Class A chopper performance metrics A class A (step-down) chopper has an input voltage of 200 V with Ton = 1.5 ms and Toff = 4.5 ms. Compute (i) the duty cycle, (ii) the average output voltage, and (iii) the ripple factor defined as Vac_rms/Vdc for an ideal resistive load without filtering.

Introduction / Context:
Basic metrics for a step-down chopper include duty cycle (D), average output voltage (Vdc), and ripple factor (defined here as the ratio of the RMS value of the AC component to the DC component). For a rectangular 0–Vin waveform applied to a resistive load, these quantities can be computed directly from Ton and Toff.

Given Data / Assumptions:

• Vin = 200 V.
• Ton = 1.5 ms, Toff = 4.5 ms → switching period T = 6.0 ms.
• Ideal switch; resistive load; no output filter.
• Ripple factor r = Vac_rms / Vdc.

Concept / Approach:

Duty cycle D = Ton/T. Average output voltage for a 0–Vin rectangular wave is Vdc = D * Vin. The total output RMS is Vrms = Vin * sqrt(D). The AC component’s RMS is Vac_rms = sqrt(Vrms^2 − Vdc^2) = Vin * sqrt(D − D^2) = Vin * sqrt(D(1 − D)). Therefore, ripple factor r = Vac_rms / Vdc = sqrt(D(1 − D)) / D = sqrt((1 − D)/D).

Step-by-Step Solution:

Verification / Alternative check:

Limit checks: D → 1 gives r → 0 (pure DC); D → 0.5 gives r = 1; D → very small gives large r, as expected.

Why Other Options Are Wrong:

• Any entry with D = 0.50 or Vavg = 100 V contradicts Ton/Toff values.
• Ripple factor = 1.0 corresponds to D = 0.5, not 0.25.

Common Pitfalls:

Using Vrms/Vdc instead of Vac_rms/Vdc; failing to subtract the DC component when calculating ripple.

Final Answer:

D = 0.25, Vavg = 50 V, ripple factor = 1.732