# MCQ in Power Electronics Part 3 | ECE Board Exam

(Last Updated On: August 10, 2022) This is the Multiple Choice Questions Part 3 of the Series in Power Electronics as one of the Electronics Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electronics Engineering field, Electronics Books, Journals and other Electronics References.

#### Continue Practice Exam Test Questions Part 3 of the Series

Choose the letter of the best answer in each questions.

101. Which device can be used in a chopper circuit?

A. BJT

B. MOSFET

C. GTO

D. All of the mentioned

Solution:

102. A chopper is a

A. Time ratio controller

B. AC to DC converter

C. DC transformer

D. High speed semiconductor switch

Solution:

103. What is the duty cycle of a chopper?

A. Ton/Toff

B. Ton/T

C. T/Ton

D. Toff x Ton

Solution:

104. The load voltage of a chopper can be controlled by varying the

A. duty cycle

B. firing angle

C. reactor position

D. extinction angle

Solution:

105. The values of duty cycle (α) lies between

A. 0<α<1

B. 0>α>-1

C. 0<=α<=1

D. 1<α<100

Solution:

106. If T is the time period for a chopper circuit and α is its duty cycle, then the chopping frequency is

A. Ton

B. Toff

C. α/Toff

D. α/Ton

Solution:

107. AC voltage controllers convert

A. Fixed ac to fixed dc

B. Variable ac to variable dc

C. Fixed ac to variable ac

D. Variable ac to fixed ac

Solution:

108. In AC voltage controllers the

A. variable ac with fixed frequency is obtained

B. variable ac with variable frequency is obtained

C. variable dc with fixed frequency is obtained

D. variable dc with variable frequency is obtained

Solution:

109. The GTO (gate turn-off thyristor) is a

A. p-n-p-n device

B. p-n-p device

C. p-metal-n device

D. p-n single junction device

Solution:

110. The GTO can be turned off

A. by a positive gate pulse

B. by a negative gate pulse

C. by a negative anode-cathode voltage

D. by removing the gate pulse

Solution:

111. In GTO The anode current is ideally limited by the

A. gate pulse amplitude

B. internal impedance of the device

D. gate circuit impedance

Solution:

112. In a GTO the n+ layer forms the

A. anode & gate

B. cathode & gate

C. cathode

D. gate

Solution:

113. The turn-off gain βoff of the GTO is given by

A. Ig/Ia

B. Ia/Ig

C. Vg/Va

D. Vg/Va

Solution:

114. A GTO can be represented by two transistors T1 & T2. The current gain of both transistors are α1 and α2 respectively. A low value of gate current requires

A. low value of α1 and α2

B. low value of α1 and high value of α2

C. high value of α1 and low value of α2

D. high values of α1 and α2

Solution:

115. Gold doped GTOs have _________ as compared to the conventional GTOs

A. high turn-off time

B. low negative gate current requirement

C. low reverse voltage blocking capabilities

D. lower positive gate current requirement

Solution:

116. Latching current for the GTOs is ______ as compared to CTs (Conventional thyristors).

A. more

B. less

C. constant

D. cannot be said

Solution:

117. In case of the two-transistor model (T1 & T2) of GTO with anode-short, the anode-short is placed between the

A. emitter of T1 & T2

B. emitter of T1 & base of T2

C. emitter of T1 & base of T1

D. emitter of T1 & collector of T2

Solution:

118. Choose the correct statement: GTOs have _________ as compared to the CTs.

A. less on-state voltage drop

B. less gate drive losses

C. higher reverse blocking capabilities

D. faster switching speed

Solution:

119. A single-phase voltage controller, using one SCR in anti-parallel with a diode, feeds a load R and Vs = 230 V. For a firing angel of 90° for the SCR, the PMMC voltage connected across R would read

A. 0

B. 51.8 V

C. –51.8 V

D. –36.82 V

Solution:

120. A single phase voltage controller has input of 230 V and a load of 15 Ω resistive. For 6 cycles on and 4 cycles off, determine the average value of SCR current.

A. 21.68 A

B. 200 mA

C. 4.14 A

D. 2.07 A

Solution:

121. An IGBT has three terminals called:

A. Collector, Emitter and Base

B. Drain, Source and Base

C. Drain, Source and Gate

D. Collector, Emitter and Gate

Solution:

122. The function of snubber circuit connected across the SCR is to:

A. Suppress dv/dt

B. Increase dv/dt

C. Decrease dv/dt

D. Decrease di/dt

Solution:

123. An UJT exhibits negative resistance region:

A. Before the break point

B. Between peak and valley point

C. After the valley point

D. Both (a) and (c)

Solution:

124. For dynamic equalizing circuit used for series connected SCRs, the choice of C is based on:

A. Reverse recovery characteristics

B. Turn-on characteristics

C. Turn-off characteristics

D. Rise time characteristics

Solution:

125. A four quadrant operation require:

A. Two full converters in series

B. Two full converters connected back-to-back

C. Two full converters connected in parallel

D. Two semiconductors connected back-to-back

Solution:

