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I'm developing a MIDI controller around a RPi Pico type board (docs here), which doesn't support simultaneous powering through USB and a separate supply. VBUS and VSYS are outputs if powered by USB and inputs if powered by a separate power supply.

Normally the board would not be connected using USB, so an internal supply would deliver 5V to it, but on occasion, both USB and the internal supply would be connected (such as when re-programming the board).

I'm working on a carrier board for this (which would add some MIDI interfacing as well) and I'm trying to make it safe, so I was thinking about adding a 5V Zener diode (cathode to internal power supply, anode to VBUS) so that when powered through USB no current would flow from the internal supply. Something like this:

schematic

Would this work as I imagine? Would it break if connecting USB after internal power supply is ON?

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The datasheet for the Pico has section "4.5. Powering Pico" which describes powering the board from two sources. https://datasheets.raspberrypi.com/pico/pico-datasheet.pdf

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  • \$\begingroup\$ Thanks! I was unclear on how VSYS and VBUS were connected and, in hindsight, I should've looked over my specific board's schematics (which seems to mimic the basic RPi implementation, with the addition of a battery charger circuit). This makes things clear! \$\endgroup\$ Commented Aug 18, 2024 at 9:05

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