MOSFET h-bridge

[robotjosh]

Hello all,

 

I am a student and trying to design a medium power h-bridge, and this question has me stumped.

 

If using synchronous rectification, how do the recirculation FETs conduct? The attached image shows how synchronous rectification is done in an h-bridge. The problem is, 3-lead FETs are designed to conduct positive current drain-to-source only. But during the off PWM cycle, when current is recirculating through the motor, one FET is always conducting source-to-drain. Is this possible? It seems to be a common way to brake a motor, turning both high or low side FETs on. When turned on, can FETs actually conduct positive current source-to-drain though the FET element and not the body diode?

 

Thanks in advance,

 

Josh