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why is it always that a P-Channel MOSFET is used with reverse polarity protection?

Can we just use an N-Channel MOSFET?

Analog
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  • Do you how the p channel mosfet works for reverse polarity protection ? If so, can those same attributes/ characteristics be used with an N channel ? – efox29 Jun 21 '21 at 14:38
  • I'm a beginner when it comes to MOSFETS. I have seen some videos where they use a P-Channel, but non of them explained why. Does any of this have to do with the body diode? – Analog Jun 21 '21 at 14:48
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    You can, but you'd have to put it in the GROUND line instead of the POWER line. – Kyle B Jun 21 '21 at 14:55
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    It has nothing to do with the diode. A MOSFET only cares what the relative voltage of GATE to SOURCE is. Look close at the circuits you found, consider what voltage will appear on the MOSFET. For an N channel, if the GATE is more positive than the SOURCE, it will turn ON. If not, it turns off. For a P Channel, it's opposite... If the gate is MORE NEGATIVE than the source, it turns on. – Kyle B Jun 21 '21 at 14:57
  • Relevant question: How can I add N channel MOSFET for reverse polarity protection? – ErikR Jun 21 '21 at 15:01
  • because the n-chan would drop a lot of voltage between D and S; basically the same as Vgs(th). Ex: 12v going into D+G would result in 9v coming out of S. – dandavis Jun 21 '21 at 22:25

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You can use an N-channel MOSFET for reverse polarity protection, as attested to by these SE questions:

A lot of designers like to keep the grounds of their power supply and application circuit at the same potential and using an N-channel MOSFET means you introduce an element between them. Any return ground return current will increase the separation between these two potentials.

For a battery operated device this shouldn't be an issue, but perhaps the habit remains. After all, a diode for reverse polarity protection may also be used on the high side or low side, but in designs you always see it on the high side.

ErikR
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