Question

A step-up chopper has input voltage of 220 V and output voltage of 660 V. If the conducting time of the IGBT based chopper is 100 μs, compute Toff width of the output voltage pulse.

(a) 100 μs

(b) 150 μs

(c) 50 μs

(d) Insufficient data

This question was posed to me in an interview for internship.

My question is based upon Choppers-3 topic in section Choppers of Power Electronics

Answer 1

The correct choice is (c) 50 μs

To elaborate: 660 = 220/1-α

α = 2/3 = Ton/T

Ton = 2T/3 = 100μs. This gives chopping period T = 100 x 3/2 = 150 μs

Toff = T – Ton = 150 – 100 = 50 μs.