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This seems like a very basic problem but I cannot really find a solution or come up with one on my own. The setup is simple (also picture for clarity):

  • A circuit that takes 5V input
  • Put a UPS with battery before, so it can run uninterrupted (based on this design)
  • The UPS input is 5V, either from the device's USB plug or an external power source (handled by a buck converter)
  • Any device on USB gets also powered when using the external power source

Simplified schematic of the circuit

Problem: How can I supply 5V from the UPS when on battery power without feeding back into the input of the UPS? I thought of simple diodes, but since we have 5V everywhere, that doesn't work, or not? Is there some circuit that can control the flow based on applied potentials?

This is more a bonus for the circuit, if I cannot deliver 5V during battery operation, it's okay as well.

André
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  • Does this answer your question? switch between battery and usb power no microcontroller circuit – winny Sep 14 '23 at 06:42
  • @winny If I see it correctly, this one also just switches the board supply between USB and battery power (like all others I found searching) - the UPS already handles this. I want to ensure that battery power also supplies 5V to USB, in case a not self-powered device is attached, but since it is the same line that can be used as input for the UPS, I somehow want to prevent to feed back into itself. – André Sep 14 '23 at 08:45

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