TAGORE INSTITUTE OF ENGINEERING AND

TECHNOLOGY
Deviyakurichi-636112, Thalaivasal (TK), Salem (DT). Website: www.tagoreiet.ac.in
Approved by AICTE, New Delhi and Affiliated to Anna University, Chennai
Accredited by NAAC
1
QUESTION BANK
Name of the Department : Electrical and Electronics Engineering
Subject Code & Name : EE3402 & Linear Integrated Circuits
Year & Semester : III YEAR & V SEM

UNIT-I
1. Mention the advantages of integrated circuits.
 Miniaturisation and hence increased equipment density.
 Cost reduction due to batch processing.
 Increased system reliability due to the elimination of soldered joints.
 Improved functional performance.
 Matched devices.
 Increased operating speeds
 Reduction in power consumption
2. Write down the various processes used to fabricate IC’s using silicon planar technology.
 Silicon wafer preparation.
 Epitaxial growth
 Oxidation.
 Photolithography.
 Diffusion.
 Ion implantation.
 Isolation.
 Metallisation.
 Assembly processing and packaging
3. What is the purpose of oxidation?
 SiO2 is an extremely hard protective coating and is unaffected by almost all reagents.
 By selective etching of SiO2, diffusion of impurities through carefully defined windows can be
accomplished to fabricate various components.
4. Why aluminum is preferred for metallization?
 It is a good conductor.
 it is easy to deposit aluminium films using vacuum deposition.
 It makes good mechanical bonds with silicon.
 It forms a low resistance contact.
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TECHNOLOGY
Deviyakurichi-636112, Thalaivasal (TK), Salem (DT). Website: www.tagoreiet.ac.in
Approved by AICTE, New Delhi and Affiliated to Anna University, Chennai
Accredited by NAAC
5. What are the popular IC packages available?
2
a. Metal can package.
b. Dual-in-line package.
c. Ceramic flat package
PART – B

1. Explain the process of epitaxial growth in IC fabrication process with neat diagrams.

2 Describe in detail about the diffusion process of IC fabrication.

3 Write a note on isolation technique used in ICs.

4 Discuss the different ways to fabricate diodes.

5 Explain in detail the fabrication process of passive component in integrated circuits.

6. Explain the basic processes used in the fabrication of monolithics IC.

7 Explain the process of epitaxial growth in IC fabrication process with neat diagrams.

8. Explain the importance of isolation and discuss the different methods of isolation.

9. How a PN junction diode is formed in IC fabrication

10. Explain the process of masking and photoetching in IC fabrication.

11. Explain the different types of IC packages.

12. Briefly explain the various process involved in fabrication monolithic IC which integrates
diode capacitance and FET. .

13. Explain in detail about the Photolithography process with neat diagram.

14. With circuit diagram explain the steps involved in the fabrication of the circuit shown below
using IC technology.
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Approved by AICTE, New Delhi and Affiliated to Anna University, Chennai
Accredited by NAAC
3

15.Explain the basic process used in silicon planar technology with neat diagram.

16. Write a note on classification of IC and IC packages.

17.Explain in detail the recent fabrication methods of diode and capacitance for industrial
applications.

18. Describe the steps involved in the fabrication of monolithic IC transistors.

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4
UNIT-II

1. Draw the op-amp symbol and state its important terminals.

Ans. : For the op-amp symbol, refer the Fig. 2.2.1. The important terminals are,

1. Positive supply 2. Negative supply 3. Output 4. Inverting input 5. Noninverting

input.

2.Which circuits are commonly used for the various stages of an 1C op-amp ?

1. Internal stage : Dual input balanced output differential amplifier.

2Intermediate stage : Multistage amplifiers without coupling capacitors and

single ended

3. Level shifting stage : Various transistor circuits to reduce the d.c. output
level.

4. Output stage: Push-pull complementary symmetry amplifier in Class AB

operation.

3. List the requirements of the internal stage of IC op-amp.

Ans. : 1. High voltage gain 2. High input impedance 3. Two input terminals

4. Small offset voltages 5. Small offset currents 6. High CMRR.

4. List the requirements of the output stage of IC op-amp.

Ans. : 1. High output voltage swing 2. High output current swing 3. Low output
impedance 4. Low quiescent power dissipation 5. Various protection circuits.

5. List the important characteristics of ideal op-amp.

Ans. : 1. Infinite voltage gain 2. Infinite input impedance 3. Zero output impedance

4. Infinite bandwidth 5. Infinite CMRR 6. Infinite slew rate 7. Zero PSRR

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6. Draw the equivalent circuit of practical op-amp. 5
Ans. :

7. What is input offset voltage ?

Ans. : When both the input terminals of the op-amp are grounded, ideally the output
should be zero. But practically op-amp produces the small output voltage. To nullify
this voltage, some voltage is required to be applied to either of the two input
terminals in the particular direction. This voltage is called input offset voltage.

How much voltage, to which input and with what polarity is specified by the
manufacturer in the data sheet of the op-amp.

8. What is input bias current and input offset current ?

Ans. : The base currents of the transistors used in the input stage of the differential
amplifier are practically finite and the two currents differ in magnitude as perfect
matched transistors are not possible in practice. These currents are responsible for
the input bias current and input offset current of op-amp.

The input bias current is the average of the two base currents Ib,and Ib2 while the
input offset current is the difference between the two base currents Ib,^d Ib2.

9. What is output offset voltage ? Which parameters are responsible to produce

it ?
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Ans. : The output voltage present when both the input terminals of the op- 6
amp are grounded is called output offset voltage. The input offset voltage,
input bias current and input offset current are responsible to produce output offset
voltage.

10.What is thermal drift ?

