Calculate capacitor ripple voltage, or the smoothing capacitor size you need, from load current and ripple frequency, with optional ESR and percent ripple.

The frequency the capacitor recharges at: twice the mains frequency for a full-wave bridge, equal to it for half-wave.

ESR and peak voltage
Blank means 0 Ω. ESR adds I × ESR to the ripple.

Optional. Adds percent ripple, ripple factor and the approximate DC output voltage.

Related Calculators

Capacitor Ripple Voltage Formula

The capacitor ripple voltage calculation is based on the charge-discharge relationship for a smoothing capacitor:

Vpp = I / (f × C)
  • Vpp = peak-to-peak ripple voltage, in volts (V)
  • I = load or discharge current, in amperes (A)
  • f = ripple frequency, in hertz (Hz)
  • C = capacitance, in farads (F)

The same relationship can be rearranged to calculate any missing value:

I = Vpp × f × C
f = I / (Vpp × C)
C = I / (f × Vpp)

If you enter load current, ripple frequency, and capacitance, the calculator finds peak-to-peak ripple voltage. Choose Required capacitance instead to find the capacitance for an allowable ripple voltage. All values are converted to base units first: amperes, hertz, farads, and volts.

Common Ripple Frequency Values

Ripple frequency depends on the circuit that is charging the capacitor. Use the ripple frequency seen by the capacitor, not always the mains frequency.

Circuit type Input frequency Typical ripple frequency
Half-wave rectifier 50 Hz mains 50 Hz
Half-wave rectifier 60 Hz mains 60 Hz
Full-wave bridge rectifier 50 Hz mains 100 Hz
Full-wave bridge rectifier 60 Hz mains 120 Hz
Switching power supply output capacitor Switching frequency Usually the switching frequency, or a related harmonic

Capacitance Unit Reference

Unit Meaning Farads equivalent
F farad 1 F
mF millifarad 0.001 F
µF microfarad 0.000001 F
nF nanofarad 0.000000001 F

Example Calculations

Example 1: Calculate ripple voltage

You have a 0.5 A load, a 120 Hz ripple frequency, and a 2200 µF capacitor.

C = 2200 uF = 0.0022 F
Vpp = 0.5 / (120 × 0.0022) = 1.8939 V

The peak-to-peak ripple voltage is about 1.89 V.

Example 2: Calculate required capacitance

You want to keep ripple voltage to 0.25 V with a 1 A load and 100 Hz ripple frequency.

C = 1 / (100 × 0.25) = 0.04 F
0.04 F = 40000 uF

The required capacitance is 0.04 F, or 40,000 µF.

FAQs

Is capacitor ripple voltage peak-to-peak or RMS?

This calculator uses peak-to-peak ripple voltage. That means it estimates the voltage difference between the highest and lowest points of the capacitor voltage during one ripple cycle. RMS ripple voltage is a different value and depends on the waveform shape.

Does this formula include capacitor ESR?

No. The formula Vpp = I / (f × C) estimates ripple caused by capacitor discharge. Real capacitors also have equivalent series resistance, or ESR, which can add extra ripple voltage:

Vesr = Iripple × ESR

For low-voltage or high-current supplies, ESR ripple can be significant and should be checked separately.

Why does higher capacitance reduce ripple voltage?

A larger capacitor stores more charge for the same voltage change. During the time between charging pulses, it can supply the load current with a smaller voltage drop. In the formula, capacitance is in the denominator, so increasing capacitance lowers the calculated ripple voltage.