[Share] ZCS conduction and drive spike issues in PWM state

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ZCS conduction and drive spike issues in PWM state

As shown in the figure below, there is a ZCS conduction phenomenon of the switch tube in the PWM state.

If the current reverses again from t2 onwards, the current is not zero. Before the resonant current turns forward again, its working diagram is as shown in the following figure (assuming that there is current on the secondary side, DR1 and DR2 may be turned on):

Before the resonant current passes through zero, the Q2 drive pulse arrives and Q2 is turned on; but at this time, the body diode D1 of Q1 is also continuing current, so the current quickly commutates from D1 to Q2, and Q2 is turned on in ZCS.

At this time, D1 reverse recovers, generating a large reverse current spike, which will couple a very high negative spike on the drive of Q1. The following is the actual waveform tested by the rectifier module in PWM state. The red circled part in the figure is the reverse recovery current spike generated when D1 commutates to Q2. There are also positive spikes on the drive, but they are easier to suppress and the problem is not prominent.

The more effective methods are:

bruce5257

Finally understood something, thank you