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Working Principle and Control Method of PFC PDF Print E-mail

PFC is not a new concept already, and it is to be used more in the UPS power supply, but rarely seen on the PC power PFC circuit. PFC rises in the PC power supply, mainly from the CCC, all necessary computer powers which need to be CCC-certified must increase the PFC circuit.

  PFC means the "reactive power factor correction", electronic products mainly used to characterize the efficiency of energy used. The higher power factor indicates that the higher the consumed energy efficiency will be.

  Using the traditional PC power supply bridge rectifier, capacitor filter circuit will have a serious AC input current waveform distortion, pouring grid into a large number of high harmonics, so the power factor on the network side is not high, only about 0.6, and the grid and other electrical equipment will be caused serious harmonic pollution and interferences. Back in the early 80s, high attention was paid by people on the caused harm of the harmonic current generated by such devices. In 1982, the International Electrotechnical Commission has developed IEC55-2 high harmonics of the specification limits (later revised specification is IEC1000-3-2), prompted a large number of power electronics technology workers began to research harmonic filter and power factor correction ( PFC) Technology. The introduction of PFC circuits into electronic power products can greatly improve energy use efficiency.

  There are two types of PFC, one is passive PFC (also known as Passive PFC), one is active PFC (also known as Active PFC). Passive PFC inductor compensation method commonly is used to improve power factor by making the AC input phase difference  decreased between the fundamental current and voltage, but the passive PFC power factor will not be very high, only reach 0.7 to 0.8; Active PFC by the LC components and electronic components, small size, can achieve a high power factor, but the cost will be much higher than passive PFC.

  Active PFC circuit often highly uses integrated IC. The PC power supplies with active PFC circuit, at least the following features will occur:
  1) Input voltage can be from 90V to 270V;
  2) line power factor will be higher than 0.99, and has the advantages of low loss and high reliability;
  3) IC for PFC also can be used as auxiliary power, so when using the active PFC circuit, the standby transformer often will be not required; 
  4) output voltage does not change with the input voltage fluctuations, so the power supply can obtain highly stable output voltage;
  5) Active PFC output DC voltage ripple is small, and it will be the sine wave showed 100Hz/120Hz (2 times the frequency), so the power supplies with active PFC do not need filter capacitor with large capacity.        
PFC circuit is used seldom on the current market, and the use of active PFC circuit is less.

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