Quick question on synchronous rectifying

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achilez

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Ultimately, my goal is to design a synchronous buck converter (from scratch), but I'm thinking I should try the simplest solution first -- i.e., with a rectifying diode.

Are there any reasons I could not make a design with the (future) sync mosfet already on the pcb, albeit shorted out by a rectifying diode, and later when I see that everything works as it should I can simply remove the diode, and connect the mosfet to a driver?

I'm not sure what I'm worried about.. maybe if the parasitic capacitances etc would somehow interfere... eh?

Thanks.
 

Hi,

You have to take care on your High side and Low side driver signals. Make sure that their ON time don not overlap as it may lower your power efficiency.

I suggest you straightly design a sync buck. you can always add the rectifier diode.

Regards.
 

Thanks. So, you're saying the a N-MOSFET will just sit there doing nothing (while the rectifying diode is busy at work) until I decide to hook up its gate to a driver signal?

Also, are there any other issues down the road concerning synchronous rectifying? I've looked around, and from what I've read it seems like a pretty straight forward measure to take for a relatively large increase in efficiency (for my low-voltage app). Just insert some drive signal dead-time to avoid shoot-trough, and we're good to go?
 

The FET will act as a diode in its own right (D-{B+S} junction)
but you may not like the recovery / storage time and see
switching losses from that. A back Schottky would keep the
current from lighting the sync rect FET up.
 

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