Explore topic-wise MCQs in Power Electronics.

This section includes 257 Mcqs, each offering curated multiple-choice questions to sharpen your Power Electronics knowledge and support exam preparation. Choose a topic below to get started.

1.

In given fig., zero centre and ideal PMMC voltmeters M1 and M2 will read:

A. 10 V, 10 V
B. 0, 10 V
C. 10 V, 7 07 V
D. 10V, 7 07 V
Answer» B. 0, 10 V
Discussion
2.

In given fig. capacitor C is initially charged with voltage V0 with upper plate positive. Switch S is closed at t = 0. At t = 0+, VC and i are respectively:

A.
Answer» C.
Discussion
3.

The speed and torque of induction motors can be varied by which of the following means:
1. Stator voltage control
2. Rotor voltage control
3. Frequency control

A. 1 only
B. 2 only
C. 1 and 2 only
D. 1, 2 and 3
Answer» E.
Discussion
4.

MOS controlled thyristors have:
1. Low forward voltage drop during conduction
2. Fast turn-on and turn-off time
3. Low switching losses
4. High reverse voltage blocking capability
5. Low gate input impedance
Which are correct?

A. 1, 2, 3
B. 3, 4, 5
C. 2, 3, 4
D. 1, 3, 5
Answer» B. 3, 4, 5
Discussion
5.

For a sinusoidal input voltage
Vs = Vm sin t = 2 Vs sin t
If the input voltage is connected to load for n cycles and is disconnected for m cycles, the rms output voltage is given by
V0 = Vs K
Where k is duty cycle which is given by:

A. m + n
B. m n
C. mn
D. n/(m + n)
Answer» E.
Discussion
6.

In given fig., if C = 8 F and L = 0 2 mH, the peak current handled by diode is

A. 40 A
B. 50 A
C. 10 A
D. 30 A
Answer» C. 10 A
Discussion
7.

In given fig., V1, V2 and V3 are zero centre PMMC voltmeters. The circuit is initially relaxed. Switch S is closed at t = 0. In steady state, readings of voltmeters V1, V2 and V3 are respectively:

A. 100 V, 100 V, 100 V
B. 100 V, 0, 200 V
C. 100 V, 0, 200 V
D. 100 V, 0, 100 V
Answer» D. 100 V, 0, 100 V
Discussion
8.

Consider the following statements: The overlap angle of a phase controlled converter would increase on increasing the
1. Supply voltage
2. Supply frequency
3. Load current
4. Source inductance Of these statements which are correct:

A. 1, 2, 3
B. 2, 3, 4
C. 1, 2, 4
D. 1, 3, 4
Answer» D. 1, 3, 4
Discussion
9.

For thyristor, pulse triggering is preferred to d.c. triggering because
1. Gate dissipation is low
2. Pulse system is simpler
3. Trigging signal is required for a very short duration

A. Only statement 1 is correct
B. Only statement 2 is correct
C. Statements 2 and 3 are correct
D. Statements 1, 2 and 3 are correct
Answer» E.
Discussion
10.

Consider the following statements about SCR
1. For Normal SCR, Turn-on time is more than turn off time
2. A forward voltage can be applied to an SCR after its gate recovery time
3. Static V I characteristics of an SCR with different Gate drives applied to the Gate are indicated by
Vg2 > Vg1 > Vg0

A. 1 only
B. 2 only
C. 2 and 3 only
D. 1 and 2 only
Answer» D. 1 and 2 only
Discussion
11.

Which of the following regulator can provide o/p voltage more than or less than the I/P voltage?
1. Buck regulator
2. Boost regulator
3. Buck-boost Regulator
4. Cuk regulator

A. 1 and 2 only
B. 2 and 3 only
C. 3 and 4 only
D. 1, 2 and 3 only
Answer» D. 1, 2 and 3 only
Discussion
12.

Which of the following statements are correct?
1. BJT have + Ve temperature coefficient
2. diodes are connected in series to increase the Blocking voltage capability
3. The Input power factor of controllers which varies with delay angle is generally poor, especially at the low o/p range

A. 1 and 2 only
B. 2 and 3 only
C. 1 and 3 only
D. 1, 2 and 3
Answer» C. 1 and 3 only
Discussion
13.

An ideal rectifier should have
1. Harmonics factor = 1
2. Transformer utilisation factor = 1
3. Efficiency = 100%
4. Effective value of AC component of o/p voltage = 0
5. The I/P power factor = 1
The correct statements are:

A. 1 and 2 only
B. 1, 2 and 3 only
C. 2, 3 and 4 only
D. 2, 3 and 5 only
Answer» E.
Discussion
14.

Which of the following thyristors are Gate turned OFF device?
1. Gate turned off thyristor
2. Static induction thyristor
3. MOS controlled thyristor

A. 1 only
B. 2 only
C. 1 and 2 only
D. 1, 2 and 3 only
Answer» E.
Discussion
15.

A single-phase voltage controller is connected to a load of resistance 10 and a supply of 200 sin 314 t volts. For a firing angle of 90 , the average thyristor current in amperes is

