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What is PFC?

 Ans:

 

Power Factor Correction or PFC is to improve the ratio of apparent power to real power. The power factor is around 0.4~0.6 in non-PFC models. In models with PFC circuit, the power factor can reach above 0.95. The calculation formulas are as follows: Apparent Power=Input Voltage x Input Current (VA), Real Power= Input Voltage x Input Current x Power Factor (W). From the point of view of environment friendly, the power plant needs to generate a power which is higher than apparent power in order to steadily provide electricity. The real usage of electricity is defined by real power. Assuming the power factor is 0.5, the power plant needs to produce more than 2WVA to satisfy 1W real power usage. On the contrary, if the power factor is 0.95, the power plant only needs to generate more than 1.06VA to provide 1W real power, It will be more effective in energy saving with PFC function.

Active PFC topologies can be divided into single-stage active PFC and two-stage active PFC, the difference is show as in the table below.

PFC topology Advantage Disadvantage Limitation
 Single-stage
 active PFC
 Low cost
 Simple schematic
 High efficiency in 
 small 
 watt application
 Huge Ripple
 complex feedback 
 control
 1.Zero “hold up time”. The output is
    affected by the AC input directly.
 2.Huge ripple current results in lower LED life
    cycle.(drive the LED directly)
 3.Low dynamic responds, easily affected by
    load.
 Two-stage active
 PFC
 High efficiency
 Higher PF
 Easy feedback control
 High adoptive against 
 load condition
 Higher cost
 Complex schematic
 Suitable for all kinds use

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