Strange USB power behaviour

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WilliamJones

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Aug 19, 2018
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I experienced something that I have not seen before. I have a desktop with Win10. I have a small tally light that is plugged into the computer's USB for power. The computer has USB 2.0 and the tally light uses a USB-C connector. When I shut down the computer, the light stays lit. If I want the light to shut down, I pull the USB connector out of the computer. The next day, before I turned on the computer, I plugged the USB into the computer and the light turned on. I expected the light to go out when the computer is off. Is this normal? If so, what is happening here?
 
It depends on the computer. Some will keep power on one or more USB ports to allow for wake on keyboard/mouse functionality when the rest of the system is powered down. Sometimes there’s a firmware option to disable it.
 
I've just put together a (mostly) new computer with an MSI B550 Gaming Carbon Wifi board, and it has this behavior, which is rather annoying, as I'd rather not need to buy a usb hub with power buttons or unplug the device repeatedly. I was unable to find any options in the bios that seemed to be related. Does anyone know of a bios setting on that board to shut-down the USB power behavior for when the computer is off?
 
sover said:
I've just put together a (mostly) new computer with an MSI B550 Gaming Carbon Wifi board, and it has this behavior, which is rather annoying, as I'd rather not need to buy a usb hub with power buttons or unplug the device repeatedly. I was unable to find any options in the bios that seemed to be related. Does anyone know of a bios setting on that board to shut-down the USB power behavior for when the computer is off?
Click to expand...

Look for something about EU ErP. With that enabled, standby power is supposed to be limited to 0.5w, which might mean they turn off USB (or at least some of the ports). On my recent builds it will turn off wake-on-lan if set.
 
Look for power pass though in the bios, you should be able to disable if needed or at least determine what ports are always on.
 
Yep, USB power when PC powered down can be disabled in the bios.
 
toast0 said:
Look for something about EU ErP. With that enabled, standby power is supposed to be limited to 0.5w, which might mean they turn off USB (or at least some of the ports). On my recent builds it will turn off wake-on-lan if set.
Click to expand...

robijito123 said:
Look for power pass though in the bios, you should be able to disable if needed or at least determine what ports are always on.
Click to expand...

Thanks for the pointers, I'll check for these things!
 
Oh, I almost forgot to come back and let you guys know what my resolution was. I already had the ErP thing enabled, and there wasn't anything labeled as power pass through, but I did a lot of experimenting and it appears that there is a page in the MSI bios (for the carbon gaming b550 wifi, at least) that either places the bios in command of wake events, or passes the responsibility to the OS. It was set to bios previously, but after changing that setting from bios to OS the USB power seems to go off completely with the computer is shut down.
 
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