USB powered devices

  • Thread starter Thread starter ck26
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ck26

I just noticed that my USB powered media card reader light was on even
though the machine was off. Is this right? I would have thought that the
machine couldn't power the device even in standby mode if the computer was
switched off. I only noticed this today when I switched the machine on and I
got a STOP message and when I disconnected the device and put it into a
different port and rebooted, I got no problems until the next time I
rebooted and the same thing happened again.
 
Some motherboards implement a "Soft Off" option, where power is not totally
shut down. It is vendor specific and usually controlled by a BIOS option.

Marc Reinig
System Solutions
 
Some motherboards implement a "Soft Off" option, where power is not totally
shut down. It is vendor specific and usually controlled by a BIOS option.
Click to expand...


It is not controlled by the BIOS.

The BIOS only offers the possiblity to power-up by an already powered,
active USB device. For these USB devices to be already-active, there
MUST be a hardwired 5VSB circuit to the USB ports. That is solely a
motherboard circuit design decision. Some boards (particluarly old
ones) do not have 5VSB for USB ports, while newer boards do, and often
have a jumper to choose whether it's the 5VSB or main 5V rail powering
these USB ports.


Dave
 
As I said, it is vendor specific. It may not be controlled by the BIOS on
yours, but on mine, it is. It is a motherboard circuit design controlled by
the BIOS: Enable Soft Off / Disable Soft Off.

Marco
 
As I said, it is vendor specific. It may not be controlled by the BIOS on
yours, but on mine, it is. It is a motherboard circuit design controlled by
the BIOS: Enable Soft Off / Disable Soft Off.

Marco
Click to expand...

No, it is not vendor-specific. Your "enable soft off" setting is only
deciding if the system turns on, not whether the power is on. This
thread is about USB ports being powered when the system is soft-off.

ONLY the ability to turn on the system is controlled by the BIOS. The
power supply going to the port is not controlled by the BIOS.

If you know of a PC system that uses BIOS + logic to switch power
supply rails, please provide a verifiable example.



Dave
 
Anyway thanks guys, I take it that this means there's no problem that
there's power going through the device when the computer is not on?
 
Anyway thanks guys, I take it that this means there's no problem that
there's power going through the device when the computer is not on?
Click to expand...

Correct, though if you didn't want the port powered there might be a
jumper to change that, check the manual.


Dave
 
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