Question

In the below given circuit, when switch (SW) is first switched closed and then opened the

(a) voltage is non-zero and current is rising

(b) voltage is zero and current is decaying

(c) voltage is non-zero and current is decaying

(d) voltage is zero and current is rising

I had been asked this question at a job interview.

This is a very interesting question from Choppers-2 in portion Choppers of Power Electronics

Answer 1

Correct choice is (c) voltage is non-zero and current is decaying

To elaborate: When the switch is off, the inductor is has stored energy from the earlier chopper on operation. The current starts to flow from Vs-L-D-Load-Vs, hence current is decaying as the inductor is discharging and the voltage is Vs + Vl (inductor voltage) (apply KVL).