A. 10
B. 10/
C. 5
D. /
E. 5
Answer» C. 5
Discussion
16.

A load, consisting of R = 10 and L = 10 , is being fed from 230 V, 50 Hz source through a 1-phase voltage controller. For a firing angle delay of 30 , the rms value of load current would be

A. 23 A
Answer» C.
Discussion
17.

A resistor connected across the gate and cathode of an SCR increases its
(i) dv/dt rating
(ii) holding current
(iii) noise immunity
(iv) turn-off time
The correct codes is/are:

A. (i) Only
B. (i) and (ii) Only
C. (i), (ii) and (iii) Only
D. (ii) and (iv) Only
Answer» D. (ii) and (iv) Only
Discussion
18.

For a 3-phase, six-pulse diode rectifier, the average output voltage in terms of maximum value of line voltage Vm is

A. (a)
B. (b)
C. (c)
D. (d)
Answer» C. (c)
Discussion
19.

In a 3-phase semiconverter, for firing angle equal to 90 and for continuous conduction, freeweeling diode conducts for

A. 30
B. 60
C. 90
D. zero degree
Answer» B. 60
Discussion
20.

Chopper configurations
(A)Voltage-commutated chopper
(B)Load-commutated chopper
(C)Current-commutated chopper
(D)Ideal dc chopper

A. 2 4 1 3
B. 2 4 3 1
C. 4 2 1 3
D. 3 4 1 2
Answer» B. 2 4 3 1
Discussion
21.

When a series LC circuit is connected to a dc supply of V volts through a thyristor, then the peak current through thyristor is

A. V
B. V/
C. V
D. V
Answer» D. V
Discussion
22.

Types of choppers
(A) Type-A chopper
(B) Type-B chopper
(C) Type-C chopper
(D) Type-D chopper

A. 3 1 4 2
B. 2 1 4 3
C. 3 4 1 2
D. 3 1 2 4
Answer» B. 2 1 4 3
Discussion
23.

Controlled rectifiers
(A) 1-phase full converter
(B) 1-phase semiconverter
(C) 3-phase half-wave converter
(D) 3-phase semiconverter
Output voltage expressions
1.
3Vm
(1 + cos )
2

2.
2Vm
cos

3.
Vm
(1 + cos )

4.
3 3
(Vm cos )
2

A. 2 3 4 1
B. 1 3 4 2
C. 2 3 1 4
D. 2 1 4 3
Answer» B. 1 3 4 2
Discussion
24.

In a 3-phase half-wave diode rectifier, if Vm is the maximum value of per phase voltage, then each diode is subjected to a peak inverse voltage of

A. V
B.
C. V
D. 2 V
E. 3 V
Answer» C. V
Discussion
25.

For an UJT employed for the triggering of an SCR, standoff ratio = 0 64 and dc source voltage VBB is 20 V. The UJT would trigger when the emitter voltage is

A. 12 8 V
B. 13 1 V
C. 10 V
D. 5 V
Answer» C. 10 V
Discussion
26.

Whan an UJT is used for triggering an SCR, the wave shape of the voltage obtained from UJT circuit is a

A. sine wave
B. saw-tooth wave
C. trapezoidal wave
D. square wave
Answer» C. trapezoidal wave
Discussion
27.

In a GTO, anode current begins to fall when gate current

A. is negative peak at time t = 0
B. is negative peak at t = storage period t
C. just begins to become negative at t = 0
D. is negative peak at t = (t
E. + fall time)
Answer» C. just begins to become negative at t = 0
Discussion
28.

Thermal resistance in SCRs has the units of (W/ C, or ohms or C/W) and heat sinks are made from (copper/steel/aluminium)
A. C/W, Aluminium
B. C/W, Copper
C. W/ C, Aluminium
D. W/ C, Copper
Answer» B. C/W, Copper
Discussion
29.

The object of connecting resistance and capacitance across gate circuit is to protect the SCR gate against

A. over-voltages
B. dv/dt
C. noise signals
D. over-currents
Answer» D. over-currents
Discussion
30.

For an SCR, di/dt protection is achieved through the use of

A. R in series with SCR
B. RL in series with SCR
C. L in series with SCR
D. L across SCR
Answer» C. L in series with SCR
Discussion
31.

For an SCR, dv/dt protection is achieved through the use of

A. RL in series with SCR
B. RC across SCR
C. L in series with SCR
D. RC in series with SCR
Answer» C. L in series with SCR
Discussion
32.

