What is the difference between active PFC and passive PFC in power supply?

PFC: Initiative is more energy-saving.

Computer power supply is responsible for converting alternating current (AC) into direct current (DC) to provide all power for the host computer, so its energy conversion efficiency is a very important energy-saving index. The energy conversion efficiency of power supply is not necessarily related to the nominal power. It is the residual ratio of energy in the process of AC -DC conversion, and this efficiency basically depends on the power factor correction (PFC) inside the power supply.

There are two main types of PFC, one is called active PFC and the other is called passive PFC.

Active PFC itself is equivalent to a switching power supply. The control chip drives the switch tube to "modulate" the input current to synchronize it with the voltage as much as possible, and its power factor correction value can reach above 98%. Therefore, the energy conversion efficiency of power supply with active PFC circuit is above 75%, which exceeds that of ordinary passive PFC circuit. But its cost is relatively high, accounting for almost 20% to 30% of the overall cost of the whole power supply.

Passive PFC

The power factor correction value of passive PFC circuit is generally only 60% to 70%, and the energy conversion efficiency is lower than 80%.

For example, if the energy conversion efficiency of a 300W active PFC power supply is 70%, it only needs 428W AC. On the contrary, an inefficient 300W power supply, if passive PFC is used, its energy conversion efficiency is only 40%, so it needs 750W AC to output 300W DC to the computer, which wastes 322W power.

Therefore, the power supply designed by active PFC circuit must be the first choice to choose energy-saving power supply.