In traditional switching power supplies without Power Factor Correction (PFC), the input current appears as narrow pulses near the voltage peak instead of a sinusoidal wave due to the presence of rectifier bridges and large filter capacitors. This leads to two major problems: First, a low Power Factor (PF). The current and voltage are out of phase, meaning a large amount of power is exchanged back and forth between the power grid and the load without performing useful work. Second, a high Total Harmonic Distortion (THD). The current waveform contains a large number of odd harmonics, which pollute the power grid and interfere with other electrical equipment.

Therefore, the fundamental characteristic of PFC converters is to solve these problems.

To maximize energy utilization, the regulatory requirements of most countries mandatorily stipulate that electrical appliances with an output power ≥75W shall meet a PF value ≥0.9 or higher. Especially for LED luminaire driver power supplies, a PF ≥0.9 is compulsorily required when the output power is ≥7W.

The attached document briefly introduces the working principle and inductor design of PFC converters under different operating modes, and provides engineering design examples.