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Power supply for an microcontroller kit
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romhunter:
Hello, I'm in the process of designing a microcontroller kit (for AVR, PIC, and some chinese micros). The problem I'm facing is that I need that kit to be able to get power from either USB or an external DC power supply without something blow up. Both of those thing could be attached at the same time, and I'd prefer the external supply to power my circuitry.

Can someone suggest me an idea of what should I do?
Zero999:
If both power supplies are connected, how do you determine which one is used?

If you just want to take power from the source with the higher voltage, then an ideal diode circuit can be used.
https://docs-emea.rs-online.com/webdocs/0a82/0900766b80a826bb.pdf

If you want to select which power supply is used, based on an external input, then some additional logic (possibly another MCU) and switching (transistors or relay) is required.

Another possibility is a SPDT switch to manually select between power supplies.
romhunter:

--- Quote from: Hero999 on November 01, 2018, 10:37:41 am ---If you just want to take power from the source with the higher voltage, then an ideal diode circuit can be used.

--- End quote ---

Basically the external one range from 9-12V, got regulated down to 5/3.3V, I'd like to use it when possible. USB should only be use when external supply is unavailable
Zero999:

--- Quote from: romhunter on November 01, 2018, 10:41:09 am ---
--- Quote from: Hero999 on November 01, 2018, 10:37:41 am ---If you just want to take power from the source with the higher voltage, then an ideal diode circuit can be used.

--- End quote ---

Basically the external one range from 9-12V, got regulated down to 5/3.3V, I'd like to use it when possible. USB should only be use when external supply is unavailable

--- End quote ---
Where is it regulated down? On the board? If so, it makes it easier.
romhunter:
Yes, it will be regulated on board.
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