Synchronous rectifier

I don't have much experience with synchronous rectification, but lack of experience never stopped me from shooting my mouth. Get some hysteresis by using a little positive feedback on the comparator, maybe. What's this for, a SMPS?

The bane of synchronous rectifiers is dead time which occurs at light load. Select a topology that contains no dead time at light loads. cheers, Harry

Or...

If the oscillation happens right at the point where the thing is supposed to turn off, you can include a latch to hold it off.

Thank you for your reply!

I have said that the comparator is a zero-crossing detector. So it is used to compare Vds with zero, but in fact there are some offset voltage in the input of the comparator. Thus the comparator point is actually +/- several mili volts. If the comparator point is positive several milivolts, there will be a large delay when turning off the MOSFET; a negative several milivolts will cause oscillation under light/zero load. Now you may understand it is very hard to have a hysteresis for such a comparator and in fact a hyteresis here is of no use.

This is for a VRM.

Yes, I once think about adding some latch circuits, but the latch signal seems must come from the control signal of the main switch in a buck converter. I hope my chip can work alone, so a external latch signal is not a good solution. If there are any other solutions...

this article has some ideas

To Kell,

Thanks for your reply and time.

I read this article just several days ago. My integration solution is mentioned in it. And the new proposal to use a sense winding is not suit for my solution. I want to do a full integration solution. It seems that it is very hard to do like this...