The function of switching power supply PFC circuit

PFC’S full name is “Factor Correction Power”, which means “power factor correction”. The power factor refers to the relationship between the effective power and the total power consumption (apparent power). The power factor can be used to measure the power of the electric power, and when the power factor is higher, the higher the power utilization ratio is. With PFC switching power supply costs are relatively high.
Switching power supply is a kind of capacitor input circuit, the phase difference between the current and voltage can cause the loss of the switching power, which requires the PFC circuit to improve the power factor. At present, there are two kinds of PFC, passive PFC (also known as passive PFC) and active PFC (also known as PFC).
Passive PFC is generally divided into “Valley” and “Fill Circuit”. The phase difference between the fundamental current and the voltage of the AC input is reduced to improve the power factor, and the passive PFC includes the silent type passive PFC and passive passive PFC. The power factor of the passive PFC can only reach 0.7 ~ 0.8, it is generally in the vicinity of the high voltage filter capacitor.
The valley fill circuit belongs to a new type of passive power factor correction circuit and its characteristics is the rectifier bridge behind the valley fill circuit to greatly increase rectifier conduction angle, through filled Valley, the current input from spike pulse becomes close to sinusoidal waveform, power factor is increased to 0.9%, significantly reduce the total harmonic distortion. Compared with the traditional passive power factor correction circuit, the circuit is simple, the power factor compensation is remarkable, and it is not required to use the large size of the large weight of the input circuit.
The active PFC is composed of the inductor capacitor and electronic components, small size, through the special IC to adjust the current waveform, the phase difference between the current and voltage compensation. Active PFC can achieve high power factor, which is usually more than 98%, but the cost is relatively high. In addition, the active PFC can also be used as auxiliary power supply, so in the use of active PFC circuit, it is often not necessary to standby transformer, and active PFC output DC voltage ripple is very small, this power does not need to use a large capacity of filter capacitor

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