What is the formula for Rectifier Ripple Factor?

The Rectifier Ripple Factor formula is r = √((Vrms / Vdc)² − 1), where r—Ripple factor (fraction); Vrms—Total RMS of the output (DC + ripple) (V); Vdc—DC (average) component (V).

Rectifier Ripple Factor

Q: How do you calculate Rectifier Ripple Factor?

Use the formula r = √((Vrms / Vdc)² − 1). The ripple factor measures how much residual AC remains on a rectified, filtered DC output, defined as the ratio of the RMS ripple to the DC value. Enter the values you know in the calculator above and it solves for the remaining variable.

r = √((Vrms/Vdc)² − 1)

Calculator

Ripple Factor

Output RMS Voltage

Output DC Voltage

Result

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Formula

r = √((Vrms / Vdc)² − 1)

Description

The ripple factor measures how much residual AC remains on a rectified, filtered DC output, defined as the ratio of the RMS ripple to the DC value. It is the standard figure of merit for a power-supply filter: a smaller ripple factor means cleaner DC. An unfiltered half-wave output has r ≈ 1.21 and full-wave ≈ 0.48; a reservoir capacitor brings it down to a few percent.

Variables

r — Ripple factor (fraction)
Vrms — Total RMS of the output (DC + ripple) (V)
Vdc — DC (average) component (V)

Practical Notes

Multiply by 100 for a percentage. Adding a filter capacitor or an LC/π filter reduces r dramatically; linear regulators then reject the rest.

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