Turn-on time of an SCR in series with RL circuit can be reduced by

A. increasing circuit resistance
B. decreasing
C. increasing circuit inductance
D. decreasing
Answer» E.
Discussion
33.

Consider the following statements regarding speed control of induction motors by means of external rotor resisters:
1. Reduction in speed is accompanied by reduced efficiency
2. With a large resistance in the rotor circuit, the speed would vary considerably with variation in torque.
3. The method is very complicated. The disadvantage of such a method of speed control would include:

A. 1 and 3
B. 2 and 3
C. 1 and 2
D. 1, 2 and 3
Answer» B. 2 and 3
Discussion
34.

Consider the following statements: The Diode in a voltage source inverter (Mc Murry inverter) should be able to
1. Withstand a large voltage in the reverse direction
2. Carry the commutating current excess of load current
3. Provide the required reverse bias to the outgoing thyristor.
4. Feedback the reactive current to the source of these statements

A. 1, 2 and 3 are correct
B. 1, 3 and 4 are correct
C. 2, 3 and 4 are correct
D. 1, 2 and 4 are correct
Answer» D. 1, 2 and 4 are correct
Discussion
35.

In Fig. ideal moving iron voltmeters M1 and M2 will respectively read

A. 141 4 V, 141 4 V
B. 0, 141 4 V
C. 0, 200 V
D. 141 4 V, 0
Answer» C. 0, 200 V
Discussion
36.

In the circuit of given Fig. the diode states at the extremely large negative value of the input voltage vi are

A. D1 off, D2 off
B. D1 on, D2 off
C. D1 off, D2 on
D. D1 on, D2 on
Answer» C. D1 off, D2 on
Discussion
37.

For a symmetrical square wave of 800 V peak to peak and for ideal diode, the voltmeter in Fig. will read

A. 200 V
B. 400 V
C. 800 V
D. zero
Answer» B. 400 V
Discussion
38.

For normal SCRs, turn-on time is

A. less than turn-off time t
B. more than t
C. equal to t
D. half of t
Answer» B. more than t
Discussion
39.

In Fig. V1 and V2 are zero centre PMMC voltmeters. When a sinusoidal signal is applied, V2 reads + 20 V. The reading of the voltmeter V1 is volts.

A. 20 V
B. 20 V
C. 10 V
D. None of these
Answer» C. 10 V
Discussion
40.

In a thyristor, holding current is

A. more than latching current I
B. less than I
C. equal to I
D. very small
Answer» C. equal to I
Discussion
41.

13. In the circuit of Fig. the 5V zener diode requires a minimum current of 10 mA. For obtaining a regulated output of 5 V, the maximum permissible load current IL is and the minimum power rating of zener diode is .

A. 40 mA, 0 05 W
B. 20 mA, 0 05 W
C. 40 mA, 0 5 W
D. 20 mA, 0 5 W
Answer» B. 20 mA, 0 05 W
Discussion
42.

The circuit in Fig. shows zener-regulated dc power supply. The zener diode is ideal. The minimum value of RL down to which the output voltage remains constant is

A. 27
B. 45
C. 15
D. 24
Answer» C. 15
Discussion
43.

In Fig. zero centre and ideal PMMC voltmeters M1 and M2 will read

A. 10 V, 10 V
B. 0, 10 V
C. 10 V, 7 07 V
D. 10 V, 7 07 V
Answer» B. 0, 10 V
Discussion
44.

In a BJT

A.
B.
C.
Answer» C.
Discussion
45.

In given fig., suppose capacitor C is charged to 50V with lower plate positive. Switch S is closed at t = 0. Current through the diode at t = 0 and final voltage across C are respectively:

A. 25 A, 250 A
B. 25 A, 200 V
C. 20 A, 200 V
D. 15 A, 150 V
Answer» C. 20 A, 200 V
Discussion
46.

Analysis of voltage waveform of a single phase bridge converter shows that it contains X% of 6th harmonics. The 6th harmonic content of the voltage waveform of a 3- bridge converter would be:

A. Less than X% due to an increase in the number of pulses
B. Equal to X%, the same as that of the single phase converter
C. Greater than X% due to changes in o/p and i/p voltages of the converter
D. Difficult to predict as the analysis of converters is not governed by any generalised theory
Answer» B. Equal to X%, the same as that of the single phase converter
Discussion
47.

In resonance pulse inverters:

A. DC output voltage variation is wide
B. The frequency is low
C. The output voltage is never sinusoidal
D. DC saturation of transformer core is minimised
Answer» E.
Discussion
48.

A voltage source inverter is normally employed when:

A. Source inductance is large and load inductance is small
B. Source inductance is small and load inductance is large
C. Both source and load inductances are small
D. Both source and load inductances are large
Answer» D. Both source and load inductances are large
Discussion
49.

Use of a reverse conducting thyristor in place of antiparallel combination of thyristor and feedback diode in a inverter:

A. Effectively minimises the peak commutating current
B. Decreases the operating frequency of operation
C. Minimises the effects of load inductance on the commutation performance
D. Causes deteriorationin the commutation performance
Answer» E.
Discussion
50.

In given fig., if C = 8

A. 40 A
B. 50 A
C. 10 A
D. 30 A
Answer» C. 10 A
Discussion