126. In a circulating-current type of dual converter, the nature of the voltage across the reactor is:

A. Alternating

B. Pulsating

C. Direct

D. Triangular

Solution:

127. The frequency of the ripple in the output voltage of 3-phase semiconductor depends on:

A. Firing angle and load resistance

B. Firing angle and load inductance

D. Firing angle and the supply frequency

Solution:

128. A single-phase full bridge inverter can operate in load-commutation mode in case load consists of:

B. RLC underdamped

C. RLC damped

D. RLC critically damped

Solution:

129. Practical way of obtaining static voltage equalization in series connected SCRs is by the use of:

A. One resistor across the string

B. Resistors of different values across each SCR

C. Resistors of the same value across each SCR

D. One resistor in series with each SCR

Solution:

130. A resistor connected across the gate and cathode of an SCR in a circuit increases its

A. dv/dt rating

B. Holding current

C. Noise Immunity

D. Turn-off time

Solution:

131. In thyristor, holding current is:

A. more than the latching current

B. less than the latching current

C. equal to latching current

D. none of the above

Solution:

132. When a thyristor turn on, the gate drive:

A. can be turned down but thyristor remains in on position

B. cannot be turned down as thyristor will be turned off

C. gate drive has no impact on starting and turning off the thyristor

D. none of the above

Solution:

133. A thyristor can be termed as:

A. DC switch

B. AC switch

C. both AC and DC switch

D. none of the above

Solution:

134. During forward blocking state, a thyristor is associated with:

A. large current and low voltage

B. low current and large voltage

C. medium current and large voltage

D. None of the above

Solution:

135. Turn-off time of an SCR is measured from the instant:

A. anode current becomes zero

B. anode voltage becomes zero

C. anode voltage and anode current becomes zero

D. gate current becomes zero

Solution:

136. A forward voltage can be applied to an SCR after its:

A. anode current reduces to zero

B. gate recovery time

C. reverse recovery time

D. anode voltage reduces to zero

Solution:

137. In a thyristor, the magnitude of the anode current will:

A. increase if the gate current is increased

B. decrease if the gate current is decreased

C. increase if gate current is decreased

D. no change with the variation of the gate current

Solution:

138. In a thyristor, ratio of latching current to holding current is:

A. 0.4

B. 1.0

C. 2.5

D. 4.0

Solution:

139. Once SCR starts conducting a forward current, its gate losses control over:

A. anode circuit voltage only

B. anode circuit current only

C. anode circuit voltage and current

D. none of the above

Solution:

140. On state voltage drop across thyristor used in a 230 V supply system is of the order:

A. 110-115V

B. 250 V

C. 1- 1.5 V

D. none of the above

Solution:

141. Silicon controlled rectifier can be turned on

A. By applying a gate pulse and turned off only when current becomes zero

B. And turned off by applying gate pulse

C. By applying a gate pulse and turned off by removing the gate pulse

D. By making current nonzero and turned off by making current zero

Solution:

142. TRIAC is a semiconductor power electronic device which contains

A. Two SCRs connected in reverse parallel

B. Two SCRs connected in parallel

C. Two SCRs connected in series

D. Two BJT’s connected in series

Solution:

143. An SCR can be used

A. as static conductor

B. for power control

C. for speed control of dc shunt motor

D. all of these

Solution:

144. A crowbar is a circuit which is used to protect a

A. voltage sensitive load from excessive dc power supply output voltages

B. current sensitive load from excessive dc power supply output voltages

C. voltage sensitive load from excessive ac power supply output voltages

D. current sensitive load from excessive ac power supply output voltages

Solution:

145. The input current waveform of a bridge-controlled rectifier when the load is perfectly filtered is

A. Sine wave

B. Square wave

C. Saw – tooth wave

D. Trapezoidal wave

Solution:

146. The advantage of using free – wheeling diode in half controlled bridge converter is that

A. There is always a path for the dc current independent of the ac line

B. There is always a path for the ac current independent of the ac line

C. There is always a path for the dc current dependent of the ac line

D. There is always a path for the ac current independent of the ac line

Solution:

147. Harmonics in 3 phase inverters can be reduced by using

A. Passive filter

B. Active filter

C. Both passive and active filters

D. None of these

Solution:

148. The most suited gate pulses given to the AC regulator with R – L load can be in the form of

A. Continuous signal

B. Large isolating pulse transformer

C. A train of pulses

D. None of these

Solution:

149. With increase in firing angle,

A. Both harmonic distortion and quality of input current increases

B. Harmonic distortion increases and quality of input current decreases

C. Harmonic distortion decreases and quality of input current increases

D. Both harmonic distortion and quality of input current decreases

Solution:

150. The power MOSFET device is a

A. Current controlled unipolar device

B. Voltage controlled unipolar device

C. Current controlled bipolar device

D. Voltage controlled bipolar device

Solution:

### Complete List of MCQ in Electronics Engineering per topic

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