Introduction
Power Factor Correction (PFC) is a technique used to improve the efficiency of electrical power usage. It increases the ratio of real power (the power actually consumed by the device) to apparent power (the total power supplied by the utility).
In power supplies without PFC, the power factor typically ranges from 0.4 to 0.6. When a PFC circuit is added, the power factor can improve to 0.95 or higher, significantly enhancing energy utilization.
Understanding Power Factor
The key formulas related to power factor are:
- Apparent Power (VA) = Input Voltage × Input Current
- Real Power (W) = Input Voltage × Input Current × Power Factor
A low power factor means more current is required to deliver the same amount of real power. This increases the load on power plants and the electrical grid.
Why PFC Matters: Energy Efficiency & Environmental Impact
Power plants must generate power based on apparent power.
Example:
- If power factor = 0.5, the power plant must generate more than 2VA to supply 1W of real usable power.
- If power factor = 0.95, the power plant only needs to generate about 1.06VA to deliver 1W of real power.
This shows why PFC is crucial — it reduces wasted power, lowers infrastructure burden, and supports global energy-saving efforts.
Types of Active PFC Topologies
Active PFC is commonly implemented using two topologies:
1. Single-Stage Active PFC
Advantages
- Lower cost
- Simple circuit design
- High efficiency in low-power applications
Disadvantages
- Large output ripple
- More complex feedback control
Limitations
- No hold-up time: Output is affected directly by AC input fluctuations
- High ripple current: Can shorten LED lifespan when driving LEDs directly
- Poor dynamic response: Performance may change significantly with load variations
2. Two-Stage Active PFC
Advantages
- High efficiency
- Higher and more stable power factor
- Easier feedback control
- Better adaptability to changing load conditions
- Suitable for all kinds use
Disadvantages
- Higher cost
- More complex circuit design
Summary
PFC is essential in modern power electronics for improving energy efficiency, easing the load on power grids, and supporting environmentally friendly operation. While single-stage PFC is cost-effective for small wattage devices, two-stage PFC provides better stability and performance for demanding applications.
