There are some problems with the PFC circuit power-on process. Please consult

西里古1992

There are some problems with the PFC circuit power-on process. Please consult [Copy link]

1. In the power-on startup waveform below, the AC input current Iac has two oscillations with short periods before the LLC circuit works. What's going on?

From my understanding of the first paragraph, it is caused by the power supply charging the BUS capacitor at the moment of power-on, is that right?

The second section captures more waveforms, including the Vds waveform of the PFC-MOS tube and the waveform of the safety relay in the input circuit. Is it the changes in these two places that cause the input current Iac to oscillate?

The pin of RE010-C1 here is RLY-DR. When the level is low, the relay is closed. Looking at the waveform, it seems that the safety relay is turned on first, then disconnected, and then turned on again?

qwqwqw2088

If you suspect that the power supply charges the BUS capacitor at the moment of power-on, disconnect the USB first to verify.

qwqwqw2088

The information provided by the OP is: PFC circuit, LLC circuit, control relay, USB charging,

The circuit given is a piece of...

Several specific points of waveform measurement

西里古1992

qwqwqw2088 posted on 2022-8-3 08:24 The information provided by the OP is PFC circuit, LLC circuit, control relay, USB charging, and the circuit provided is a... The waveforms are specifically measured...

What are the specific waveforms? They are marked in the picture. They are the origins of the two oscillations of different Iac.

qwqwqw2088

Sirigu 1992 posted on 2022-8-15 15:35 Which waveforms are they? They are marked in the picture. This is the origin of the two oscillations of different Iac

How do you determine that "the waveform feels like the safety relay is turned on, then off, and then on again"?

It is recommended to take a screenshot of a slightly larger circuit.

西里古1992

qwqwqw2088 posted on 2022-8-15 15:59 How do you judge that "the waveform feels like the safety relay is turned on first, then off, and then on again"? It is recommended to take a screenshot of a slightly larger circuit...

西里古1992

qwqwqw2088 posted on 2022-8-15 15:59 How do you judge that "the waveform feels like the safety relay is turned on first, then off, and then on again"? It is recommended to take a screenshot of a slightly larger circuit...

I sent the simplified diagrams of the input circuit and PFC circuit. I am mainly wondering why the PFC bus voltage boost waveform is divided into two sections, and why the input current Iac oscillates every time it is boosted.

qwqwqw2088

Sirigu1992 posted on 2022-8-15 18:05 I sent the simplified diagrams of the input circuit and PFC circuit. I am mainly wondering why the PFC bus voltage boost waveform is divided into two sections, and the input current Ia ...

From the simplified circuit diagram,
the so-called two-period oscillation with not too long a period may be caused by the start and stop of the PWM waveform, which can be ignored.

However, I suspect that other factors, such as the load size of the relay, may cause this. I need to check the working waveform of the relay during this period based on the waveform, that is, what state the relay is in during these two stages, or other actions caused by the input current Iac.