NMOS request

[Carl-NC]

I'm looking for a power NMOS device that does not have a body (D-S) diode. Perhaps someone makes a 4-terminal NMOS? Thanks...

 

[dknguyen]

Not possible. THe body diode is not a "feature" that is added to MOSFETs. It is is not purposely built-in. It is the result of certain connections made in the MOSFET silicon to prevent it from behaving unpredictably in certain conditions. Without it, a real MOSFET would not behave properly.

You need back to back MOSFETs, or BJTs, or IGBTs if you want to block in both directions.

 

[Speakerguy]

Like dknguyen said, it's actually in intrinsic quality of a mosfet. It's just there no matter what because of the way the silicon is built up. Some mosfet's are specially designed so that this intrinsic diode behaves better than it otherwise would (like it will handle reasonable forward current for short durations so you don't need a separate freewheeling diode), but it is always there.

If you want to limit reverse current flow through the mosfet, you can try adding a diode in series with it to block the reverse current.

 

[dknguyen]

Or an active diode made from a transistor- much more efficient than an actual diode. For some reason I always think back-to-back MOSFETs for blocking current in both directions...never actually just sticking a diode in series.

 

[Speakerguy]

I see the diode thing used all the time in solid state Tesla coil drivers. How do you use two MOSFET's to do the same?

 

[dknguyen]

**broken link removed**

But then the drive requirements are all funny. Used for solid state relays.

 

[Speakerguy]

Ah, good to know. Makes sense to use two for an SSR.