Ans. : The dependence of the op-amp parameters on the temperature is indicated by

a factor called temperature drift. The change in the op-amp parameter corresponding
to the change in the temperature is defined as the thermal drift of that parameter.
Thus Δ Vios / ΔT is called input offset voltage temperature drift.

11.What is PSRR ? What should be its ideal value ?

Ans. : PSRR is power supply rejection ratio. It is defined as the change in the input
offset voltage due to the change in one of the two supply voltages when other
voltage is maintained constant Its ideal value should be zero.

12.What is slew rate ? State slew rate equation.

Ans. : The maximum rate of change of output voltage with respect to time is called
slew rate of the op-amp.

The slew rate equation is, S = 2π fVm V / sec

13.Draw the typical frequency response of the op-amp.

Ans. : Refer the Fig. 2.15.2 of the section 2.15. The students may draw it without
semilogpaper only indicating the nature of the two plots.
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7
14. Compare the ideal and practical op-amp characteristics.

Ans. :

15. What is frequency compensation ?

Ans. : The method of modifying loop gain frequency response of the op-amp so that
it behaves like single break frequency response which provides sufficient positive
phase margin is called frequency compensation technique.

16. State the advantages of voltage follower.

Ans. :

1) Very large input resistance, of the order of MQ.

2) Low output impedance, almost zero. Hence it can be used to connect high
impedance source to a low impedance load, as a buffer.

3) It has large bandwidth.

4) The output follows the input exactly without a phase shift.

17.How to obtain the average circuit from the inverting summer ?

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Ans. : In an inverting summer if the values of resistances are selected such 8
that R1 = R2 = R and Rf = R/2 then the output is the average of the two inputs
applied to the circuit

18. List the applications of integrator circuit.

Ans. : i) In the analog computers, ii) In solving differential equations, iii) In analog
to digital converters, iv) Various signal wave shaping circuits, v) In ramp and
triangular waveform generators.

19.List the applications of differentiator circuit.

Ans. : i) In the wave shaping circuits, ii) To detect high frequency components in
the input, iii) As a rate of change detector in the FM demodulators.

20.In an inverting amplifier the values of Rf and R1 are 100 kΩ and 10 kΩ

respectively. What is the gain of the amplifier?

Ans : Gain of the inverting amplifier is given by – Rf / R1 = - 100 / 10 = -10.

PART-B
1.List the dc and ac characteristics of opamp and define each of them.
2. Write a technical note on frequency response characteristics of opamp.
3. Define slew rate. Explain the causes of slew rate. Derive slew rate equation for opamp
voltage follower.
4. Draw and explain the summing amplifier.
5. With the circuit diagram explain the operation of an integrator.
6. Derive an expression for the output of a practical differentiator.
7. Explain the application of opamp as a differentiator.
8. Draw and explain practical opamp equivalent circuit.
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9. Draw and explain the circuit of a voltage to current converter if the load is floating and
9
grounded.
10. Draw an adder -subtractor type of circuit with opamp to obtain the relation
Vo=(V1+V2)-(V3=V4).

UNIT-III
1.Mention some of the linear applications of op – amps.

 Adder,

 subtractor,

 voltage –to- current converter,

 current –to- voltage converters,

 instrumentation amplifier,

 analog computation ,

 power amplifier, etc are some of the linear op-amp circuits.

2.Mention some of the non – linear applications of op-amps:-

 Rectifier,

 peak detector,

 clipper,

 clamper,

 sample and hold circuit,

 log amplifier,

 anti –log amplifier,

 multiplier are some of the non – linear op-amp circuits.

3. What is the need for an instrumentation amplifier?

In a number of industrial and consumer applications, the measurement of physical quantities is

usually done with the help of transducers. The output of transducer has to be amplified So that it can drive
the indicator or display system. This function is performed by an instrumentation amplifier.

4. List the features of instrumentation amplifier: ”

 high gain accuracy

 high CMRR
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 high gain stability with low temperature co-efficient
10
 low dc offset

 low output impedance

5. What are the applications of V-I converter? ”

 Low voltage dc and ac voltmeter ”

 LED”
 Zener diode test
6. What do you mean by a precision diode?

The major limitation of ordinary diode is that it cannot rectify voltages below the cut – in voltage of the
diode. A circuit designed by placing a diode in the feedback loop of an op – amp is called the precision
diode and it is capable of rectifying input signals of the order of millivolt.

7. Write down the applications of precision diode. ”

 Half - wave rectifier

 Full - Wave rectifier

 Peak – value detector

 Clipper

 Clamper

8. List the applications of Log amplifiers:

Analog computation may require functions such as lnx, log x, sin hx etc. These functions can be
performed by log amplifiers ” Log amplifier can perform direct dB display on digital voltmeter and
spectrum analyzer ” Log amplifier can be used to compress the dynamic range of a signal

9. What are the limitations of the basic differentiator circuit?

At high frequency, a differentiator may become unstable and break into oscillations ”

The input impedance decreases with increase in frequency , thereby making the circuit sensitive to high
frequency

10. Write down the condition for good differentiation :-

For good differentiation, the time period of the input signal must be greater than or equal to Rf C1 T > R f
C1 Where, Rf is the feedback resistance Cf is the input capacitance

11. What is a comparator?

comparator is a circuit which compares a signal voltage applied at one input of an op-amp with a known
reference voltage at the other input. It is an open loop op - amp with output + Vsat .
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Approved by AICTE, New Delhi and Affiliated to Anna University, Chennai
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12. What are the applications of comparator? ”
11
 Zero crossing detector ”

 Window detector ”

 Time marker generator ”

 Phase detector

13. What is a Schmitt trigger?

Schmitt trigger is a regenerative comparator. It converts sinusoidal input into a square wave output. The
output of Schmitt trigger swings between upper and lower threshold voltages, which are the reference
voltages of the input waveform.

