Power factor correction circuit

A power factor correction circuit, also called a PFC (Power Factor Correction) circuit, is a circuit used to improve power quality. Specifically, it refers to a circuit that aims to bring the power factor as close to 1 as possible. It works to eliminate the difference between voltage and current while also suppressing harmonic currents.

The suppression of harmonics is regulated by the maximum allowable harmonic current according to the class of the international standard IEC 61000-3-2, and PFC is basically required in relevant electronic devices.

There are three main types of power factor correction circuits: passive method, partial switching method, and switching method (active method).

The passive method directly inserts a reactor into the power supply and is generally used in small capacity power supply circuits. The partial switching method adds a switching device to the reactor insertion part of the passive method and performs switching operation during a half-cycle period. By turning on the switching element and allowing current to flow even in previously non-conductive intervals, the conduction area of the input current expands and improves the power factor. The switching method (active method) of the power factor correction circuit inserts a boost converter (boost chopper circuit) between the diode bridge and the load, and improves the power factor by controlling the current through switching and matching the input voltage and phase. High-frequency switching using elements like MOSFETs enables the compact design of components such as capacitors and reactors.