Quick question on synchronous rectifying

[achilez]

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.

 

[skowe26]

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.

 

[achilez]

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?

 

[dick_freebird]

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.