Abstract: A power factor correction apparatus which uses Pulse Frequency Modulation (PFM) to control an AC/DC converter is disclosed. Only a current signal from the converter is used to determine the switching frequency. Sensing of the input line voltage is not needed. The switching frequency varies with the line voltage such that the converter emulates a resistive load. By using PFM control, EMI is spread over a range rather than concentrated at a few frequencies. Thus a smaller EMI filter can be used. Since the switching frequency decreases with the loading of the converter, the switching loss decreases with the loading as well. Thus, the need of meeting efficiency standards, e.g. the 80 PLUS and Energy Star, can be fulfill without extra circuitry.

Abstract: A power factor correction method and apparatus which use Pulse Frequency Modulation (PFM) to control an AC/DC converter is disclosed. The average current drawn by the AC/DC converter is compared with a reference sinusoidal signal and the error is used to determine the switching frequency. The switching frequency varies with the sinusoidal reference signal such that the converter emulates a resistive load. By using PFM control, EMI is spread over a range rather than concentrated at a few frequencies. Since the switching frequency decreases with the loading of the converter, the switching loss decreases with the loading as well. Thus, the need of meeting efficiency standards, e.g. the 80 PLUS and Energy Star, can be fulfill without extra circuitry.