Capacitor Ripple Voltage

ΔV = I / (2 × f × C)

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Result
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Formula

ΔV = I / (2 × f × C)

Description

In a full-wave rectifier or switching converter, the output capacitor charges during each half-cycle and discharges into the load between charge pulses. The peak-to-peak ripple voltage depends on the load current, the ripple frequency (twice the mains frequency for full-wave, or the switching frequency for SMPS), and the capacitance. Reducing ripple requires larger capacitance, higher switching frequency, or lower load current. This is the primary formula for sizing output filter capacitors in power supplies.

Variables

  • ΔV — Peak-to-peak ripple voltage (V)
  • I — DC load current (A)
  • f — Ripple frequency (Hz)
  • C — Filter capacitance (F)

Practical Notes

For a half-wave rectifier, use f (not 2f) as the ripple frequency equals the mains frequency. In switching converters, ESR contributes additional ripple: V_ESR = I_ripple × ESR. The total ripple is approximately √(ΔV² + V_ESR²). Use low-ESR capacitors (ceramic or polymer) when ESR ripple dominates.

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Capacitive Reactance RC Time Constant Capacitor Energy Capacitor Charge Series Capacitance Parallel Capacitance

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