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This dev board, forgive my second question on it today.

My question is regarding the Schottky diode. It looks to me like the USB 5V is wired to the cathode. Wouldn't that mean it would only allow reverse current in the micro-amp range through? I would've expected the diode the other way around, to prevent back-feeding the host port.

Edit: Here is another schematic, seemingly of one of a million knockoffs, with the schottky the other way around. Seems to be a schematic error in the Digistump schematic.

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As it is now, it prevents back-feeding the 5V to PC.

Whether that is the intention or not, is unknown. Most likely it is an error in the schematic as that device is supposed to be USB-powered.

That circuit also pulls the USB data line to 5V, and uses 5V MCU and zener diodes ro clamp voltages to 3.3V.

If anything in that circuit fails, it will destroy an USB port, so don't plug it into your only or most expensive PC, rather get a device with real USB interface.

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  • \$\begingroup\$ But if it's only plugged into USB, with no external power, would it be powered as drawn? \$\endgroup\$ Commented Feb 2, 2021 at 13:22
  • \$\begingroup\$ If I recall, the schematic simply has an error, and the picture of the actual board has the diode mounted correctly, so it will power up when plugged to PC. \$\endgroup\$
    – Justme
    Commented Feb 2, 2021 at 14:30
  • \$\begingroup\$ That would make sense. Thanks for your help! \$\endgroup\$ Commented Feb 2, 2021 at 15:15

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