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Projects => General Questions => Topic started by: benny_profane on October 09, 2020, 07:54:08 AM

Title: MOSFET reverse polarity protection
Post by: benny_profane on October 09, 2020, 07:54:08 AM
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?

Title: Re: MOSFET reverse polarity protection
Post by: TFZ on October 09, 2020, 01:07:06 PM
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...
Title: Re: MOSFET reverse polarity protection
Post by: benny_profane on October 09, 2020, 01:15:05 PM
Thanks for verifying that. I'll send a message to DEFX.
Title: Re: MOSFET reverse polarity protection
Post by: PMowdes2 on October 10, 2020, 03:27:22 AM
Looks like I drew the symbol upside down in my Eagle library, the pads and orientation are correct on the pcb.
Title: Re: MOSFET reverse polarity protection
Post by: benny_profane on October 10, 2020, 10:03:46 AM
Great, thanks!

As an aside, why isnít this method of polarity protection used more often? Is it due to cost and the extra components? Itís more efficient and less destructive than diode-based solutions.