# Electronics and Communication Engineering - Power Electronics

### Exercise :: Power Electronics - Section 1

16.

The value of capacitor C for dynamic equalising circuit of series connected thyristors is determined by

 A. forward characteristics of thyristors B. reverse recovery characteristics of thyristors C. both forward and reverse recovery characteristics of thyristors D. none of the above

Explanation:

Value of C is proportional to maximum difference between reverse charge of SCRs in series.

17.

A chopper

 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

Explanation:

A chopper is a dc-ac converter. It converts a fixed dc voltage into a variable dc voltage.

18.

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.

 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

Explanation:

If duty cycle is low, current may become discontinuous.

19.

In a single phase full wave regulator, the firing angles in the positive and negative half cycles are generally

 A. equal B. different C. equal or different D. different but sometimes equal

Explanation:

Firing angles are kept equal to get symmetrical output voltage.

20.

An electric heater is controlled by thyristors through on-off control. If a = 0.4, the heating is

 A. 16% maximum B. 40% of maximum C. 60% of maximum D. 84% of maximum