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Configuring USB voltage output

Asked by Joseph Lapp

I want to change the voltage output of one of my USB ports to less than the 5.0V it puts out standard. I know this is possible with windows, so there is no hardware limitation, but the only dev file I can find relating to USB power sets it's current output. Any help would be appreciated.

The reason for this is that I have several USB powered devices that use lithium ion batteries which I don't want to risk over-charging.

Thanks for your help.

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David Mawdsley (dm-madmod) said : 		#1

I'd strongly recommend that you NOT try to change output voltages from your system board to a USB port using a "fix" in a configuration file. Changes, even if you can successfully change them, can have unintended consequences that could damage your computer or equipment outside of it.

Instead, I suggest that you use a dropping resistor circuit outside the computer from the USB port that supplies 5 VDC. Start with a visit to the site: http://en.wikipedia.org/wiki/Voltage_drop to get an overview of what you need to consider.

If, for example, you needed to drop 5 VDC to 4 VDC, you need to figure a resistor value for a resistor in series with the circuit to drop the voltage as desired. Whatever your circuit turns out to be, do the math multiple times and check your wiring before powering on.

Best of luck Joseph.

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Joseph Lapp (joseph-lapp) said : 		#2

Thanks David, I'm actually an electrician me and ohm's law are good buddies. I was hoping to find a software solution to this before fabricating a circuit. I do believe that a software solution to this problem is possible, although I'm starting to think that Linux doesn't have a dev file to adjust voltage outputs.

Revision history for this message
Joseph Lapp (joseph-lapp) said : 		#3

Thanks David, I'm actually an electrician me and ohm's law are good buddies. I was hoping to find a software solution to this before fabricating a circuit. I do believe that a software solution to this problem is possible, although I'm starting to think that Linux doesn't have a dev file to adjust voltage outputs.