1 Introduction

To understand PFC, we must first define power factor. Power factor is the ratio of real power in Watts divided by the apparent power. The real power is what is consumed by the load and the apparent power is what is circulating between the source and the load. The ideal power factor is 1, meaning that there are no losses due to reactive power and all apparent power is real power. Figure 1-1 and Figure 1-2 shows waveforms of a system with a power factor of 1 and of 0.69. Note the increase in peak current due to the decreased power factor.

Switching power supplies are often used for power factor correction. Switching power supplies typically utilize a diode bridge to rectify an alternating current (AC) signal to a direct current (DC) signal. This diode bridge chops the AC signal which impacts both power factor and total harmonic distortion (THD). Filters are sometimes used for smoothing this chopped signal and improving power factor. However, these filters require large passive components and yield large power losses. Figure 1-3 shows an example of a diode bridge and a passive filtering method of PFC.