This is the reason why the current is not equal when the pfc inductor rises in the power supply design.

Many power supply designers know that PFC is an important parameter in calculating the efficiency of electrical equipment. The larger the value, the higher the utilization of electricity. Since PFC is so important, there are many related problems. This article will introduce the rise and fall current problems in the single cycle of PFC inductors, explaining why the rising and falling currents are different.

As shown in Figure 1, this waveform is continuous, and the discontinuities and criticalities are indeed equal, so why are they not equal in continuity?

The current inside the inductor is not put into 0, and it continues to charge. There is energy in the inductor. The energy inside the inductor can't reach the saturation of the inductor. The continuous mode of flyback is similar to this case. The continuous mode of BUCK and BOOST is also akin. PFC can be seen as a BOOST circuit, but there are more references.

The current of the PFC changes in proportion to the voltage. If the current rises and falls continuously, the average current waveform is not like the Sin waveform, and there is no PFC meaning.

If the PFC control circuit is to achieve such a result. Then the volt-second rule per cycle is established, is there no magnetic reset for the inductor? And if the single-switch forward converter does not work with the magnetic reset winding, will the transformer be magnetically saturated and damage the switch?

In fact, the damage of the switch tube is simply over-voltage and over-temperature. If the protection is done well, it will not damage the switch tube. The problem with magnetic saturation is that the design is unreasonable. If you think according to the limit method, the output of the secondary short circuit, the transformer sense is very small, the switch tube switch is also saturated, but the power supply will not be bad.

It can be seen from the above that the relationship between the long-rise current and the falling current of the PFC inductor cycle is still relatively complicated, which may cause a newcomer to learn from this knowledge point. But through the introduction of this article, you can understand the relationship between output and input current in detail. I hope everyone can gain something after reading this article.