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I looking at the Raspberry Pi schematic (Rev 3b) and found this interesting section:

Rsapi3 B

The black box is described as a diode. My understanding is that this block should perform as a diode with near zero forward voltage, but I don't fully understand how it works and what to call it.

JRE
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M lab
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  • Does this answer your question? [Understanding an 'ideal' diode made from a p-channel MOSFET and PNP transistors](https://electronics.stackexchange.com/questions/223935/understanding-an-ideal-diode-made-from-a-p-channel-mosfet-and-pnp-transistors) Additional analysis [here](https://electronics.stackexchange.com/q/446246/11683). – Dave Tweed Oct 09 '21 at 12:52
  • I was just going to write an answer, thanks for the link. This is basically a reverse-polarity protection. – PMF Oct 09 '21 at 12:57
  • @DaveTweed Yes, I think about ideal diode before but mostly, it use opamp. – M lab Oct 09 '21 at 13:30
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    @PMF: No, it isn't about polarity protection at all. It's about blocking an external power supply connected on the right from back-driving the USB power, while having minimal forward voltage drop when using USB power. – Dave Tweed Oct 09 '21 at 14:25
  • it would probably also provide reverse polarity protection up-to 5V but that's not its design purpose. – Jasen Слава Україні Oct 10 '21 at 06:02

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