power factor correction (PFC)

A circuit that makes a power supply draw current politely in step with the mains voltage, like sipping steadily from a straw instead of gulping in spikes. A naive rectifier-plus-capacitor only gulps current at the AC peaks, drawing a spiky waveform that wastes grid capacity and pollutes it with harmonics. PFC reshapes that draw into a clean sine in phase with the voltage.

An active PFC stage — usually a boost converter clever enough to track the input sine — pushes the power factor from a sloppy 0.6 up toward 0.99. That matters: utilities and standards (like IEC 61000-3-2) demand it above ~75 W because poor power factor forces the grid to carry extra current it can't bill for. Every PC and server power supply has one tucked in the front end.