Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

MOSFET Reverse Conduction

Status
Not open for further replies.

dknguyen

Well-Known Member
Most Helpful Member
hi. Simple question that I can't seem to find an answer for. We all know the body diode in an NMOS only lets it block current in from drain to source when Vgs<Vt. If current tries to flow from source to drain in this state, the body diode will allow current to pass causing the diode voltage to appear across the MOSFET source-drain terminals.

My question is if this is occuring, and you suddenly apply Vgs across the MOSFET terminals, does it have no effect? ie. the voltage across drain-source is still the diode forward voltage. Or does it improve the NMOS's ability to pass current from source-drain beyond that of the body diode (ie.the NMOS behave like a resistor like if it was passing current from drain-source)?

THanks.
 
Logic level/lateral mosfets are completely symmetric. Power/vertical mosfets have asymmetric doping on the source and drain, so I think the gain/threshold voltages will be different, but it definitely will turn on.
 
Turning on the MOSFET in reverse is an excellent way to reduce losses instead of letting the diode do the work. I've used it to improve the efficiency of one particular circuit from an original 65% to almost 90%.
 
THat's what I was looking for. Thanks. It's more for getting rid of replacing the diode forward voltage offset with the negligble MOSFET source-drain voltage offset for back EMF measurement in my case.
 
This sort of thing is often done to protect circuits from reverse polarity because it has the advantage of having virtually no voltage drop.
 
synchronous regulators use this method to increase efficiency from their standard counterparts. for instance, in a buck regulator, the diode is replaced with a FET. For the time duration between the upper fet turning off and the lower fet turning on, the lower fet body diode (or sometimes an external schottky) will be forward biased but once the lower fet is on, conduction through the diode ceases and the current flows across the Rds(on) of the fet.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top