How can I switch off power to a USB port (without disabling the port)?

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.

chobok

Posted 2012-04-24T08:11:14.443

Reputation: 224

you may use wifi/bluetooth tethering for that while. I'm not sure if cutting out the outer power pins of usb would leave your phone detected to pc. – d-coder – 2014-10-05T15:01:45.917

Another use case: I wrote an app to switch off WiFi on my phone when the screen goes off, unless the phone is charging or in a VoIP call. Now it works, but it was hard to debug over WiFi or USB if both are off/disconnected! Emulation was not an option as this is to replace a missing feature in Android 8.1 and emulation of newer Android versions is not supported by Google on AMD/Ryzen processors yet. – nsandersen – 2019-04-11T09:15:05.853

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 – 2012-04-24T08:20:26.757

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 – 2012-04-24T11:14:55.913

Answers

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.

Rory Alsop

Posted 2012-04-24T08:11:14.443

Reputation: 3 168

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 – 2012-04-26T10:05:33.487

@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 – 2012-04-26T12:38:29.057

I've just tested this by cutting the red wire of an USB-Cable. If the other device is powered, it still works fine.

der_do

Posted 2012-04-24T08:11:14.443

Reputation: 21