jwhitmore
Posts: 40
Joined: Mon Oct 01, 2012 5:32 pm

Back Powering the Pi via the GPIO Header?

Sun Sep 30, 2018 11:28 am

Looking at designing a HAT which will supply 5V power to the RPi. As a result I'm looking at the notes on back powering [1] and specifically the link to the back powering diagram. That diagram just show that I need a protection diode in the HAT design, but isn't too specific about the type of diode or any specification for that diode. I'm not an expert but I've seen where people use MOSFET instead of Diodes because of the much reduced voltage drop in the protection circuit. Could that design be used or should a diode, (Schottky?) be used?

[1] https://github.com/raspberrypi/hats/blo ... pio-header
[2] https://github.com/raspberrypi/hats/blo ... iagram.png

aBUGSworstnightmare
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Re: Back Powering the Pi via the GPIO Header?

Sun Sep 30, 2018 5:33 pm

If you want a diode use a Shottky as they have low voltage drop.

Also made some add-on boards which power RPi with 5V via GPIO; no diode or protection circuit used

jwhitmore
Posts: 40
Joined: Mon Oct 01, 2012 5:32 pm

Re: Back Powering the Pi via the GPIO Header?

Wed Oct 03, 2018 12:32 pm

Thank you for that clarification. Busy designing ;)

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mahjongg
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Re: Back Powering the Pi via the GPIO Header?

Wed Oct 03, 2018 2:54 pm

Schottky diode will still cause too much drop, ideally you will need a "perfect diode", such as the one used in the PI3B to prevent backpowering the microUSB PSU, the schematic of it is shown in the abbreviated schematic of the 3B here: https://www.raspberrypi.org/documentati ... educed.pdf. consisting of Q3, U14 and R2 and R3

You should also add a polyfuse if you power through the GPIO Header.

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Imperf3kt
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Re: Back Powering the Pi via the GPIO Header?

Wed Oct 03, 2018 8:00 pm

I recently stopped powering via the GPIO header as I had been for several months, and instead started using PP1 and the underside of pin 6. Using this configuration allows me to bypass the micro USB port, but still have the polyfuse.

Maybe that is an option? (it voids your warranty though, since you must solder directly to the board)
Stop plugging your fan directly into the GPIO 5v
https://www.electronics-tutorials.ws/power/transient-suppression.html

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