# Power Electronics Power Electronics
| Power Electronics |
Q.1
Circuit turn-off time of an SCR is defined as the time
A. taken by the SCR turn of
B. required for the SCR current to become zero
C. for which the SCR is reverse biased by the commutation circuit
D. for which the SCR is reverse biased to reduce its current below the holding current
Answer : Option C
Explaination / Solution:
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Q.2
A three-phase current source inverter used for the speed control of an induction motor is to be realized using MOSFET switches as shown below. Switches S1 to S6 are identical switches. The proper configuration for realizing switches S1 to S6 is
A. B. C. D. Answer : Option C
Explaination / Solution:
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Q.3
The transistor used in the circuit shown below has a β of 30 and ICBO is negligible If the forward voltage drop of diode is 0.7V, then the current through collector will be
A. 168 mA
B. 108 mA
C. 20.54mA
D. 5.36 mA
Answer : Option D
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Q.4
A voltage commutated chopper circuit, operated at 500Hz, is shown below. If the maximum value of load current is 10A, then the maximum current through the main (M) and auxiliary (A) thyristors will be
A. B. C. D. Answer : Option A
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Q.5
A clipper circuit is shown below. Assuming forward voltage drops of the diodes to be 0.7V, the input-output transfer characteristics of the circuit is
A. B. C. D. Answer : Option C
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Q.6
A single-phase thyristor-bridge rectifier is fed from a 230 V, 50 Hz, single-phase AC mains. If it is delivering a constant DC current of 10 A, at firing angle of 30º, then value of the power factor at AC mains is
A. 0.87
B. 0.9
C. 0.78
D. 0.45
Answer : Option C
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Q.7
A single-phase full-bridge voltage source inverter (VSI) is fed from a 300 V battery. A pulse of 120º duration is used to trigger the appropriate devices in each half-cycle. The rms value of the fundamental component of the output voltage, in volts, is
A. 234
B. 245
C. 300
D. 331
Answer : Option A
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Q.8
The typical ratio of latching current to holding current in a 20 A thyristor is
A. 5.0
B. 2.0
C. 1.0
D. 0.5
Answer : Option B
Explaination / Solution:
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Q.9
A half-controlled single-phase bridge rectifier is supplying an R-L load. It is operated at a firing angle α and the load current is continuous. The fraction of cycle that the freewheeling diode conducts is
A. 1/2
B. C. D. Answer : Option D
Explaination / Solution:
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Q.10
The i-v characteristics of the diode in the circuit given below are The current in the circuit is A. 10 mA
B. 9.3 mA
C. 6.67 mA
D. 6.2 mA
Answer : Option D
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