Answer 6—A bridge rectifier and capacitor power supply has a ripple voltage that is basically a sawtooth waveform at twice the line frequency (120 Hz in North America). The amplitude of the ripple is proportional to the output current and inversely proportional to the size of the capacitor. The charging of the capacitor occurs in extremely narrow pulses at the peaks of the AC waveform.

The output ripple voltage of a power factor controller is basically sinusoidal (distorted slightly) instead of sawtooth. This follows from the fact that the energy transferred into the output capacitor on each switching cycle follows a sinusoidal envelope (the square of the input voltage), while the energy transferred out to the load is essentially constant.

Contributor: David Tweed

Published December 2003