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 performs correction with the aim of 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 PFC is generally required for related electronic equipment.

Power factor correction circuits can be broadly classified into three types: passive method, partial switching method, and switching (active) method.

The passive method directly inserts a reactor into the power supply and is generally used for power circuits with 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 and allowing current to flow even during intervals when no current would normally flow, the conduction area of the input current is expanded and the power factor can be improved. In the switching (active) method, a boost converter (boost chopper circuit) is inserted between the diode bridge and the load, and the current is controlled by turning it on and off to match the phase of the input voltage and current, thereby improving the power factor. Through high-frequency switching operation using MOSFETs or similar devices, capacitors and reactors can be designed more compactly.