14. What is a multivibrator?

Multivibrators are a group of regenerative circuits that are used extensively in timing applications. It is a
wave shaping circuit which gives symmetric or asymmetric square output. It has two states either stable or
quasi- stable depending on the type of multivibrator.

15.What do you mean by monostable multivibrator?

Monostable multivibrator is one which generates a single pulse of specified duration in response to each
external trigger signal. It has only one stable state. Application of a trigger causes a change to the quasi-
stable state. An external trigger signal generated due to charging and discharging of the capacitor produces
the transition to the original stable state.

16.What is an astable multivibrator?

Astable multivibrator is a free running oscillator having two quasi-stable states. Thus, there is oscillations
between

17.What is a bistable multivibrator?

Bistable multivibrator is one that maintains a given output voltage level unless an external trigger is
applied. Application of an external trigger signal causes change of state, and this output level is maintained
indefinitely until an second trigger is applied. Thus, it requires two external triggers before it returns to its
initial state

18.Mention any two audio frequency oscillators:

 RC phase shift oscillator ”

 Wein bridge oscillator
19. What are the advantages of active filters?

Active filters used op- amp as the active element and resistors and capacitors as passive elements. By
enclosing a capacitor in the feedback loop, inductor less active filters can be obtained-amp used in non –
inverting configuration offers high input impedance and low output impedance, thus improving the load
drive capacity.

20. Mention some commonly used active filters : ”

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 Low pass filter
12
 High pass filter ”

 Band pass filter ”

 Band reject filter

PART-B
1. Draw the circuit of monostable multivibrator and obtain the expression for pulse width.
2. Explain the operation of opamp as a clamper
3. Draw and explain the operation of a triangular wave generator and obtain the expression for its
frequency.
4. Explain the working of peak detector using operational amplifier.
5. Explain the working of sample and hold circuits.
6. Compare the performance of various type of ADC.
7. Explain in detail about R-2R ladder DAC and inverted R-2R ladder DAC along with relevant
circuit diagrams and waveforms.
8. Explain the working of opamp as a Comparator.
9. Explain with neat diagram, the operation of narrow band pass filter.
10. Explain with neat diagram, the operation of first order pass Butterworth filter.

UNIT-IV
PART-A

1. What is a function of reset pin 4 in 555 timer ?

Ans. : This is an interrupt to the timing device. When pin 4 is grounded, it stops the
working of device and makes it off. Thus, pin 4 provides on/off feature to the IC
555. This reset input overrides all other functions within the timer when it is
momentarily grounded.

2. List any four applications of analog multipliers.

Ans. : 1. In communication it is used in amplitude modulation, phase modulation,

frequency modulation, phase detection, suppressed carrier modulation etc.
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2. In instrumentation and control used to measure velocity, acceleration, 13
instantaneous power, automatic gain control, etc.

3. For voltage controlled attenuators and for voltage controlled amplification.

4. It is used for voltage divider, true r.m.s calculation, rectifier phase shift detection
etc.

5. It is used for frequency converters, frequency doubling and frequency shifting etc.

6. It is used for squaring and square root calculations.

3. Enlist the important features of 555 timer circuit.

Ans. :

1. The 555 is a monolithic timer device which can be used to produce accurate and
highly stable time delays or oscillation. It can be used to produce time delays
ranging from few microseconds to several hours.

2. It has two basic operating modes : Monostable and astable

4. List any four applications of 555 timer in astable mode of operation.

Ans. :

1. Square wave generator

2. Voltage controlled oscillator

3. FSK generator

4. Flasher circuit.

5. What is the function of pin 5, control voltage input of 555 timer ?

Ans. : If external input applied to pin 5 is alternating then the reference level for
comparator 1 keeps on changing above and below 2/3 V CC. Due to this, the variable
pulse width output is possible. This is called pulse width modulation, which is
possible due to pin 5.
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6. List any four applications of 555 timer in monostable mode of 14
operation.

Ans. :

1. Frequency divider 2. Pulse width modulation 3. Linear ramp generator

4. Pulse position modulation 5. Missing pulse detector 6. Timer for relays

7. Give the expression for the pulse width when 555 timer is used in monostable
mode.

Ans. : The expression for the pulse width when 555 timer is used in monostable
mode is, W = 1.1 RC

8. Give the expression for the time period and duty cycle when 555 timer is used
in astable mode.

Ans. : The expression for the time period and duty cycle when 555 timer is used in
astable mode is,

T = 0.693 (RA + 2 RB) C and %D = (RA + RB) / (RA + RB) × 100

9. What is one quadrant, two quadrant and four quadrant multipliers ?

Ans. : In one quadrant multiplier the polarities of both the inputs must always be
positive. In two quadrant multiplier the one input must be held positive and other is
allowed to swing in both positive and negative. While in four quadrant multiplier
both the inputs are allowed to swing in both positive and negative directions.

10. List the performance parameters of multiplier.

Ans. : 1. Accuracy 2. Linearity 3. Bandwidth 4. Feed through voltage

5. Zero trim 6. Scale factor 7. 1 % absolute error bandwidth 8. Quadrant

11. What is an analog multiplier ? State its applications.

Ans. : An analog multipliter is a circuit which produces an output voltage or curent

which is the scaled product of two voltages or currents. It is versatile functional
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device which can be used to perform various functions like product and 15
division of two signals, squaring of a signal, frequency doubling and shifting,
phase angle detection etc.

12.Explain the function of trigger, pin 2 in 1C 555 timer.

