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As discussed here, I'm trying to use a MOSFET for reverse polarity protection.

I got an IRFB7440PbF, which has a low Rds(On) (2mOhm,) suitable Vgs (I'm using a 5V power supply,) and what I thought would be a proper voltage drop.

I've tested it by simply connecting it between a 5V power supply and a Raspberry Pi (which would use less than 3A.) The Pi complained about low voltage. I measured 4.6V.

When reading the chart, I'm getting that the voltage drop should be 0.1V, so I should get around 4.9V:

Drain to source volage depending on drain to source current

What have I gotten wrong? Would you know any part that would meet my requirements? (5V @ 6A, dropping at most 0.2V)

JRE
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user1532080
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1 Answers1

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I'm trying to use a MOSFET for reverse polarity protection.

The IRFB7440PbF (unlike the MOSFET in your previous question) is an N channel device so it's unlikely you are able to use it for what you need: -

enter image description here

I've tested it by simply connecting it between a 5V power supply and a Raspberry Pi

The volt drop you see is probably the forward volt drop of the parasitic bulk diode inside the N channel MOSFET and not the actual MOSFET itself.

Andy aka
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