were too expensive, power consuming, and unreliable for everyday applications.
It was only with the development of the low cost integrated circuit that the Hall Effect sensor
became suitable for mass application. Many devices now sold as Hall Effect sensors in fact
contain both the sensor as described above plus a high gain integrated circuit (IC) amplifier in
a single package. Recent advances have further added into one package an analog-to-digital
converter and I²C (Inter-integrated circuit communication protocol) IC for direct connection to
a microcontroller's I/O port.
 Specifications-
 Low value in order to minimize power losses-
Value of the current sense resistors primarily depend upon the voltage threshold of the
following circuitry which is going to operate based upon the sensed current information.
In circuits where amplification is available, emphasis is to minimize the voltage drop
across the resistor.
 Low inductance because of high di/dt-
Any inductance in the resistor, when exposed to high slew rate (di/dt), an inductive step
voltage is superimposed upon the sense voltage and may be a cause of concern in many
circuits. Hence sense resistors should have very low inductance.
 Tight tolerance
For maximizing the current supply within the limit of acceptable current, the tolerance
of the sense resistor must be ±1% or tighter
 Low temperature coefficient for accuracy
Normally specified in units of parts per million per degree centigrade (ppm/°C),
temperature coefficient of resistance (TCR) is an important parameter for accuracy.
Resistors with TCRs closer to zero, in the entire operating range should be used.
 High peak power rating to handle short duration high current pulses-
Power rating is a driving factor for the selection of appropriate technology for sense
resistors. Though the device may be intended to sense DC current, it may often
experience transients.

76
Power derating curve provides allowable power at different temperatures. But peak
power capability is a function of energy; hence energy rating curve should be taken
into account
 High temperature rating for reliability
 Advantages of Current Sensors-
1. Low cost
2. High measurement accuracy
3. Measurable current range from very low to medium
4. Capability to measure DC or AC current
 Disadvantages of Current Sensors-
1. Introduces additional resistance into the measured circuit path, which may
increase source output resistance and result in undesirable loading effect.
2. Power loss due to power dissipation. Therefore, current sensing resistors are
rarely used beyond the low and medium current sensing applications.

77
2.11. Relay:
A relay is an electrically operated switch. Many relays use an electromagnet to mechanically
operate a switch, but other operating principles are also used, such as solid-state relays. Relays
are used where it is necessary to control a circuit by a low-power signal (with complete
electrical isolation between control and controlled circuits), or where several circuits must be
controlled by one signal. The first relays were used in long distance telegraph circuits as
amplifiers: they repeated the signal coming in from one circuit and re-transmitted it on another
circuit. Relays were used extensively in telephone exchanges and early computers to perform
logical operations.
Fig. No. – 54
Automotive type miniature relay, dust cover is taken off
A type of relay that can handle the high power required to directly control an electric motor or
other loads is called a contactor. Solid-state relays control power circuits with no moving parts,
instead using a semiconductor device to perform switching. Relays with calibrated operating
characteristics and sometimes multiple operating coils are used to protect electrical circuits
from overload or faults; in modern electric power systems these functions are performed by
digital instruments still called "protective relays".
 Basic design and operation-
Simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an
iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature,
and one or more sets of contacts. The armature is hinged to the yoke and mechanically linked
to one or more sets of moving contacts. It is held in place by a spring so that when the relay is
de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of

78
contacts in the relay pictured is closed, and the other set is open. Other relays may have more
or fewer sets of contacts depending on their function. The relay in the picture also has a wire
connecting the armature to the yoke. This ensures continuity of the circuit between the moving
contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which
is soldered to the PCB.
Fig. No. – 55
Small "cradle" relay often used in electronics. The "cradle" term refers to the shape of the
relay's armature.
When an electric current is passed through the coil it generates a magnetic field that activates
the armature, and the consequent movement of the movable contact(s) either makes or breaks
(depending upon construction) a connection with a fixed contact. If the set of contacts was
closed when the relay was de-energized, then the movement opens the contacts and breaks the
connection, and vice versa if the contacts were open. When the current to the coil is switched
off, the armature is returned by a force, approximately half as strong as the magnetic force, to
its relaxed position. Usually this force is provided by a spring, but gravity is also used
commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a
low-voltage application this reduces noise; in a high voltage or current application it
reduces arcing.
 Pole and throw-
Normally open (NO) contacts connect the circuit when the relay is activated; the circuit is
disconnected when the relay is inactive. It is also called a "Form A" contact or "make" contact.
NO contacts may also be distinguished as "early-make" or "NOEM", which means that the
contacts close before the button or switch is fully engaged.

Motor Burnout and Under voltage protection

Motor Burnout and Under voltage protection

Recommended

Recommended

More Related Content

What's hot

What's hot (19)

Similar to Motor Burnout and Under voltage protection

Similar to Motor Burnout and Under voltage protection (20)

Recently uploaded

Recently uploaded (20)

Motor Burnout and Under voltage protection