Electronics and Communication Engineering - Power Electronics

11. 

An SCR is triggered at 40° in the positive half cycle only. The average anode current is 50 A. If the firing angle is changed to 80°, the average anode current is likely to be

A. 50 A
B. 25 A
C. less than 50 A but more than 25 A
D. less than 25 A

Answer: Option C

Explanation:

.


12. 

The characteristics of a non-linear resistance is i = kv4. If i becomes 100 times, v becomes

A. about 100 times
B. about 10 times
C. about 3 times
D. about twice

Answer: Option C

Explanation:

v ∝ (i)1/4 ∝ (100)1/4 ≈ 3.


13. 

In a step down chopper using pulse width modulation, Ton = 3 x 10-3 and Toff = 1 x 10-3 s. The chopping frequency is

A. 333.33
B. 250
C. 500
D. 1000

Answer: Option B

Explanation:

.


14. 

Thyristors are suitable for dc circuit breakers but not for ac circuit breakers.

A. True
B. False

Answer: Option B

Explanation:

They are suitable for both dc and ac circuit breakers.


15. 

Assertion (A): Inverters and choppers use fast switching thyristors

Reason (R): Fast switching SCR has low turn off time.

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 A

Explanation:

Low turn off time enables fast switching.