Keep USB power ON while laptop Sleep's

Hello

Why, and how can I prevent it, does the power to USB devices go off when the PC is in power saving mode (ie goes to Sleep ) - even though all the usb controllers are set to not allow the pc to turn off the usb, (box unchecked) and the usb selective suspend mode in advanced power settings is set to disabled. BIOS set "Enable wake on USB" as well.

(This is to charge an smart phone overnight, but without everything on).
(I have seen other posts where the problem is the reverse: namely they can't switch it off. But my problem is that I want USB power to be on.)

Windows 7 Ultimate, DELL Latitude D630, BIOS A17

I hope it's something simple and obvious.

Thanks in advance...