Electronics and Communication Engineering - Power Electronics

Exercise :: Power Electronics - Section 1

26.

Current derating may be necessary when thyristors are operating in

A.	series
B.	parallel
C.	series or parallel
D.	none of the above

Answer: Option B

Explanation:

Since current does not divide equally, current derating is necessary.

27.

If duty cycle is a and the load is a resistance R, the rms value of output voltage is

A.	aV
B.	a V
C.	a²V
D.

Answer: Option B

Explanation:

RMS output voltage

V_L = a V.

28.

For a BJT a = 0.98, then β =

A.	0.02
B.	0.5
C.	4.9
D.	49

Answer: Option D

Explanation:

29.

Assertion (A): Power transistor has lower switching time than SCR

Reason (R): Power transistor has greater switching time than SCR

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

Answer: Option D

Explanation:

Power transistor does not have high rating.

30.

A 3 kV circuit uses SCR of 800 V rating. If derating is 25%, the number of SCRs in series is

A.	4
B.	5
C.	6
D.	8

Answer: Option B

Explanation:

.

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