Power factor correction circuit

A power factor correction circuit, also called a PFC (Power Factor Correction) circuit, refers to a circuit designed to improve power quality. Specifically, it is a circuit that performs corrections aimed at bringing the power factor as close to 1 as possible. It works to eliminate the phase difference between voltage and current while simultaneously suppressing harmonic currents.

The suppression of harmonics is regulated by the maximum allowable harmonic current defined by the classes of the international standard IEC 61000-3-2, and related electronic equipment is generally required to incorporate PFC.

Power factor correction circuits are broadly classified into three improvement methods: passive method, partial switching method, and switching method (active method).

The passive method involves directly inserting a reactor into the power supply and is generally used in power circuits with relatively small capacity. The partial switching method adds a switching element to the reactor insertion section of the passive method and performs switching operation during the half cycle period. By turning on the switching element to allow current to flow even during intervals when current would not normally flow, the conduction area of the input current is expanded, thereby improving the power factor. The switching method (active method) inserts a boost converter (boost chopper circuit) between the diode bridge and the load, and improves the power factor by controlling the current through on-off operation to match the phase of the input voltage. Through high-frequency switching operation using a MOSFET or similar device, capacitors and reactors can be designed more compactly.