131. In a 3-phase bridge inverter operating at 180° conduction, the output line voltage waveform is
A) Square wave
B) Trapezoidal
C) Sinusoidal
D) Pulsating DC
Answer: A) Square wave
132. In sinusoidal PWM, increasing the carrier frequency will
A) Reduce harmonics
B) Increase harmonics
C) Reduce output voltage
D) Increase output voltage
Answer: A) Reduce harmonics
133. The turn-on loss of an IGBT is generally
A) Less than turn-off loss
B) Equal to turn-off loss
C) Greater than turn-off loss
D) Zero
Answer: A) Less than turn-off loss
134. The function of snubber circuit across an SCR is
A) To limit di/dt
B) To limit dv/dt
C) To increase current
D) To reduce delay angle
Answer: B) To limit dv/dt
135. The most suitable commutation method for low-power SCR is
A) Class-A
B) Class-C
C) Class-E
D) Class-D
Answer: A) Class-A
136. The firing circuit of an SCR is synchronized with
A) Load current
B) Supply voltage
C) Gate current
D) Load voltage
Answer: B) Supply voltage
137. The on-state voltage drop of SCR mainly depends on
A) Anode current
B) Junction temperature
C) Gate current
D) Forward blocking voltage
Answer: B) Junction temperature
138. The di/dt protection for SCR is provided by
A) RC snubber
B) RL series circuit
C) Freewheeling diode
D) Zener diode
Answer: B) RL series circuit
139. The main disadvantage of phase-controlled rectifier is
A) High output voltage
B) Poor input power factor
C) High efficiency
D) Simple control
Answer: B) Poor input power factor
140. In 3-phase controlled rectifier, ripple frequency is
A) 3 × supply frequency
B) 6 × supply frequency
C) Equal to supply frequency
D) Twice supply frequency
Answer: B) 6 × supply frequency
141. In regenerative braking of DC motor using converter, the converter operates as
A) Inverter
B) Rectifier
C) Chopper
D) Cycloconverter
Answer: A) Inverter
142. The maximum output voltage in a single-phase half converter occurs at
A) α = 0°
B) α = 45°
C) α = 90°
D) α = 180°
Answer: A) α = 0°
143. The load current in a single-phase full converter is continuous if
A) Load is pure resistive
B) Load has high inductance
C) Firing angle is high
D) Firing angle is low
Answer: B) Load has high inductance
144. The GTO can be turned off by
A) Removing gate signal
B) Applying reverse gate current
C) Decreasing anode voltage
D) Reducing anode current
Answer: B) Applying reverse gate current
145. The output voltage of a buck converter is always
A) Greater than input
B) Less than input
C) Equal to input
D) Variable around input
Answer: B) Less than input
146. In a boost converter, the inductor current is
A) Constant
B) Always decreasing
C) Rippled
D) Zero
Answer: C) Rippled
147. The voltage stress on diode in boost converter is
A) Equal to output voltage
B) Equal to input voltage
C) Sum of input and output
D) Zero
Answer: A) Equal to output voltage
148. The PWM inverter is preferred because it
A) Reduces switching losses
B) Improves output waveform
C) Increases harmonics
D) Reduces power factor
Answer: B) Improves output waveform
149. In a 3-phase full converter, average output voltage is proportional to
A) Cos α
B) Sin α
C) α
D) tan α
Answer: A) Cos α
150. In a step-up chopper, the average output current is
A) Greater than input current
B) Less than input current
C) Equal to input current
D) Zero
Answer: B) Less than input current
151. In a chopper, the control of output voltage is done by varying
A) Supply voltage
B) Duty cycle
C) Frequency
D) Load
Answer: B) Duty cycle
152. The forced commutation is used in
A) SCR
B) BJT
C) MOSFET
D) IGBT
Answer: A) SCR
153. The voltage rating of GTO is limited due to
A) High gate current
B) Large turn-off time
C) Large junction capacitance
D) Low efficiency
Answer: B) Large turn-off time
154. The static V–I characteristics of SCR during forward blocking region resemble
A) Open switch
B) Closed switch
C) Resistor
D) Diode
Answer: A) Open switch
155. The TRIAC can conduct current in
A) One direction