Ans. : The pin 2 in IC 555 timer is trigger. The inverting input of comparator 2 is
brought out as trigger. It is compared with [1/3 Vcc] and when it is below this level,
the output of the comparator 2 goes high which is given to reset input of R-S flip-
flop. Thus high ouput of comparator 2 resets the flip-flop.

13. What are the applications of timer IC 555.

Ans. : The timer IC 555 is designed mainly to produce accurate and stable RC
defined time periods. It is mainly used as monostable multivibrator, astable
multivibrator or as a Schmitt trigger. The monostable multivibrator using 555 has
many applications such as pulse width modulation, linear ramp generator, frequency
divider, missing pulse detector etc. The astable multivibrator using 555 has many
applications such as square wave generator, voltage controlled oscillator, FSK
generator etc.

14. Define PLL.

Ans. : A phase locked loop is basically a closed loop system designed to lock the
output frequency and phase to the frequency and phase of an input signal. It is
commonly abbreviated as PLL.

15.What is a voltage controlled oscillator ?

OR

Why VCO is called voltage to frequency converter ?

Ans. : A Voltage Controlled Oscillator (VCO) is an oscillator circuit in which the

frequency of oscillations can be controlled by an externally applied voltage. The
VCO provides the linear relationship between the applied voltage and the oscillation
frequency. As voltage controls the frequency, it is called voltage controlled
oscillator.
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16. How VCO different from oscillators ? 16
Ans. : An oscillator is circuit that generates the frequency output of fixed
frequency. On the other hand, a Voltage Controlled Oscillator (VCO) is an oscillator
circuit in which the frequency of oscillations can be controlled by an externally
applied voltage.

17.Why VCO is called voltage to frequency converter ?

Ans. : The VCO provides the linear relationship between the applied voltage and the
output frequency, hence it is also called voltage to frequency converter.

18.Define : Lock range.

Ans. : The range of frequencies over which the PLL can maintain lock with the
incoming signal is called the lock range or tracking range of the PLL.

19.Define capture range of a PLL.

Ans. : The range of frequencies over which the PLL can acquire lock with an input
signal is called the capture range.

20. Name two applications of PLL.

Ans. : PLL is used in

a. Frequency multiplier b. Frequency synthesizer c. FM demodulator

d. FSK demodulator e. AM detection f. Frequency translation

21. In the monostable multivibrator of below figure circuit R 1 = 100 kΩ and the
time delay T = 100 ms. Calculate the value C1.
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17

PART-B

1. Describe the monostable operation of 555 Timer.

2. Briefly explain the functional block diagram of PLL IC 565.

3. With circuit schematic explain how the multiplier IC AD 533 can be used as a
squarer and divider circuits.

4. What is PLL?Explain its application as a frequency multiplier.

5. Explain AM Modulation using PLL.

6. Explain the operation of square wave generator using IC555 by drawing

capacitor and output voltage waveforms.

7. Explain the applications of PLL as frequency translator and FM demodulator.

8. Derive the expression for capture range for PLL where a simple RC network is
used as a low pass filter.

9. Explain the working of voltage controlled oscillator.

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10. Draw the block diagram of basic PLL and explain the function of each 18
block.

UNIT-V
PART-A
1. What is the purpose of having input and output capacitors in three terminal ICregulators?
A capacitor connected between the input terminal and groundcancels the inductive effects due
tolong distribution leads. The output capacitor improves the transient response.
2. Define load regulation.
Load regulation is defined as the change in output voltage for a change in load current. It
isexpressed in millivolts or as a percentage of the output voltage

3. What is the advantage of switching regulators?

Greater efficiency is achieved as the power transistor is made to operate as low impedance
switch.Power transmitted across the transistor is in discrete pulses rather than as a steady current
flow.By using suitable switching loss reduction technique, the switching frequency can be
increased soas to reduce the size and weight of the inductors and capacitors.

4. Define video amplifier.

A video amplifier has to amplify signals over a wideband of frequencies, say upto 20MHz. It is a
RCcoupled amplifier with bandwidth from d.c. to high frequency upto few megahertz.
5. What is opto coupler?
An opto-isolator, also called an optocoupler, photocoupler, or optical isolator, is "an
electronicdevice designed to transfer electrical signals by utilizing light waves to providecoupling
withelectrical isolation between its input and output". The main purpose of an opto-isolator is "to
preventhigh voltages or rapidly changing voltages on one side of the circuit from damaging
components or distorting transmissions on the other side
6. How the current boosting is achieved in a IC 723.
The maximum load current of IC 723 is 150mA. If the current is to be boosted
then external transistor Q1 is connected to the output terminal.
7. How power amplifiers are classified?
 Class A
 Class B
 Class C
 Class AB
8. State the applications of IC LM 380
 Audio Amplifier
 High gain audio amplifier
 Phono amplifier
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 Intercom system 19
 In Sirens or alarms
9. Why current boosting is done in IC 723?
The IC 723 general purpose regulator can deliver maximum output current of
150mA.For supplying the load which demands the current more than 150 mA, the
current boosting is done in IC723.
10. Name the various protection circuits used for voltage regulators.
 Constant Current limiting
 Fold back current limiting
 Over voltage protection
 Thermal protection
11. What are the two types of regulators?
 Series Regulator in which the active element like transistor is connected in
series with the load.
 Shunt regulator in which the active element like transistor is connected in
shunt with the load.
A video amplifier has to amplify signals over a wideband of frequencies, say upto 20MHz.
It is a RCcoupled amplifier with bandwidth from d.c. to high frequency upto few
megahertz.

What is opto coupler?

