201. The harmonic distortion in inverter output can be reduced by
A) Increasing switching frequency
B) Using filters
C) Using PWM
D) All of these
Answer: D) All of these
202. The turn-off time of SCR is the time between
A) Anode current falling to zero and SCR regaining blocking ability
B) Gate pulse and current zero
C) Current zero and voltage zero
D) Firing instant and conduction start
Answer: A) Anode current falling to zero and SCR regaining blocking ability
203. The commutation process that uses LC components is called
A) Resonant commutation
B) Load commutation
C) Natural commutation
D) Forced commutation
Answer: A) Resonant commutation
204. In a full-wave rectifier, the ripple frequency is
A) Equal to supply frequency
B) Twice supply frequency
C) Half supply frequency
D) Zero
Answer: B) Twice supply frequency
205. The main advantage of using PWM technique is
A) Reduced harmonic content
B) Constant output frequency
C) High efficiency
D) All of these
Answer: D) All of these
206. The output voltage of a single-phase full converter for α = 90° is
A) Zero
B) Vm/2
C) Vm/π
D) Negative
Answer: A) Zero
207. A GTO can be turned off by
A) Reverse gate current
B) Forward gate current
C) Reverse anode current
D) None
Answer: A) Reverse gate current
208. The primary function of snubber circuit is to
A) Absorb voltage spikes
B) Improve conduction
C) Reduce switching frequency
D) Control duty cycle
Answer: A) Absorb voltage spikes
209. The forward blocking mode of SCR means
A) SCR is forward biased but not triggered
B) SCR is reverse biased
C) SCR conducts
D) None
Answer: A) SCR is forward biased but not triggered
210. The control range of firing angle α in converter is
A) 0° to 90°
B) 0° to 180°
C) 90° to 180°
D) 0° to 270°
Answer: B) 0° to 180°
211. The inverter output waveform without PWM is
A) Square wave
B) Sine wave
C) Triangular wave
D) Pulse wave
Answer: A) Square wave
212. In a three-phase half-wave converter, the number of SCRs used is
A) 3
B) 6
C) 4
D) 2
Answer: A) 3
213. The output voltage of step-down chopper is proportional to
A) Duty cycle
B) Inductance
C) Switching frequency
D) Capacitance
Answer: A) Duty cycle
214. A current commutated chopper is also known as
A) Class A
B) Class B
C) Class C
D) Class D
Answer: D) Class D
215. The device used in high voltage, high current applications is
A) GTO
B) MOSFET
C) BJT
D) TRIAC
Answer: A) GTO
216. In a boost converter, inductor current flows
A) During both ON and OFF period
B) Only during ON period
C) Only during OFF period
D) None
Answer: A) During both ON and OFF period
217. The conduction angle in full converter is
A) 180°
B) 90°
C) Variable
D) 360°
Answer: A) 180°
218. The instantaneous output voltage of a single-phase half converter is
A) Vm sinωt
B) Vm sinωt for α ≤ ωt ≤ π
C) Constant DC
D) Zero
Answer: B) Vm sinωt for α ≤ ωt ≤ π
219. The inverter which gives better harmonic performance is
A) PWM inverter
B) Square wave inverter
C) Resonant inverter
D) Current source inverter
Answer: A) PWM inverter
220. The commutation method used in choppers with inductive load is
A) Forced commutation
B) Natural commutation
C) Load commutation
D) Resonant commutation
Answer: A) Forced commutation
221. The major limitation of SCR in high-frequency applications is
A) Long turn-off time
B) High voltage drop
C) High current
D) Low input impedance
Answer: A) Long turn-off time
222. The frequency of output voltage in inverter depends on
A) Switching frequency
B) Supply voltage
C) Load current
D) Firing angle
Answer: A) Switching frequency
223. The typical gate voltage required to trigger an SCR is about
A) 0.1–1 V
B) 1–3 V
C) 3–10 V
D) 10–15 V
Answer: B) 1–3 V
224. The conduction angle of full converter is
