Operation Manual

29
Q. What is the layman’s explanation of Power Factor Correction (PFC)?
A. The Power Factor is a measure of the real power available. It is the ratio
of real power to apparent power. It is a number which can vary from 0 to
1.0. The lower the number, the lower the real power. Poor power factor has
two causes: phase difference between AC voltage and current as found
in heavy industries mainly due to inductive loads (ex. motors) and current
waveform distortion as found in electronics equipment.
In power supplies without PFC, current can only flow at the peak of AC
voltage crests and these peaks can be huge. In power supplies employing
PFC current flows continuously and in the same shape as the voltage.
To elaborate, power supplies without PFC draw the AC input current in
short bursts or spikes relative to the line voltage, as shown in Fig. 1.
POWER FACTOR CORRECTION IN SUB 2
Fig. 1: Input of power supplies
without PFC. The voltage waveform
is a sine wave and the current
waveform is a pulse or spike.