APFC

APFC stands for Active Power Factor Correction, a technique used in power electronics to improve the power factor of alternating-current to direct-current power supplies. By shaping the input current to follow the input voltage waveform, APFC reduces current distortion and increases the fraction of delivered power that is usable by the load.

Most APFC implementations use a boost converter controlled by a feedback loop. The input current is sensed and compared to a reference that mirrors the AC voltage waveform. A control circuit generates switching commands for a power transistor, regulating the boost stage so that the drawn current is nearly in phase with the line voltage. This results in an input current that is closer to a sine wave and reduces harmonic content.

Architectures vary: in single-stage APFC the correction is integrated with the main power conversion, while in two-stage designs an APFC pre-regulator sits before a separate DC-DC stage. Common components include an inductor, switching transistor, diode, and a dedicated APFC controller or IC.

APFC is widely used in computer power supplies, consumer electronics, and industrial power supplies to meet electrical standards and improve efficiency. Benefits include higher input power factor, lower line current distortion, reduced peak demand, and easier compliance with standards such as IEC 61000-3-2. Challenges include added cost and complexity, potential EMI concerns, and the need for robust control to maintain performance across varying loads and line conditions.