B) Both directions
C) Reverse only
D) None
Answer: B) Both directions
156. The triggering of TRIAC can be done in
A) One quadrant
B) Two quadrants
C) Four quadrants
D) Three quadrants
Answer: C) Four quadrants
157. The thyristor is a
A) Unidirectional, unipolar device
B) Unidirectional, bipolar device
C) Bidirectional, unipolar device
D) Bidirectional, bipolar device
Answer: B) Unidirectional, bipolar device
158. In a current source inverter, output current is
A) Constant
B) Variable
C) Depends on load
D) Zero
Answer: A) Constant
159. The snubber circuit is used in inverter to
A) Limit switching losses
B) Limit dv/dt
C) Limit di/dt
D) Both B and C
Answer: D) Both B and C
160. The most significant advantage of IGBT over BJT is
A) Voltage-controlled device
B) High β
C) Low cost
D) High current
Answer: A) Voltage-controlled device
161. The MOSFET is
A) Current controlled
B) Voltage controlled
C) Power controlled
D) Thermal controlled
Answer: B) Voltage controlled
162. The transfer characteristic of MOSFET is
A) Linear
B) Non-linear
C) Exponential
D) Logarithmic
Answer: A) Linear
163. The switching frequency in SMPS is generally
A) 50 Hz
B) 1 kHz
C) 20–100 kHz
D) 500 kHz
Answer: C) 20–100 kHz
164. The term “soft switching” refers to
A) Zero current or zero voltage switching
B) Slow switching
C) Low voltage switching
D) Low current switching
Answer: A) Zero current or zero voltage switching
165. In a resonant converter, losses are reduced because
A) Switching occurs at zero voltage/current
B) Low frequency
C) High load current
D) High voltage
Answer: A) Switching occurs at zero voltage/current
166. A DC link converter used in HVDC system consists of
A) Rectifier + Inverter
B) Inverter + Inverter
C) Rectifier + Rectifier
D) Chopper + Inverter
Answer: A) Rectifier + Inverter
167. The DC link inductance in converter system is used to
A) Smooth current
B) Smooth voltage
C) Reduce harmonics
D) Reduce firing delay
Answer: A) Smooth current
168. In dual converter, circulating current is controlled by
A) Reactor
B) Transformer
C) Inductor
D) Resistance
Answer: A) Reactor
169. The purpose of isolation in gate drive circuit is
A) Protect control circuit
B) Reduce power loss
C) Control current
D) Increase voltage
Answer: A) Protect control circuit
170. The firing pulse for SCR is synchronized with
A) AC voltage
B) DC current
C) Gate current
D) Load voltage
Answer: A) AC voltage
171. The power factor of fully controlled converter is
A) Leading
B) Lagging
C) Unity
D) Zero
Answer: B) Lagging
172. The main drawback of half-controlled converter is
A) Limited control range
B) Poor power factor
C) Complex circuit
D) High cost
Answer: A) Limited control range
173. In single-phase full converter, average output voltage is
A)
B)
C)
D)
Answer: A)
174. In inverter, output voltage can be controlled by
A) PWM technique
B) Variable DC link
C) Frequency control
D) All of these
Answer: D) All of these
175. The inverter which uses load commutation is
A) Current source inverter
B) Voltage source inverter
C) Resonant inverter
D) Cycloconverter
Answer: A) Current source inverter
176. The gate drive requirement for IGBT is
A) High current, low voltage
B) Low current, high voltage
C) Low current, low voltage
D) High current, high voltage
Answer: C) Low current, low voltage
177. The thermal runaway in BJT can be prevented by
A) Emitter resistance
B) Collector resistance
C) Base resistance
D) Snubber circuit
Answer: A) Emitter resistance
178. The conduction losses in a power semiconductor are directly proportional to
A) Current
B) Current squared
C) Voltage
D) Power factor
Answer: B) Current squared
179. In power devices, latch-up is a problem in
A) IGBT
B) SCR
C) MOSFET
D) TRIAC
Answer: A) IGBT
180. The reverse recovery characteristic of diode affects
A) Commutation process
B) Output voltage
C) Efficiency
D) Frequency
Answer: A) Commutation process
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