An opto-isolator, also called an optocoupler, photocoupler, or optical isolator, is "an
electronicdevice designed to transfer electrical signals by utilizing light waves to providecoupling
withelectrical isolation between its input and output". The main purpose of an opto-isolator is "to
preventhigh voltages or rapidly changing voltages on one side of the circuit from damaging
components or distorting transmissions on the other side
Mention the advantages of opto-couplers:
Better isolation between the two stages.Impedance problem between the stages iseliminated.Wide
frequency response.Easily interfaced with digital circuit.Compact and light weight.Problems such
as noise, transients, contact bounce, are eliminated.
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20

of six-pulse converter?
 Commutation is made simple.
 Distortion on the ac side is reduced due to the reduction in lower order
 harmonics.
 Inductance reduced in series is considerably reduced.

18. Define Displacement Factor.

The input displacement factor is defined as the cosine of the input displacement angle.
19. Define voltage ripple factor.
It is defined as the ratio of the net harmonic content of the output voltage to the average output
voltage.
20. What is mean by full converter?
A fully controlled converter uses thyristors only and there is a wider control over the level of dc
output voltage. It is also known as two quadrant converter.
21. What are the performance factors of line commutated converters?
Input displacement angle, input power factor, DC voltage ratio, Input harmonic factor, Voltage &
current ripple factor.
22. What are the two configuration of single phase 2 pulse controlled rectifier?
 Midpoint converter
 Bridge Converter
23. What is meant by 2 pulse converter?
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Two pulse converters is defined as two triggering pulses or two sets of triggering pulses are to 21
be
generated during every cycle of the supply to trigger the various SCRs.
24. What is meant by rectification mode in single phase fully controlled converter?

In single phase full converter ∝ < 90 the voltage at the dc terminal is positive. Therefore, power
flows from source to load & the converter operates as a rectifier. Source voltage is Vs & Current is
positive. This is known as rectification mode.
25. What is meant by inversion mode? [April/May 2012,Nov/Dec 2012]

In single phase full converter ∝ > 90 the voltage at the dc terminal is negative. Therefore, power
flows from load to source & the converter operates as line commutated inverter. Source voltage Vs
is negative & Current is positive. This is known as inversion mode or synchronous mode.
26. What is the difference between half controlled & fully controlled bridge rectifier?
Half Controlled Bridge Rectifier
 Power circuit consists of mixture of diodes & SCRs
 It is one quadrant Converter
 The Dc output voltage has limited control level.

Full Controlled Bridge Rectifier

 Power circuit consists of SCRs only
 It is 2 quadrant Converter
 The Dc output voltage has wider control level

PART – B

1. Describe the effect of source inductance on the performance of a single phase full converter
indicating clearly the conduction of various thyristors during one cycle. Derive the expression for
its output voltage. May/June 2013 & May/June 2011, May/June 2014
2. Explain the principle of operation of single phase dual converter with neat power circuit
diagram. May/June 2013& May/June 2011, (April/May 2015) (Nov/Dec 2014) May/June 2014
3. Explain the working of a three phase full converter with ‘R’ load for the firing angles of 60°,
90° and 150°. Nov/Dec 2011
4. Explain the operation of a single phase full bridge converter with RL load for continuous and
discontinuous load currents. (10) Nov/Dec 2011, (April/May 2015)
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5. A single phase full bridge converter is connected to ‘R’ load. The source voltage is of 230 V, 22
50
Hz. The average load current is of 10 A. For R = 20  find the firing angle.
(6) Nov/Dec 20116. Describe the operation of a single phase two pulse bridge converter using 4
SCR'S with
relevant waveforms. (10) Nov/Dec 2010
7. Discuss the working of above converter in the converter mode with RLE load. (6) Nov/Dec
2010
8. A single phase semi converter is operated from 120 V 50 Hz ac supply. The load current with an
average value Idc is continuous and ripple free firing angle α =π/ 6 . Determine. Nov/Dec 2010
i. Displacement factor
ii. Harmonic factor of input current
iii. Input power factor.
9. Explain the operation of single phase half controlled rectifier with inductive load. Also derive an
expression for the average output voltage.
10. Explain the operation of 3 phase half controlled converter with neat waveforms. also derive an
expression for the average output voltage Nov/Dec 2012

11.A two pulse single phase bridge converter is connected to RLE load. Source voltage is 230 V,
50 HZ. Average load current .of 10 Amps is continuous over the working range. For R =0.4  and
L =2 mH compute.
(i)Firing angle delay for E =120 V.
(ii)Firing angle delay for E = -120 V.
Indicate which source is delivering power to load in parts (i) and (ii).
12. A 220v, 1kw R load is supplied by 220v,50Hz source through 1ф fully controlled converter.
Determine the following for 800w output. A) average output voltage b) rms value of i/p current c)
fundamental component of input current d) displacement factor. Nov/Dec 2012 13 A half
controlled 3 phase bridge rectifier is supplied at 220v from a source of reactance 0.24/phase.
Neglecting resistance and device volt drops determine mean load voltage for level load current of
40A at a firing delay angle of 45º and 90º.
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23

Unit 3 – UNCONTROLLED RECTIFIERS

PART – A
1. What is meant by dc chopper? [May/June 2012]
A dc chopper is a high speed static switch used to obtain variable dc voltage from a constant dc
voltage.
2. What are the applications of dc chopper? (Nov/Dec 2014)
 Battery operated vehicles
 Traction motor control in electric traction
 Trolley cars
 Marine hoists
 Mine haulers
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 Electric braking. 24
3. What are the advantages of dc chopper?
 Chopper provides
 High efficiency
 Smooth acceleration
 Fast dynamic response
 Regeneration
4. What is meant by step-up and step-down chopper?
In a step- down chopper or Buck converter, the average output voltage is less than
the input voltage. In a step- up chopper or Boost converter, the average output voltage is more than
the input voltage.
5. What is meant by duty-cycle? [May/June 2012]
Duty cycle is defined as the ratio of the on time of the chopper to the total time period of the
chopper. It is denoted by α.
6. What are the two types of control strategies? [May/June 2013]
 Time Ratio Control (TRC)
 Current Limit Control method (CLC)

