Power Factor Correction (PFC)

An active or passive Power Factor Correction (PFC) filter is an electrical or electronic circuit that increases the so-called power factor so that it remains within a legally prescribed range.
It compensates phase shifts that would lead to reactive power and harmonics and associated interference. The power factor is described by a value that should be as close as possible to magnitude 1. The usual compensation values are in the range around 0.98.
In the case of non-linear loads, i.e. mainly rectifiers with subsequent smoothing in switching power supplies, phase-shifted and non-sinusoidal input currents occur with sinusoidal AC voltage supply. These consist of a sum of higher-frequency components, i.e. harmonics, which can cause interference in the power supply networks and other electrical devices.

Two variants are common:
Passive harmonic filters (passive PFC) These are usually chokes with high inductance. Passive filters are easy to manufacture, but achieve only moderately good results.
Active harmonic filters (Active PFC) The circuits required for this are more complex, but achieve a very good power factor correction of typically 0.98. The power factor correction is typically 0.98.

Active PFC circuits usually consist of a rectifier with an upwards converter connected directly downstream, which charges a large capacitor to a voltage above the peak voltage of the AC mains voltage (typ. 350...400 V) (also called DC link voltage). Furthermore, an active PFC can compensate for mains voltage fluctuations. It is often dimensioned in such a way that devices equipped with it can operate worldwide on all mains voltages without switching (wide range input of typically 100...240 V).
The active PFC generates additional high-frequency interference, which must be suppressed by an upstream passive mains filter. Back