Power Supplies to USB Sockets

  Blott 11:57 22 Aug 2007

Sorry to appear a bit thick, but can someone please educate me in how power is supplied to USB sockets.

I have USB docking/charger for a PDA.

When I power off the computer by normal means, the computer shuts down, but power remains on the USB docking device ( little light on the front remains on). But, if I then turn off the power switch on the back of the computer for a few seconds the light on the device goes out, and remains out when I put the switch back on.
Then remains out until the computer is powered on again.

My question really is, is it OK to leave the device on and charging the PDA when the computer is turned off ? If the USB socket is still being supplied from the mains I take it this will be OK, but I fear that with the computer off I might be running down a battery or damaging come component inside the machine.

Sorry about this - pretty basic I know - too basic for the books I've looked up to cover.

Best regards to all


  Chris the Ancient 12:31 22 Aug 2007

When you power down your computer, the power supply stays 'live' so that it can detect the on/off switch being operated. The power supply staying live all the time has the side effect (sometimes) of keyboard lights and usb ports staying on. This is perfectly normal.

I can see no problems with leaving your PDA charging up through the usb while the computer is off.



  Totally-braindead 15:26 22 Aug 2007

It depends on whether the PDA will stop the charging when it is fully done. If not and it keeps charging it might effect the life of the battery as it would be effectively overcharging the battery. But considering the low current provided I think this unlikely to cause a problem, unless its left on for days and weeks at a time.
Personally I would disconnect it when not in use.

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