7. What is meant by TRC? (April/May 2015)

In TRC, the value of Ton / T is varied in order to change the average output voltage.
8. What are the two types of TRC?
 Constant frequency control
 Variable frequency control
9. What is meant by FM control in a dc chopper?
In frequency modulation control, the chopping frequency f (or the chopping period T) is varied.
Here two controls are possible. On-time Ton is kept constant Off period Toff is kept constant.
10. What is meant by PWM control in dc chopper?
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In this control method, the on time Ton is varied but chopping frequency is kept constant. The
25
width of the pulse is varied and hence this type of control is known as Pulse Width
Modulation (PWM).
11. Write down the expression for the average output voltage for step down and step up
chopper.
Average output voltage for step down chopper is VO = α VS. Average output voltage for step up
chopper is VO = α VS x [1/ ( 1- α )].
12. What are the different types of chopper with respect to commutation process?
Voltage commutated chopper.
Current commutated chopper.
Load commutated chopper.
13. What is meant by voltage commutation?
In this process, a charged capacitor momentarily reverse biases the conducting Thyristor and turn it
off.
14. What is meant by current commutation?
In this process, a current pulse is made to flow in the reverse direction through the conducting
thyristor and when the net thyristor current becomes zero, it is turned off
15. What is meant by load commutation?
In this process, the load current flowing through the thyristor either becomes zero or is transferred
to another device from the conducting thyristor.

16. What are the advantages of load commutated chopper?

 Commutating inductor is not required.
 It is capable of commutating any amount of load current.
 It can work at high frequencies in the order of kHz.
 Filtering requirements are minimal.
17. What are the disadvantages of load commutated chopper?
a) For high power applications, efficiency becomes very low because of high switching losses at
high operating frequencies.
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b) Freewheeling diode is subjected to twice the supply voltage. 26
c) Peak load voltage is equal to twice the supply voltage.
d) The commutating capacitor has to carry full load current at a frequency of half chopping
frequency.
18. How is the inverter circuit classified based on commutation circuitry?
 Line commutated inverters. Load commutated inverters.
 Self commutated inverters.
 Forced commutated inverters.
19. What are the disadvantages of FM control?
  The chopping frequency has to be varied over a wide range for the control of output
voltage
  It generate harmonics at unpredictable frequencies
20. Differentiate between constant frequency & variable frequency control [Nov 2012]
Strategies of varying the duty cycle of DC chopper.
Constant frequency control – Frequency of the chopper remains constant , but ON period is
changed to vary the output.
Variable frequency control - Either Ton or Toff is kept constant & frequency is varied to change
the output.
21. Brief up the working of four quadrant Dc chopper.[ Nov/Dec 2012]
Output voltage and current either positive and negative so this four quadrant operation of the
chopper.

22. Define current limit control in DC–DC converter? (April/May 2015)

In this method, current is allowed to fluctuate or change only between 2 values i.e. maximum
current (I max) and minimum current (I min). When the current is at minimum value, the chopper
is switched ON. After this instance, the current starts increasing, and when it reaches up to
maximum value, the chopper is switched off allowing the current to fall back to minimum value.
This cycle continues again and again.
23. Distinguish between time ratio control and current limit control? (Nov/Dec 2014)
In TRC, the time period is kept constant, but the ‘On Time’ or the ‘OFF Time’ is varied. Using
this, the duty cycle ratio can be varied. Since the ON time or the ‘pulse width’ is getting changed
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in this method, so it is popularly known as Pulse width modulation.In TRC, the ‘TimePeriod’27 is
varied while keeping either of ‘On Time’ or ‘OFF time’ as constant. In this method, since
the time period gets changed, so the frequency also changes accordingly, so this method is
known as frequency modulation control. In CLC, current is allowed to fluctuate or change only
between 2 values i.e. maximum current (I max) and minimum current (I min). When the current is
at minimum value, the chopper is switched ON. After this instance, the current starts increasing,
and when it reaches up to maximum value, the chopper is switched off allowing the current to fall
back to minimum value. This cycle continues again and again.
24. What are the advantage and disadvantage of CUK converter? May/June 2014
1. Continuous input current
2. Continuous output current
3. Output voltage either greater than or lesser than input voltage
4. Peak to peak ripples are less

PART – B

1. A step-up chopper has input voltage of 220 V and output voltage of 660 V. If the non
conducting time of thyristor chopper is 100 µs, compute the pulse width of output voltage. Incase
pulse width is halved for constant frequency operation, find the new output voltage.(16) May/June
2011
2. Explain the various modes of operation of Boost DC-DC converter with necessary waveforms.
(16) May/June 2011& Nov/Dec 2012
3. Explain the working of Buck–Boost converter with sketch and waveforms and also drive the
expression for IS Nov/Dec 2011, (April/May 2015)

