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There are some circumstances where I would like to switch off power to a USB port, but still allow the port to function as normal.

Is it possible to switch off power to a USB port using software settings?

and...

If power to a USB port is turned off, will it still function as normal (ignore devices and functions that require the power usually supplied through a USB port, e.g. external hard drives, charging of phones)?

[edit] Nobody seemed to read the "circumstances" link I had in the original post. So here it is as it relates to this question:
If your notebook is low on power, and you require a connection to your phone (e.g. for tethering to the internet), the connection with the lowest possible power use that I can think of is a USB connection, but only if the phone does not draw power to charge itself.

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Could you clarify abit, why this could be useless? Most devices you input into a USB port is requiring power to operate, the only thing I could think of would be phones tha already had power og an external harddrives with and external power supply. –  Patrick Jørgensen Apr 24 '12 at 8:20
    
Its possible to switch off power, I know this because Zentimo xStorage Manager software can do this after removing a usb device using their software, just don't know how they do it. Would be a nice experiment to see if the communications bus remains active after you somehow disable power. –  Moab Apr 24 '12 at 11:14
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1 Answer

up vote 3 down vote accepted

The simple answer is no, if you remove power to that USB port it will not function as a USB port.

Part of the specification is for power, and all devices plugged into a USB port expect power.

What is it you are trying to achieve? That may help us provide an alternative answer you can use without trying to breach the spec.

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I've updated my question with a use-case. Since the spec includes power, I'll approach the problem from the other side. It'll be interesting to see if there are ways to prevent a phone from charging when plugged in to a USB port. –  chobok Apr 26 '12 at 10:05
    
@chobok - The phones on the market today do not provide a method to not charge unless they are already fully charged. Its an engineering decision, 99.9% of people want to charge their device, when they plug in the cord. –  Ramhound Apr 26 '12 at 12:38
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