Question

Find the expression for output voltage for a step-up chopper, assume linear variation of load current and α as the duty cycle.

(a) Vs

(b) Vs/α

(c) Vs/(1-α)

(d) Vs/√2

This question was addressed to me during an interview.

The origin of the question is Choppers-2 topic in section Choppers of Power Electronics

Answer 1

The correct option is (c) Vs/(1-α)

Easiest explanation: During Ton, the energy stored in the inductor is

Win = Vs x Ton x (I1+I2)/2

During Toff, the energy released by the inductor is

Wout = (Vo – Vs) x Toff x (I1+I2)/2

Considering ideal condition,

Win = Wout

Vo = Vs x (T/Toff)

α = Ton/T

Vo = T/T-Ton = Vs/1-α.