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The given figure shows a step-down chopper switched at 1 kHz with a duty ratio α = 0.5. The peak to peak value of ripple current  in the load current is close to

The given figure shows a step-down chopper switched at 1 kHz with a duty ratio α = 0.5. The peak to peak value of ripple current  in the load current is close to Correct Answer 0.125 A

Concept:

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In a step down chopper-

The inductor is assumed to be having sufficient energy to support the conduction throughout half time

Average output voltage 

V0 = αVs

RMS value of output voltage

Vor = √α Vs

Where, Vs = Supply voltage

Ton = αT

Toff = (1 - α)T

T = 1/f

Where, T is total time period

f is switching frequency

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Per unit Ripple (or) Ripple is a function of duty cycle ‘α’

As shown in figure, ripple is minimum at α = 0, increases maximum at α = 0.5 and decreases at α = 1.0 

The peak to peak value of ripple current is

i0 = Ton ( Vs - V0) / L = Toff (V0) / L

  • This shows that the maximum value of ripple current is inversely proportional to chopping frequency and the circuit inductance.
  • For the better performance of the load, the conduction to be continuous. It is preferable to have less value of the current ripple (or) More uniform output current. The chopping frequency is to be high. It is possible by employing the smaller values of the time period.

Calculation:

Given-

α = 0.5, L = 200 mH, f = 1 kHz, Vs = 100 V

V0 = 0.5 x 100 = 50 V

T = 1 / 1000

Ton = 0.5 x 10-3

i0 = 0.5 x 10-3 (100 - 50) / (200 x 10-3)

i0 = 0.125 A

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