A) 90°
B) 180°
C) Variable with α
D) 360°
Answer: B) 180°
225. The switching losses in MOSFETs are mainly due to
A) Gate charge
B) Drain-source voltage overlap
C) Reverse recovery
D) Capacitance
Answer: B) Drain-source voltage overlap
226. The main feature of VSI is
A) Constant DC input
B) Constant current output
C) Constant voltage output
D) Variable voltage input
Answer: A) Constant DC input
227. The inverter used in UPS systems is
A) PWM inverter
B) Current source inverter
C) Resonant inverter
D) Series inverter
Answer: A) PWM inverter
228. The device suitable for medium power, medium frequency is
A) IGBT
B) MOSFET
C) GTO
D) TRIAC
Answer: A) IGBT
229. The turn-off gain of GTO is defined as the ratio of
A) Anode current to gate current
B) Gate current to anode current
C) Gate voltage to anode current
D) Anode voltage to gate voltage
Answer: A) Anode current to gate current
230. In current commutation, energy is stored in
A) Inductor
B) Capacitor
C) Both
D) None
Answer: B) Capacitor
231. The ripple factor of single-phase full-wave rectifier is approximately
A) 0.482
B) 1.21
C) 0.707
D) 0.612
Answer: A) 0.482
232. The control of power factor in converter is achieved by
A) Phase control
B) PWM control
C) Feedback
D) Firing delay
Answer: D) Firing delay
233. The number of SCRs in a three-phase full converter is
A) 3
B) 4
C) 6
D) 2
Answer: C) 6
234. The form factor of half-wave rectifier is
A) 1.11
B) 1.57
C) 2.0
D) 0.707
Answer: B) 1.57
235. The device used for bidirectional current control is
A) TRIAC
B) SCR
C) MOSFET
D) Diode
Answer: A) TRIAC
236. The firing circuit of SCR provides
A) Trigger pulse
B) Commutation
C) Reverse voltage
D) None
Answer: A) Trigger pulse
237. The term “cycloconverter” means
A) AC to AC conversion
B) DC to DC conversion
C) AC to DC conversion
D) DC to AC conversion
Answer: A) AC to AC conversion
238. The inverter used for variable frequency drive is
A) PWM inverter
B) Cycloconverter
C) Series inverter
D) Single-phase inverter
Answer: A) PWM inverter
239. The device most suitable for low voltage, low power applications is
A) MOSFET
B) IGBT
C) GTO
D) SCR
Answer: A) MOSFET
240. The frequency of inverter output can be varied by
A) Varying switching frequency
B) Varying voltage
C) Varying current
D) Varying duty cycle
Answer: A) Varying switching frequency
241. The freewheeling diode improves
A) Load current continuity
B) Power factor
C) Voltage regulation
D) All of these
Answer: D) All of these
242. The input to inverter is
A) DC
B) AC
C) Pulsating DC
D) Rectified AC
Answer: A) DC
243. The inverter output voltage depends on
A) Input voltage and switching pattern
B) Frequency only
C) Duty cycle
D) None
Answer: A) Input voltage and switching pattern
244. The turn-on losses are reduced by
A) Fast gate drive
B) Snubber circuit
C) Soft switching
D) All
Answer: D) All
245. The heat sink thermal resistance should be
A) Low
B) High
C) Medium
D) Variable
Answer: A) Low
246. The safe operating area of device is affected by
A) Voltage
B) Current
C) Temperature
D) All
Answer: D) All
247. The control ratio of chopper is
A) Vo(max)/Vo(min)
B) Vo/Vin
C) Vin/Vo
D) Ton/Toff
Answer: A) Vo(max)/Vo(min)
248. The conduction loss in inverter depends on
A) Device on-state voltage drop
B) Load current
C) Both A and B
D) None
Answer: C) Both A and B
249. The SCR is used for
A) Power control
B) Speed control
C) Phase control
D) All of these
Answer: D) All of these
250. The natural commutation occurs when
A) Current naturally passes through zero
B) Voltage forced to zero
C) Gate pulse removed
D) Load is inductive
Answer: A) Current naturally passes through zero
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