Brief description of what is PFC regulated switching power supply

Among PFC switching power supplies, switching power supplies are a very important part. The difference between the switching regulator power supply function in PFC and the ordinary switching regulator power supply is not huge, but it is different in power supply. The ordinary switching power supply requires 220V rectification power supply, while the PFC regulated switching power supply is powered by B+PFC. This article will briefly introduce the PFC power supply.

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

1. The current waveform is intermittent, the envelope and voltage waveforms are the same, and the envelope and voltage waveforms 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 must be rectified again to be stabilized by the latter stage PWM switch. Press the power supply.

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

The high-frequency "AC" power is rectified by a rectifier diode and filtered to become a DC voltage (power supply) to the PWM switching power supply of the subsequent stage. The DC voltage is referred to as B+PFC (as is the case with TPW-4211). The B+PFC voltage at the chopper output is generally higher than the +300V after the original 220 AC rectification filter. The reason is that high voltage is used. The inductance has a small wire diameter, a small line voltage drop, a small filter capacitor capacity, a good filtering effect, and low requirements for the latter stage PWM switching tube.

At present, the PFC switching power supply part, the chopper tube (K) that functions as a switch has two working modes:

1. Continuous conduction mode (CCM): The operating frequency of the switching transistor is constant, and the duty cycle (coefficient) of the conduction changes with the amplitude of the chopping voltage.

2. Discontinuous conduction mode (DCM): The operating frequency of the chopper switching tube varies with the magnitude of the chopping voltage (the "on" and "off" times are equal in each switching cycle).

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

The above is a brief introduction of the switching regulator power supply PFC. It can be seen that the switching regulator power supply has the characteristics of small inductance path, small line voltage drop, and small filter capacitor capacity. Compared with the traditional switching power supply, it has obvious advantages. Friends who still don't understand PFC switching power supply can spend a few minutes reading this article, I believe there will be unexpected gains.