Characteristics and working methods of PFC regulated switching power supply

　　In the PFC switching power supply, the switching regulated power supply is a very important part. The difference between the function of the switching regulated power supply in the PFC and the ordinary switching regulated power supply is not huge, but it is different in the power supply. Ordinary switching regulated power supply requires 220V rectifier power supply, while PFC regulated switching power supply is powered by B+PFC.

　　After rectification, no filter capacitor is added, and the unfiltered pulsating positive half-cycle voltage is used as the power supply of the chopper. Because of the chopper's series of "switching" work, the pulsating positive voltage is "chopped" into a current waveform, and its waveform The features are:

　　1. The current waveform is intermittent, its envelope and voltage waveform are the same, and the envelope and voltage waveform are in phase.

　　2. Due to the action of chopping, the half-wave pulsating DC power becomes high-frequency (determined by the chopping frequency, about 100KHz) "AC" power. The high-frequency "AC" power needs to be rectified again before it can be stabilized by the subsequent PWM switch. voltage power supply.

　　3. From the perspective of external power supply, the power system achieves the same phase of AC voltage and AC current, and the voltage waveform and current waveform conform to the sinusoidal waveform, which not only solves the problem of power factor compensation, but also solves electromagnetic compatibility (EMC) and electromagnetic interference (EMC). EMI) problem.

　　The high-frequency "AC" power is rectified by a rectifier diode and filtered into a DC voltage (power supply) to supply power to the PWM switching power supply of the subsequent stage. This DC voltage is called: B+PFC in some materials (this is the case with TPW-4211). The B+PFC voltage output by the chopper is generally higher than the +300V after the original 220 AC rectification and filtering. The reason High voltage is selected, and its inductance has a small wire diameter, a small line voltage drop, a small filter capacitor capacity, and a good filtering effect.

　　At present, in the PFC switching power supply part, the chopper tube (K) that plays the role of switching has two working modes:

　　1. Continuous conduction mode (CCM): The operating frequency of the switching tube is constant, and the duty cycle (coefficient) of the conduction changes with the amplitude of the chopped voltage. 2. Discontinuous conduction mode (DCM): The operating frequency of the chopper switch varies with the size of the chopped voltage (the "on" and "off" times are equal in each switching cycle).

　　The PFC switching power supply part and the excitation part of the PWM switching power supply part in the power factor correction switching power supply are all completed by one integrated circuit, and one IC can complete the design.

　　The above is a brief introduction of switching regulated power supply PFC. It can be seen that this switching regulated power supply has the characteristics of small inductance path, small line voltage drop, and small filter capacitor capacity. Compared with the traditional switching regulated power supply, it has obvious advantages.

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