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Alan Winstanley Friday, December 01, 2017 by Alan Winstanley

Triggering USB into operation

Am I right in thinking that a USB port has to be kick-started into action with an initial high(er) load before it operates?   My Logitech illuminated keyboard won't work again once my PC hibernates, I have to unplug and reconnect it.  I suspected that the USB port fails to trigger into operation again when the PC resumes.

The number of times I've started typing blindly only to find the keyboard isn't connected...  Others have suggested a powered USB hub might do the trick.



  • by  PeterTraneus Anderson
    Was your keyboard illuminated when you "started typing blindly only to find the keyboard isn't connected"? If so, the problem isn't USB power, but rather your PC not re-scanning (or whatever the correct term is) for USB devices upon coming out of hibernation.
  • by  Alan Winstanley
    @ Peter,  that's a good question -- I'll find the answer next time it stops working and report back.
  • by  Alan Winstanley
    It just happened again - the (illuminated Logitech) USB keyboard isn't illuminated when the PC wakes up, I have to unconnect and reconnect it.  For bus powered USB peripherals I thought the port needed to deliver up to 100mA before it finished configuring. Maybe it's a power supply issue.
  • by  PeterTraneus Anderson

    So the USB power to your keyboard is not coming back on when your PC comes out of hibernation. How do you trigger your PC to come out of hibernation? A USB mouse, perhaps?

    For bus-powered USB, the host port on the PC can deliver up to 500 mA at 5 V, and each port on a hub can deliver up to 100 mA.

  • by  Ian Stedman

    Goto device manager, select the USB keyboard, right click and select properties. From the properties menu, look for the 'Power Management' tab. The 'Allow this device to wake computer' should be ticked. Also check the 'Allow computer to turn off this device to save power' option is unticked or as on my PC greyed out.

    I'm assuming you use Windows.


  • by  Alan Winstanley
    Ian,   thanks, I've looked at that (Windows 7)  and Allow device etc is ticked and Allow computer etc is  in fact greyed out like yours.  Elsewhere I'm reading how some users of Logitech illuminated keyboards are having the same problem,  one suggestion is to try through a powered hub, or untick Allow device to wake computer instead, which I'll do next.

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