181. In a single-phase full converter, the average output voltage is zero when
A) α = 90°
B) α = 120°
C) α = 180°
D) α = 0°
Answer: C) α = 180°
182. The input power factor of a fully controlled converter decreases with
A) Decrease in firing angle
B) Increase in firing angle
C) Increase in load current
D) Decrease in load resistance
Answer: B) Increase in firing angle
183. For a 3-phase fully controlled converter, the output voltage equation is
A)
B)
C)
D)
Answer: A)
184. A 3-phase full converter operating at α = 0° behaves as
A) Inverter
B) Rectifier
C) Freewheeling circuit
D) Cycloconverter
Answer: B) Rectifier
185. In a boost converter, the inductor stores energy during
A) Switch ON
B) Switch OFF
C) Both ON and OFF
D) Never
Answer: A) Switch ON
186. The main function of a freewheeling diode in a chopper is
A) Reduce voltage stress
B) Provide current path during OFF period
C) Reduce current
D) Maintain voltage
Answer: B) Provide current path during OFF period
187. The average output voltage in a step-down chopper is proportional to
A) Duty cycle
B) Switching frequency
C) Load current
D) Supply voltage
Answer: A) Duty cycle
188. The duty ratio of a boost converter is 0.6. If input voltage is 100 V, output voltage is
A) 150 V
B) 200 V
C) 250 V
D) 400 V
Answer: B) 250 V
189. The output of a single-phase full-bridge inverter using square wave control contains
A) Only fundamental
B) Fundamental + odd harmonics
C) Fundamental + even harmonics
D) DC + AC components
Answer: B) Fundamental + odd harmonics
190. The main advantage of PWM inverter is
A) Lower harmonic distortion
B) Simple circuit
C) Low switching losses
D) High voltage
Answer: A) Lower harmonic distortion
191. The Fourier series of a square wave contains
A) Odd harmonics
B) Even harmonics
C) Both
D) None
Answer: A) Odd harmonics
192. The term “overlap angle” in converters refers to
A) Delay in firing
B) Conduction overlap due to inductance
C) Phase shift
D) Voltage distortion
Answer: B) Conduction overlap due to inductance
193. The commutation failure occurs when
A) Line voltage collapses
B) AC fault occurs
C) High load current
D) All of these
Answer: D) All of these
194. The function of input filter in SMPS is
A) Reduce ripple
B) Reduce EMI
C) Smooth DC voltage
D) Reduce losses
Answer: B) Reduce EMI
195. In a flyback converter, the transformer core stores
A) Energy during switch ON period
B) Energy during switch OFF period
C) No energy
D) Constant energy
Answer: A) Energy during switch ON period
196. The output voltage of a flyback converter is controlled by
A) Duty cycle
B) Frequency
C) Inductance
D) Capacitance
Answer: A) Duty cycle
197. The conduction angle in 3-phase inverter (180° mode) for each device is
A) 180°
B) 120°
C) 90°
D) 60°
Answer: A) 180°
198. The maximum voltage across a thyristor in inverter mode is
A) Peak of supply voltage
B) Twice the supply voltage
C) Half the supply voltage
D) RMS supply voltage
Answer: B) Twice the supply voltage
199. In a single-phase AC regulator using TRIAC, the output RMS voltage is controlled by
A) Phase control
B) Frequency control
C) Amplitude control
D) Pulse control
Answer: A) Phase control
200. The main drawback of AC voltage controllers is
A) Poor input power factor
B) High efficiency
C) Smooth control
D) High cost
Answer: A) Poor input power factor
201. The device suitable for 400 Hz inverter operation is
A) BJT
B) MOSFET
C) SCR
D) TRIAC
Answer: B) MOSFET
202. The base drive circuit for a BJT ensures
A) Proper switching
B) Overcurrent protection
C) Power factor correction
D) Voltage boosting
Answer: A) Proper switching
203. In class-D commutation, SCR is turned off by
A) Reverse current
B) Forward current
C) Zero current
D) Reverse voltage
Answer: D) Reverse voltage
204. The forced commutation requires
A) External circuit
B) Load inductance
C) Transformer
D) Natural zero current
Answer: A) External circuit
205. In current source inverter, commutation failure occurs due to
A) Sudden current change
B) Voltage reversal
C) Load capacitance
D) Gate pulse overlap
