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Electronics Engineering Objective Questions { Power Semiconductor Devices and Their Applications }

183. An SCR can withstand a maximum junction temperature of 120?C with an ambient temperature of 75?C, If the SCR has thermal resistance from junction to ambient as 1.5?C/W, the maximum internal power dissipation allowed is
A. 30 W
B. 60 W
C. 80 W
D. 50 W
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184. A single-phase half-wave controlled rectifier has 400 sin 314 t as the input voltage and R as the load. For the firing angle of 600 for the SCR, the average output voltage is
A. 400/71
B. 300/7c
C. 240/7c
D. 200/n
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185. A single-phase, one-pulse controlled circuit has resistance and counter emf load and 400 sin 314t as the source voltage. For a load counter emt of 200 V, the range of firing angle control is
A. 30? to 150?
B. 30? to 1800
C. 60? to 120?
D. 60? to 180?
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186. The uncontrolled electronic switch employed in power-electronic converters is
A. thyristor
B. bipolar junction transistor
C. diode
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187. In a commutation circuit employed to turn off an SCR, satisfactory turn-off is obtained when
A. circuit turn-off time < device turn-off time
B.circuit turn-off time > device turn-off time
C. circuit time constant > device turn-off time
D. circuit time constant < device turn-off time
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188.  If a diode connected in anti-parallel with thyristor, then
A. both turn-off power loss and turn-off time decreases
B.turn-off power loss decreases but turnoff time increases
C. turn-off power loss increases, but turn-off time decreases
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189. In a dual converter, the circulating current
A. allows smooth reversal of load current, but increases the response time
B.does not allow smooth reversal of load current
C. allows smooth reversal of load current with improved speed of response
D. flows only if there is no interconnecting inductor
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