Figure shows a chopper feeding RLE load, The free wheeling diode conducts when t

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Question
Figure shows a chopper feeding RLE load, The free wheeling diode conducts when
Options
A. thyristor is on
B. thyristor is off
C. both when thyristor is on and thyristor is off
D. partly when thyristor is off and partly when thyristor is on

Correct Answer

thyristor is off

Explanation

FD is forward biased only when thyristor is off.

Power Electronics problems

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2. In a single phase full wave converter (M - 2 connection) feeding a highly inductive load, the firing angle for each thyristor is a in the respective half cycle. The period of conduction of each thyristor is
Options
A. p - a
B. p
C. p + a
D. p - 2a

3. The terminals of a power BJT are called
Options
A. emitter, base, collector
B. emitter, base, drain
C. source, base, drain
D. source, base, collector

5. Assertion (A): Inverters and choppers use fast switching thyristors
Reason (R): Fast switching SCR has low turn off time.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

6. A chopper
Options
A. converts constant voltage dc into ac and then into variable voltage dc
B. converts constant voltage dc into variable voltage dc directly
C. converts ac of one frequency into ac of another frequency
D. converts ac to dc

7. Assertion (A): If the duty cycle of chopper is low the current would not become discontinuous
Reason (R): If the time constant L/R of the load in chopper is low the current may become discontinuous.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

8. In a thyristor the gate current is increased, then
Options
A. anode current will increase
B. anode current will decrease
C. anode current will remain constant
D. anode current may increase or decrease

9. Assertion (A): An ideal rectifier should have unity harmonic factor
Reason (R): An ideal rectifier should have unity displacement factor.
Options
A. Both A and R are correct and R is correct explanation of A
B. Both A and R correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct

10. A thyristor has a maximum allowable junction temperature of 120�C and the ambient temperature is 40�C. If thermal resistance is 1.6� C/W, the maximum allowable internal power dissipation is
Options
A. 20 W
B. 50 W
C. 92 W
D. 128 W

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