power electronics Mcqs
151. Practical way of obtaining static voltage equalization in series connected SCRs is by the use of____________?
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A. Resistors of the same value across each SCR

B. One resistor across the string

C. Resistors of different values across each SCR

D. One resistor in series with each SCR

153. Anode current in an SCR consists of____________?
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A. holes only

B. electrons only

C. either electron or holes

D. Both electron and holes

154. In a 3 phase bridge rectifier the ripple frequency is _____________?
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A. Twice the input frequency

B. Three times the input frequency

C. Six times the input frequency

D. Equal to the input frequency

155. Leakage current flows through the thyristor in_________?
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A. forward blocking mode

B. reverse blocking mode

C. both forward and reverse blocking mode

D. forward conduction mode

156. By which one of the following we can measure the reliability of a string_____________?
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A. Derating factor

B. Reliability factor

C. Factor of safety

D. String efficient

161. SCRs are used in series to meet_______________?
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A. low voltage demand

B. high current demand

C. low current demand

D. high voltage demand
162. Materials used in heat sink should have_____________?
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A. high melting point

B. large surface area

C. All of these

D. high thermal conductivity

163. Between the incoming and outgoing devices in voltage commutation
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A. Large overlapping takes place

B. Small overlapping operation

C. No overlapping operation

D. None of these

164. An ideal diode is___________?
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A. Unidirectional

B. Fixed voltage polarity

C. Only (a) and (c)

D. Bidirectional

165. The output current in PWM DC DC converters is equal to___________?
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A. Product of an average inductor current and a function of duty ratio

B. None of these

C. Average value of the output inductor current

D. Either A. or B.
166. During the commutation period in 3 phase converter, overlap time is____________?
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A. Dependent on the load current

B. Dependent on the voltage

C. Dependent on both the load current and load voltage behind the short circuit current

D. Independent on both the load current and load voltage

167. Single phase VSI are mainly used in___________?
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A. Multilevel configuration

B. Ups

C. Power supplies

D. All of these
168. AC power in a load can be controlled by using_____________?
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A. four SCRs in series

B. two SCRs in parallel opposition

C. three SCRs in series

D. two SCRs in series

169. In radiative coupling, the emitter radiation field_____________?
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A. Decays as 1 / R, where R is the separation distance between the emitter and the receptor

B. Decays as R, where R is the separation distance between the emitter and the receptor

C. Decays as 1 / 2 R, where R is the separation distance between the emitter and the receptor

D. Decays as 2R, where R is the separation distance between the emitter and the receptor

170. BCT is used for____________?
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A. Low power phase control

B. Low power current control

C. High power phase control

D. High power current control

171. Double edge modulation eliminates certain harmonics when the reference is a__________?
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A. Sine wave

B. Square wave

C. Trapezoidal wave

D. Triangular wave

172. Spread time is defined as the interval during which_____________?
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A. anode voltage drops from 10 % of its initial value to zero

B. anode current rises from 90 % to its final value

C. both (A) and (B)

D. anode current rises from 10 % to 90 % of its final value

173. After proper turn on of thyristor____________?
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A. gate signal should present but can be removed

B. none of the above.

C. gate signal must be removed

D. gate signal is always present

175. An SCR is made up of silicon because_____________?
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A. silicon has small leakage voltage than germanium

B. silicon has small leakage current than germanium

C. silicon has large leakage voltage than germanium

D. silicon has large leakage current than germanium

176. IGBT stands for___________?
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A. Inductive gate bidirectional transistor

B. Insulated gate bipolar transistor

C. Inductive gate bipolar transistor

D. Insulated gate bidirectional transistor

177. A Triac has three terminals viz ___________?
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A. Drain, source, gate

B. Two main terminal and a gate terminal

C. Cathode, anode, gate

D. None of the above

179. In a silicon controlled rectifier, the load is connected___________?
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A. Across cathode

B. In series with anode

C. In series with cathode

D. Across anode

180. MOSFET stands for______________?
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A. Metal oxide semiconductor field effect transistor

B. Molybdenum oxide semiconductor field effect transistor

C. Metal oxide semiconductor field effect transmitter

D. Metal oxide silicon field effect transistor

182. Gate circuit or triggering circuit of a thyristor is
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A. high power circuit.

B. may be low power or high power circuit

C. lower power circuit.

D. magnetic circuit.

183. SCR will be turned off when anode current is_______________?
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A. < latching current but greater than holding current and gate signal is 0.

B. less than holding current.

C. < latching current but greater than holding current and gate signal is present.

D. both (A) and (B).
185. In current commutated DC-DC choppers, the voltage spike appears across the load when_____________?
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A. Voltage across the commutating inductances collapses

B. The capacitance voltage adds to the supply voltage

C. Both A. and B.

D. None of these

186. In a lossless inverter, the average power absorbed in one period by the load must be__________?
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A. Equal to the average power supplied by the dc source

B. Greater than the average power supplied by the dc source

C. Equal to the average power supplied by the ac source

D. Lesser than the average power supplied by the dc source

187. The latching current of GTO should be of order
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A. 100 mA

B. 500 mA

C. 1:00 AM

D. 2:00 AM

189. With increase in firing angle,
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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

190. Which statement is true for latching current ___________?
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A. t is related to turn off process of the device.

B. It is related to conduction process of device.

C. It is related to turn on process of the device.

D. Both C and D.

192. During the commutation period in 3 phase converter, overlap time is_____________?
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A. Dependent on the load current

B. Dependent on the voltage

C. Dependent on both the load current and load voltage behind the short circuit current

D. Independent on both the load current and load voltage

196. What may happen high dV / dt____________?
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A. Unwanted turn ON

B. Breakdown of J2 junction

C. Both A and B

D. Anyone of these

197. What is used to protect a thyristor from high di / dt conditions__________?
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A. Inductor

B. Fuse.

C. Voltage clamping device

D. Snubber circuit

198. Regulator sampling PWM is usually used in___________?
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A. High power inverters

B. Rectifiers

C. Low power inverters

D. Only A. and B.
200. The maximum di/dt in a SCR is____________?
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A. Directly proportional to supply voltage

B. Directly proportional to inductance in the circuit

C. Inversely proportional to supply voltage

D. Both A and B