Answer: A) Sudden current change
206. In a 3-phase converter, increasing overlap angle
A) Decreases output voltage
B) Increases output voltage
C) Keeps output voltage same
D) Increases efficiency
Answer: A) Decreases output voltage
207. The harmonics in inverter output can be reduced by
A) PWM technique
B) Increasing switching time
C) Decreasing frequency
D) Increasing load
Answer: A) PWM technique
208. A snubber circuit reduces
A) dv/dt
B) di/dt
C) Both dv/dt and di/dt
D) Only current spikes
Answer: C) Both dv/dt and di/dt
209. The turn-off time of SCR is
A) Time to regain forward blocking
B) Time for conduction
C) Time delay in triggering
D) None
Answer: A) Time to regain forward blocking
210. The conduction angle for each SCR in 120° mode inverter is
A) 120°
B) 180°
C) 90°
D) 60°
Answer: A) 120°
211. In voltage source inverter, the output voltage waveform is determined by
A) Switching pattern
B) Load
C) Supply
D) Frequency
Answer: A) Switching pattern
212. The high-frequency transformer in SMPS provides
A) Voltage isolation
B) Voltage regulation
C) Rectification
D) Filtering
Answer: A) Voltage isolation
213. In DC link converter, the DC voltage ripple is minimized by
A) Inductance
B) Capacitance
C) Resistance
D) Transformer
Answer: B) Capacitance
214. The main function of snubber capacitor is to
A) Absorb voltage spikes
B) Increase conduction
C) Store charge
D) Filter noise
Answer: A) Absorb voltage spikes
215. The function of gate resistor in MOSFET driver is
A) Control switching speed
B) Reduce losses
C) Increase voltage
D) Reduce noise
Answer: A) Control switching speed
216. In IGBT, latch-up occurs due to
A) Parasitic thyristor action
B) High frequency
C) High temperature
D) Gate voltage variation
Answer: A) Parasitic thyristor action
217. In a full converter, the reactive power drawn increases with
A) Increase in α
B) Decrease in α
C) Constant α
D) Zero α
Answer: A) Increase in α
218. The commutation circuit in chopper helps in
A) Turn off main device
B) Turn on main device
C) Maintain current
D) Reduce voltage
Answer: A) Turn off main device
219. In DC chopper, current ripple can be reduced by
A) Increasing inductance
B) Decreasing frequency
C) Decreasing capacitance
D) Increasing resistance
Answer: A) Increasing inductance
220. The most suitable device for low-voltage high-frequency switching is
A) MOSFET
B) IGBT
C) SCR
D) BJT
Answer: A) MOSFET
221. The switching losses are proportional to
A) Frequency
B) Frequency × Voltage × Current
C) Voltage²
D) Current²
Answer: B) Frequency × Voltage × Current
222. The efficiency of converter improves when
A) Switching losses decrease
B) Ripple increases
C) Frequency decreases
D) Output current increases
Answer: A) Switching losses decrease
223. The PWM control in inverter allows
A) Harmonic control
B) Speed control
C) Voltage control
D) All of these
Answer: D) All of these
224. The commutation circuit is not needed for
A) MOSFET
B) SCR
C) GTO
D) Thyristor
Answer: A) MOSFET
225. The conduction losses depend mainly on
A) On-state resistance
B) dv/dt
C) Switching frequency
D) Gate drive
Answer: A) On-state resistance
226. The safe operating area of MOSFET depends on
A) Voltage, current, and temperature
B) Frequency only
C) Voltage only
D) Current only
Answer: A) Voltage, current, and temperature
227. In SMPS, the output voltage ripple is minimized by
A) Output capacitor
B) Transformer
C) Load resistance
D) Duty cycle
Answer: A) Output capacitor
228. The current sharing among parallel SCRs is improved by
A) Series inductors
B) Magnetic coupling
C) Equalizing resistors
D) Diode coupling
Answer: C) Equalizing resistors
229. The commutation angle is the interval between
A) Firing and current zero
B) Current zero and voltage zero
C) Current reversal
D) Firing of successive SCRs
Answer: D) Firing of successive SCRs
230. The purpose of RCD snubber circuit is
A) Energy absorption and protection
B) Current limiting
C) Frequency control
D) Harmonic elimination
Answer: A) Energy absorption and protection
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