4. Discuss the principle of operation of DC-DC step up chopper with suitable waveform. Derive an
expression for its average DC output voltage. (8) May/June 2013, (April/May 2015) (Nov/Dec
2014)
5. With a neat sketch and output voltage waveforms, explain the working of full bridge SMPS.
May/June 2013 & Nov/Dec 2011
6. Discuss the principle of operation of DC-DC step down chopper with suitable waveform. Derive
an expression for its average DC output voltage. (8) Nov/Dec 2010.7. A step-down dc chopper
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hasa resistive load of R = 15 and input voltage Edc = 200 V. When the chopper remains ON, 28
its
voltage drop is 2.5 for a duty cycle of 0.5. Calculate : Nov/Dec 2010
(1) Average and r.m.s value of output voltage
(2) Power delivered to the load. (8)
8. Draw the circuit of CUK regulator and explain its working principle with necessary waveform
in detail. Nov/Dec 2010 May/June 2014
9. Classify the basic topologies of switching regulators and explain the operation of buck
regulators with continuous load current using suitable waveforms
10. Draw the circuit of buck regulator and explain its working principle with necessary waveforms.
Derive the expression for peak to peak ripple voltage of the capacitor that is present across the
load. (16) May/June 2013

Unit 4 – CONTROLLED RECTIFIERS

PART – A

1. What is meant by commutation?

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It is the process of changing the direction of current flow in a particular path of the circuit. This
29
process is used in thyristors for turning it off.
2. What are the types of commutation?
 Natural commutation
 Forced commutation
3. What is meant by natural commutation?
Here the current flowing through the thyristors goes through a natural zero and enable the
thyristors to turn off.
4. What is meant by forced commutation?
In this commutation, the current flowing through the thyristors is forced to become zeroby
external circuitry.
5. What is meant by inverter?
A device that converts dc power into ac power at desired output voltage and frequency is called an
inverter.
6. What are the applications of an inverter?
 Adjustable speed drives
 Induction heating
 Stand-by aircraft power supplies
 UPS
 HVDC transmission
7. What is the main classification of inverter?
 Voltage Source Inverter
 Current Source Inverter

8. Why thyristors are not preferred for inverters?

Thyristors require extra commutation circuits for turn off which results in decreased complexity of
the circuit. For these reasons thyristors are not preferred for inverters.
9. How output frequency is varied in case of a thyristor?
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The output frequency is varied by varying the turn off time of the thyristors in the inverter circuit,
30
i.e. the delay angle of the thyristors is varied.
13. What are the merits and demerits of CSI? [Apr/May 2011]
Merits:
 CSI does not require any feedback diodes.
 Commutation circuit is simple as it involves only thyristors.
Demerits:
 The amplitude of output current does not depend on the load
 The magnitude of the output voltage and its waveform depends upon nature of the
load impedance.
11. What is the main drawback of a single phase half bridge inverter?
It requires a 3-wire dc supply.

12. Why diodes should be connected in ant parallel with the thyristors in inverter circuits?
For RL loads, load current will not be in phase with load voltage and the diodes connected
in ant parallel will allow the current to flow when the main thyristors are turned off. Thesediodes
are called feedback diodes.
13. What types of inverters require feedback diodes?
VSI with RL load.
14. What is meant a series inverter?
An inverter in which the commutating elements are connected in series with the load is called a
series inverter.
15. Define the term inverter gain. [May/June 2012]
It is defined as the ratio of the AC output voltage to DC input voltage.

16. What is meant a parallel inverter?

An inverter in which the commutating elements are connected in parallel with the load is called a
parallel inverter.
17. What are the applications of a series inverter?
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The thyristorised series inverter produces an approximately sinusoidal waveform at a high output
31
frequency, ranging from 200 Hz to 100kHz. It is commonly used for fixed output
applications such as
 Ultrasonic generator.
 Induction heating.
 Sonar Transmitter
 Fluorescent lighting.
18. How is the inverter circuit classified based on commutation circuitry?
 Line commutated inverters.
 Load commutated inverters.
 Self commutated inverters.
 Forced commutated inverters.
19. What is meant by McMurray inverter?
It is an impulse-commutated inverter, which relies on LC circuit and an auxiliary thyristor
for commutation in the load circuit.
20. What are the applications of a CSI?
 Induction heating Lagging VAR compensation
 Speed control of ac motors
 Synchronous motor starting.
21. What is meant by PWM control?
In this method, a fixed dc input voltage is given to the inverter and a controlled ac output
voltage is obtained by adjusting the on and off periods of the inverter components. This is the most
popular method of controlling the output voltage and this method is termed as PWM control.

22. What are the advantages of PWM control? [Nov/Dec 2012] May/June 2014
The output voltage can be obtained without any additional components. Lower order
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harmonics can be eliminated or minimized along with its output voltage control. As the 32
higherorder harmonics can be filtered easily, the filtering requirements are minimized.
23. What are the disadvantages of the harmonics present in the inverter system?
Harmonic currents will lead to excessive heating in the induction motors. This will reduce the load
carrying capacity of the motor. If the control and the regulating circuits are not properly shielded,
harmonics from power ride can affect their operation and malfunctioning can result.

PART – B

1. With a neat sketch and output voltage waveforms, explain the working of three phase bridge
inverter in 180 degree mode of operation. (16) Nov/Dec 2011, (April/May 2015) (Nov/Dec
2014)
2. Discuss the different modes of operation of series resonant inverter with unidirectional switch
with neat circuit diagram and waveforms. (16) Nov/Dec 2011 May/June 2014
3. Describe the working of a 1-φ pull bridge inverter with relevant circuit and waveforms. (8)
Nov/Dec 2010
4. What is PWM? List the various PWM techniques and explain any one of them. (8) Nov/Dec
2010,Nov/Dec 2014
5. Explain the Harmonic reduction by transformer corner lines and stepped wave inverters.
Nov/Dec 2010
6. Describe the operation of single phase auto sequential commutated current source inverter
with power circuit and waveforms. (16) May/June 2011
7. Describe the operation of three phase voltage source inverter with 120° mode of operation.
(16) May/June 2013 ,Nov/Dec 2012& May/June 2011 May/June 2014
8. Explain the following PWM techniques used in inverter. May/June 2013 & Nov/Dec 2012
a. Sinusoidal PWM (8)
b. Multiple PWM. (8) (April/May 2015) May/June 2014
9. Discuss the working of a single phase series resonant inverter with appropriate circuit and
waveforms. (8)
10. (ii) With a neat circuit and relevant waveforms discuss the operation of an ideal single phase
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CSI. (8)2 Marks And 16 Marks- Question Bank 33

