Ripple Current Calculator — InnovChip

Ripple Current Calculator

Estimate input-capacitor RMS ripple current for a buck converter and the output ripple amplitude from duty cycle and load current.

Calculator

About This Calculator

In a buck converter the input capacitor carries a triangular AC current that equals the load current folded by the duty cycle. RMS ripple is maximized near D = 0.5 (I/2 RMS). Output ripple is dominated by the inductor ripple current times the capacitor ESR plus the charge/discharge term. This tool estimates both the input-cap stress and the output ripple voltage.

How to Use

  1. Enter the buck load current and the operating duty cycle.
  2. Enter the allowed/reference inductor ripple as a percentage of output current (rule of thumb 20-40%).
  3. Set the output capacitor ESR (MLCC ~1-5 mΩ; standard electrolytic 50-500 mΩ).
  4. The input RMS figure sizes your input capacitor ripple rating (derate for frequency/temperature).

Formulas

Input RMS rippleI(rms) = I(out) × √(D·(1−D))
Inductor rippleΔI(L) = I(out) × Ripple%
ESR rippleΔV = ΔI(L) × ESR

Design Notes

Choose input caps with ripple rating ≥ computed RMS; ceramic caps are typically fine, electrolytic need margin.

For output ripple add the ESL term at high frequencies — ESR only is an approximation.