Author Topic: MOSFET reverse polarity protection  (Read 525 times)

benny_profane

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MOSFET reverse polarity protection
« 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?

« Last Edit: October 09, 2020, 08:47:00 AM by benny_profane »

TFZ

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Re: MOSFET reverse polarity protection
« Reply #1 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...

benny_profane

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Re: MOSFET reverse polarity protection
« Reply #2 on: October 09, 2020, 01:15:05 PM »
Thanks for verifying that. I'll send a message to DEFX.

PMowdes2

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Re: MOSFET reverse polarity protection
« Reply #3 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.
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benny_profane

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Re: MOSFET reverse polarity protection
« Reply #4 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.