PFC Revealed!

As you all know, AC power is a power source with alternating voltage and current. For AC power to be useful, the voltage and current must be in the same phase. If there is misalignment of the phase angle of the AC voltage and current's sine waves, then it must be corrected before the AC power can be used.

In Non-PFC power supplies, a capacitive filter that consists of capacitors is used to rectify the phase misalignments. However, such filters cause very high current flow at the peak of every AC sine wave crest. This current surge causes a sudden voltage drop in the power supply's AC source and disturbs the power company's AC line.

This reduces the energy potential of the AC line. In other words, the percentage of usable AC power that can be provided by the power company's AC line is effectively reduced. This is why PFC is so important to the power company. Hence, the new EU regulation making PFC mandatory in all home appliances consuming power of 70W or more.

The high peak currents also increase the amount of EMI (Electromagnetic Interference) and RFI (Radio Frequency Interference) produced by the power supply. The power supplies we use today are actually switching power supplies that discharge power 50 to 100 thousand times a second to the computer. Such rapid switching by itself creates a lot of EMI and RFI. Add in the high peak currents from the AC source and you will have greatly increased EMI and RFI.

For the consumer, the increased EMI and RFI are usually no more than a nuisance, and then only when an electrical or electronic appliance is affected. But the EMI and RFI also affect the AC line and the noise has to be dissipated by the power company. It is not something they enjoy doing.

This is where PFC comes in. PFC is the method by which the high peak current and harmonics on the output voltage are reduced. The advantages of PFC are reduced EMI/RFI and a cleaner AC line with increased energy potential, both of which are far more advantageous to power companies than the consumer.

With that said, the future lies with PFC. There is no denying that increased efficiency should be the goal, even if there is little benefit as such to the consumer.

PFC Types

There are two types of Power Factor Correction - Passive PFC and Active PFC.

Passive PFC uses passive elements like a ferrite core inductor on the AC input. It is very easy to implement in existing power circuits although the power factor is low at 60-80%. The proper AC input voltage (115V or 230V) must also be chosen manually. In addition, significant EMI can still result with a 115V AC source. Of course, a 230V AC source will not have this problem!

Active PFC, on the other hand, uses a switching regulator with active elements like an IC, FETs (Field Effect Transistors) and diodes to create an active PFC circuit. This circuit allows the power supply to achieve a power factor of up to 95%, significantly reduce harmonics and automatically adjusts the AC input voltage. This means you do not have to manually select the AC input voltage. It works with all voltages from 110V to 240V.