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MOSFET reverse polarity protection

Started by benny_profane, October 09, 2020, 01:54:08 PM

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benny_profane

I'm working on a Laika V2 from DeadEnd FX. This circuit uses a MOSFET for reverse polarity protection. I wanted to get a quick sanity check because it seems like the MOSFET is oriented backward. Shouldn't the V+ input go to the drain of a p-channel MOSFET with source going to the circuit? Also, could this be improved with a gate-to-source protection (9.1V) zener?


TFZ

Yes, drain and source are wrong in the schematic. Protection diode: never used one. BS250 has +-25VGS, the MOSFET I use has +-20V. So far no problems...

benny_profane

Thanks for verifying that. I'll send a message to DEFX.

PMowdes2

Looks like I drew the symbol upside down in my Eagle library, the pads and orientation are correct on the pcb.
DeadEndFX

benny_profane

Great, thanks!

As an aside, why isn't this method of polarity protection used more often? Is it due to cost and the extra components? It's more efficient and less destructive than diode-based solutions.