Definition
Power Factor Correction (PFC) is the front-end circuitry inside a switch-mode power supply that forces the current drawn from the AC line to track the line voltage waveform. Without it, the bulk rectifier and capacitor pull current in short, high peaks that distort the line, produce harmonic pollution, and force the utility to deliver more apparent power than the real power actually consumed. For a high-draw load like a Bitcoin mining ASIC pulling 3kW or more, a poor power factor wastes capacity on every branch circuit it shares.
Active vs. passive PFC
Passive PFC uses bulk inductors and is rarely seen in modern high-density supplies. Active PFC is the standard in ASIC and server PSUs: a boost pre-converter raises the rectified, unfiltered AC into a regulated DC rail (typically around 375-400V) while a controller modulates the switch so input current stays in phase with line voltage. A well-designed single-stage active PFC stage can reach near-unity power factor and push total harmonic distortion below 8%.
Why miners should care
A power factor near 1.0 means the breaker rating you paid for is fully usable, fewer machines trip a circuit, and the facility presents a cleaner load to the grid. Many ASIC supplies are rated for both 120V and 240V partly because the active PFC boost stage adapts across that input range. Power factor is also what utility demand charges and three-phase balancing calculations key off of.
For how PFC sits inside the larger conversion chain, see our entries on the LLC resonant converter that usually follows the PFC stage and on synchronous rectification on the low-voltage output.
In Simple Terms
Power Factor Correction (PFC) is the front-end circuitry inside a switch-mode power supply that forces the current drawn from the AC line to track the…