ZVS in PFC circuit

[ivan_mateo]

Hi everyone,

I am plannig to design a constant on time and vary frequency pfc circuit. I found some equations but could not understand how to zvvs is achived in that circuit. ınductor current ramp up at on time, and when the inductor current is decreased at off time. But off time is continue because current is negative and ton is delayed. Can anybody expalin how these theory expain with below equations?

 

[treez]

Boost PFC in transition mode will not usually zvs. The drain node will ring up and down after the inductor completely discharges. It will ring down to a voltage of vin - (vout-vin). As you know, the drain voltage will not go negative by any more than a diode drop.

And as you know, "Vin" is the bus voltage after the mains rectifier, which changes sinusoidally in a boost pfc.