PFC(Power Factor Correction,PFC (Power Factor Correction) circuits were initially used more frequently in UPS power supplies, but were rarely seen in low-power power supplies (such as PCs). However, with the emergence of mandatory certifications (such as CCC), PFC has become increasingly popular in low-power power supplies.
PFC circuits are categorized as passive and active. A passive PFC circuit is essentially a power-frequency inductor made of silicon steel sheets. It leverages the principle that the current within the inductor coil cannot change suddenly to adjust the phase difference between the voltage and current in the circuit, making the current tend toward a sinusoidal state and improving the power factor. An active PFC circuit, on the other hand, consists of components such as a high-frequency inductor, a switching transistor, and a capacitor. It can be simply described as a boost-type switching power supply circuit. It converts 110V or 220V AC mains power to a high-voltage DC voltage of approximately 380V.
Most PFC circuits use a boost topology, which separates the rectifier circuit from the large filter capacitor. By controlling the conduction of the PFC switch, the input current can be adjusted to follow the input voltage. In this circuit, the PFC inductor L stores energy when the MOS switch Q is on. When the switch is off, the inductor L induces a voltage that is positive on the right and negative on the left. This stored energy charges the large filter capacitor through the boost diode DI. The large energy storage filter capacitor C and the PFC inductor L are connected in series after the PFC circuit. Because the current in L cannot change suddenly, it can limit the inrush current of the large filter capacitor C.
The PFC inductor is a core component of the PFC circuit. Common PFC inductors include amorphous PFC inductors and Sendust PFC inductors. Amorphous PFC inductors are made of iron-based amorphous ribbon with an open core. They offer excellent frequency characteristics and stable operation, strong constant inductance, excellent DC bias resistance, and low losses. Amorphous PFC inductors can be used in variable-frequency power supplies, UPSs, switching power supplies, inverters, industrial power supplies, and telecommunication power supplies. Sendust PFC inductors, with a core made of Sendust material, have a Curie temperature above 410°C and an operating temperature range of -50°C to +200°C. They exhibit excellent current superposition performance, low core losses, and a negative temperature coefficient. Sendust PFC inductors are suitable for power supplies, uninterruptible power supplies (UPSs), and various home appliance control boards.
