ZVS in the forward converter

[rajeshwari14]

hi ,
can anybody explain ,how the ZVS is achieved during turn off in the attached paper

 

[mtwieg]

It's ZVS in the sense that when S1 and S2 are turned off, their Vds rises due to freewheeling current charging their drain capacitances C1/C2, until the diodes start clamping to Vin. This is technically ZVS, because the no energy is wasted in charging C1 and C2 (as it would be if the diodes D1 and D2 were hard switched on).

But in this sense, every type of non-synchronous converter circuit has ZVS turn off.

 

[rajeshwari14]

hi
Thanks a lot for the reply.
I
For the Circuit shown in the paper I am able to get ZCS during turn on but not able to get ZVS during turn off ? Can you please tell me the reason and remedy for it .

 

[mtwieg]

How are you evaluating whether you have Zvs turn off? As I said above, for that circuit ZVS turn off is basically guaranteed by design.

 

[rajeshwari14]

hi
sorry, ZVS is still not clear to me.
In my simulation result, i was expecting zero current and zero voltage at the instant of turn off.I thought that is the meaning of ZVS.
But,In my simulation during turn off,vds increases upto vin and then the current starts to fall.
Am i getting right result?