kfox1111
Posts: 1
Joined: Sat Jul 13, 2019 10:35 pm

usb and direct power

Mon Jul 15, 2019 4:09 pm

I have a raspberry pi 4. I'd like to use the usb-c connector to do usb gadgets. I'd also like to power the board directly. In this configuration though, power could be obtained from the usb-c port at the same time as the direct power feed, potentially causing problems. Is there a way to ensure power is never drawn from the usb-c port?

drgeoff
Posts: 9744
Joined: Wed Jan 25, 2012 6:39 pm

Re: usb and direct power

Mon Jul 15, 2019 6:06 pm

kfox1111 wrote:
Mon Jul 15, 2019 4:09 pm
I have a raspberry pi 4. I'd like to use the usb-c connector to do usb gadgets. I'd also like to power the board directly. In this configuration though, power could be obtained from the usb-c port at the same time as the direct power feed, potentially causing problems. Is there a way to ensure power is never drawn from the usb-c port?
The way to ensure a RPi4B never draws power from the USB-C port is to not connect said port to power.

There is no software control of where the board takes power from. The power pins of the USB-C socket are hard wired to the power pins of the GPIO header.

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thagrol
Posts: 1777
Joined: Fri Jan 13, 2012 4:41 pm
Location: Darkest Somerset, UK
Contact: Website

Re: usb and direct power

Mon Jul 15, 2019 9:50 pm

What drgeoff said.

However I currently have a 4B and 1B connected via the 4B's USB C port and both are being powered via their GPIO headers.

Probably not ideal if each have their own PSU (differing ground levels, output voltage variences etc) but in my case both Pi are bieng powered by the same ATX PSU and both on the same 5v rail.

Not yet seen any problems but I'm still planning to power the 1B just via the USB C connection. Need to migrate it to a read only root first.

As always, what works for me may not work for you and "use at your own risk"

The safest approach would be to cut the +ve power line in the cable between the 4B and the USB host.
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