tryingtolearn
Posts: 19
Joined: Sun Feb 26, 2017 1:56 am

Ideal Diode Question (Pwr from a hat)

Fri Sep 24, 2021 4:34 pm

I am setting up the circuit from this diagram
https://github.com/raspberrypi/hats/blo ... ircuit.png to power the pi from a board ("Hat")

Is the basic concept that if someone inadvertently plugs in the pi power while the power is already attached through the "Hat" that it will just use the higher of the two??

so for testing I set the bench power supply to 4.7v and booted the pi from the hat
read just a little under 4.7 at the Drain of the DMG2305UX
Then used a pi power supply and plugged it in through the pi power port while the bench supply still attached
The drain went up to 5.1

IS that attached ideal circuit functioning properly in that case?

THanks for any info.

emma1997
Posts: 1646
Joined: Sun Nov 08, 2015 7:00 pm
Location: New England (not that old one)

Re: Ideal Diode Question (Pwr from a hat)

Fri Sep 24, 2021 5:59 pm

If it is indeed selecting the higher of the two then does seem to be working. I have used that exact same circuit but not with Pi hats. For poor man's UPS I found regular Schottky diodes do the job of selecting between two supplies and infinitely easier to implement. Assuming the tenth of a volt or so drop is ok. With adjustable PSU or DC-DC this is of course not an issue.

tryingtolearn
Posts: 19
Joined: Sun Feb 26, 2017 1:56 am

Re: Ideal Diode Question (Pwr from a hat)

Fri Sep 24, 2021 6:14 pm

Thanks for responding.
Wanted to double check before moving on. I appreciate it.

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