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Switch-off switching loss in Active Clamp Forward converter?

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treez

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Page 7 (LHS) of the following (below) article is totally wrong, do you agree?

It says that regarding active clamp forward converters, “With sufficiently fast gate drive,
the turn off of Q1 can be virtually lossless.” (Q1 being the main power mosfet).

This is impossible, current cannot suddenly go to zero in Q1 and cannot immediately divert into the clamp capacitor until the drain voltage has risen to V(clamp) + V(diode).
So do you agree that this article is totally wrong in saying that there are no turn off switching losses in the main power fet?


https://www.ti.com/lit/an/snva591/snva591.pdf
 

Yeah it doesn't sound convincing to me. The key phrase they use is:
The rise of the drain voltage is delayed due to the drain-source capacitance; a robust gate driver can turn off Q1 before the drain voltage increases significantly.
Click to expand...
So basically they're saying that if your Cds is huge, you can avoid overlap in Vds and Ids simply. Obviously this is true, but this has nothing to do with the active clamp mechanism. And the extra energy in that large Cds will just be dissipated during Q1 turn-on instead, so it may not matter overall. But this sort of switching loss reduction can be achieved using slew-rate limiting regenerative snubber circuits.
 
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