Unit 5 – AC PHASE CONTROLLER

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PART – A 34
1. What is Integral cycle or ON-OFF control? [Nov/Dec 2011 & May/June 2012] (Nov/Dec
2014)
ON-OFF control: In this method, the thyristors are employed as switches to connect the load
circuit to the source for a few cycles of the load voltage and disconnect it for another few cycles.
2. What is the advantage of ON-OFF control?
Due to zero-voltage and zero current switching of thyristors, the harmonics generated by the
switching action are reduced.
3. What is the disadvantage of ON-OFF control?
This type of control is applicable in systems that have high mechanical inertia and high thermal
time constant.
4. What is the duty cycle in ON-OFF control method? (April/May 2015)
Duty cycle K = n/ (n + m), where n = no. of ON cycles, m = no. of OFF cycles.
5. What is meant by unidirectional or half-wave ac voltage controller?
Here the power flow is controlled only during the positive half-cycle of the input voltage.
6. What are the types of ac voltage controller? [May/June 2013]
 1ф Uni directional or half wave ac voltage controller
 1ф Bidirectional or full wave ac voltage controller
 3ф half wave ac voltage controller
 3ф full wave ac voltage controller
7. What is meant by bidirectional or half-wave ac voltage controller?
Here the power flow is controlled during both cycles of the input voltage.
8. What is the control range of firing angle in ac voltage controller with RL load?
May/June 2014
The control range is F < a <180°, where F = load power factor angle.
9. Write the output rms voltage for 1ф ac voltage controller with R load? [Nov/Dec 2010]

10. What are the disadvantages of continuous gating signal?

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a. More heating of the SCR gate. 35
b. Increases the size of pulse transformer.
11. What is meant by high frequency carriergating?
Thyristor is turned on by using a train of pulses from a to p. This type of signal is called as high
frequency carrier gating.
12. What is meant by sequence control of ac voltage regulators?
It means that the stages of voltage controllers in parallel triggered in a proper sequence one after
the other so as to obtain a variable output with low harmonic content.
13. What are the advantages of sequence control of ac voltage regulators?
a. System power factor is improved.
b. Harmonics are reduced in the source current and the load voltage.
14. What is meant by cyclo-converter? [Nov/Dec 2010, Nov/Dec 2012& May/June
2012](Nov/Dec 2014)
It converts input power at one frequency to output power at another frequency with onestage
conversion. Cycloconverter is also known as frequency changer.
15. What are the two types of cyclo-converters? [May/June 2011]
a. Step-up cyclo-converters
b. Step-down cyclo-converters
16. What is meant by step-up cyclo-converters?
In these converters, the output frequency is less than the supply frequency.
17. What is meant by step-down cyclo-converters?
In these converters, the output frequency is more than the supply frequency.
18. What are the applications of cyclo-converter? [Nov/Dec 2011]
 Induction heating
 Speed control of high power ac drives
 Static VAR generation
 Power supply in aircraft or ship boards
19. What is meant by positive converter group in a cyclo converter?
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The part of the cycloconverter circuit that permits the flow of current during Positive half cycle36
of
output current is called positive converter group.
20. What is meant by negative converter group in a cyclo converter?
The part of the cyclo converter circuit that permits the flow of current during negative half
cycle of output current is called negative converter group.
21. What does ac voltage controller mean?
It is device, which converts fixed alternating voltage into a variable voltage without change
in frequency.
22. What are the applications of phase controlled converter or ac voltage controllers?
[Nov/Dec 2012 & 2010]
 Domestic and industrial heating
 Lighting control
 Speed control of single phase and three phase ac motors
 Transformer tap changing
24. What are the advantages of ac voltage controllers?
 High efficiency
 Flexibility in control
 Less maintenance
25. What are the disadvantages of ac voltage controllers?
The main draw back is the introduction of harmonics in the supply current and the load voltage
waveforms particularly at low output voltages.
26. What are the two methods of control in ac voltage controllers?
 ON-OFF control
 Phase control
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37
PART – B

1. Explain the principle of integral cycle. May/June 2013

2. Explain the operation of multistage control of AC voltage controllers with neat diagram.
May/June 2013& May/June 2011
3. .Explain the operation of 1- φ AC voltage controller with RL load. (April/May 2015)
4. Explain the 2 stage sequence control of AC voltage controller. Nov/Dec 20115. Explain the
operation of 1ф to 1ф step down cyclo converter with power circuit and waveforms.
May/June 2011, (April/May 2015)
6. A 1- φ sinusoidal AC voltage controller has input voltage 230v, 50Hz and a load of R=15Ώ. For
6 cycles ON and 4 cycles OFF determine. i) rms output voltage ii) input PF iii) avg & rms thyristor
currents. May/June 2013
7. Describe the operation of single phase ac voltage controller with the help of voltage and current
waveform. Also derive the expression for average value of the output voltage. Nov/Dec 2010
8. Describe 3ф to 3ф cycloconverter with relevant circuit arrangement using 18 thyristors. (8)
Nov/Dec 2010 & Nov/Dec 2011