Motherboard PCI-E power during shutdown

MuffinDealer · February 18, 2020

Current motherboards have a setting in bios that enables USB power while system is shut down so you can power your phone without the need for cpu to consume power with running an OS.

I assume that there is some type of power management control on the motherboard that enables this.

So i'll go straight to it:

Can motherboards provide power to pci-e components while system is shut down?
Is there a setting that provides power to pci-e components?
Do pci-e devices communicate their power requirements to MB or does that communication require CPU to provide variable power draw or set stable power draw?
Would this function require just a bios update or does the motherboard need to be designed with this feature beforehand (with additional chips and pathing)?
Are there power states that would enable this without the need for the OS to be in idle?

I just can't find the answers on the web. Thanks for any info on this in advance .

ZzLy · February 18, 2020

2 minutes ago, MuffinDealer said:

Current motherboards have a setting in bios that enables USB power while system is shut down so you can power your phone without the need for cpu to consume power with running an OS.

I assume that there is some type of power management control on the motherboard that enables this.

So i'll go straight to it:

Can motherboards provide power to pci-e components while system is shut down?

Is there a setting that provides power to pci-e components?

Do pci-e devices communicate their power requirements to MB or does that communication require CPU to provide variable power draw or set stable power draw?

Would this function require just a bios update or does the motherboard need to be designed with this feature beforehand (with additional chips and pathing)?

Are there power states that would enable this without the need for the OS to be in idle?

I just can't find the answers on the web. Thanks for any info on this in advance .

Some graphics cards have a little led that indictas if the correct 6 or 8pin pcie power is plugged in, and this light stays on even when the system is off, so clearly the pcie slot is providing power to the card even when it's off.

MuffinDealer · February 18, 2020

5 hours ago, ZzLy said:

Some graphics cards have a little led that indictas if the correct 6 or 8pin pcie power is plugged in, and this light stays on even when the system is off, so clearly the pcie slot is providing power to the card even when it's off.

And motherboard RGB lighting on my ROG Strix B350-F is active while system is shut down so there is something on MB that is still active.. just can't find the info in my MB manual .

The idea is you could power something like a raspberry pi(or even multiple) through a custom board and forgo the need for power adapters.

Edited February 18, 2020 by MuffinDealer
grammar

Spotty · February 18, 2020

58 minutes ago, MuffinDealer said:

Current motherboards have a setting in bios that enables USB power while system is shut down so you can power your phone without the need for cpu to consume power with running an OS.

USB devices are able to run when the system is in standby mode (shut down but plugged in) because the power supply has a 5VSB power supply. It's a smaller power supply within the PSU that runs when the system is off. This lets you power devices through USB while the system is off as well as have RGBarf keep you awake at night.

PCIe slots communicate directly to the CPU or connect to the CPU via the Chipset. If the system is off there's nothing to communicate with.

Power wise the PCIe slot can deliver 3.3V at up to 3A (~10W) and 12V up to 5.5A (66W) for a total of 75W. Since the PSU only outputs 5V when in standby mode it's unlikely you would be able to power any PCIe devices while the system is off, unless the motherboard steps down the 5V to 3.3V, though I'm not sure if any motherboards do this. Only practical reason I could even imagine for doing this is for PCIe network cards and wanting to use Wake on LAN, so maybe it's a feature built in to some server boards, though they typically use 12V only power supplies anyway which use 12VSB and step down the voltage on the board anyway.

5VSB in power supplies is usually rated for between 10-20W, so you're not really going to be able to power most PCIe devices anyway.

TLDR; No, you can't power PCIe devices while the system is off.

36 minutes ago, MuffinDealer said:

And motherboard RGB lighting on my ROG Strix B350-F is active while system is shut down so there is something on MB that is still active.. just can't find the info in my MB manual .

I'm not familiar with Asus motherboards but there's usually an option to disable the RGBarf, or toggle the ErP setting in the power settings tab should turn it off.

37 minutes ago, MuffinDealer said:

The idea is you could power something like a raspberry pi(or even multiple) threw a custom board and forgo the need for power adapters.

Raspberry Pi isn't a PCIe device though...?

Which Raspberry Pi device is it?

Quick google shows that Raspberry Pi is powered from a micro USB connector which uses 5V 2A adapter. Could just power that with a standard phone charger as a lot of phone chargers would be around 5V 2A. Just check the rating on the label of the charger to see if they're capable of doing at last 2A.

You might be able to power it by plugging the USB cable directly in to the back of the motherboard in the USB ports but I'm not sure if they'll be able to deliver the full 2A. USB 3.1 ports should be able to handle it as I believe they're capable of up to 3A but USB 2.0 ports are only rated for something like 500mA I believe.

Plug it in to the USB ports at the back of the motherboard and see if it turns on