5vdc from a USB 3 port

Colin's picture

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Joined: Nov 13, 2020

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5vdc from a USB 3 port
November 13, 2020 - 1:36pm

We are trying to use a spare USB3 port on a PC to drive an LED as an indication that the PC is powered ON. The PC has a power on LED but it's in a rack and is not visible to the operator. We have connected the LED across the USB3 VBUS and USB 3 GND pins and have discovered that it doesn't work. We believe however that it would work with a USB2 port (as I have found numerous articles telling me how to get 5VDC from a USB 2 port by simply connecting the red and black wires to whatever we wanted to power). Can anyone please confirm that USB3 operates differently ? Our tests would suggest that the power isn't available unless the PC detects the presence of a device connected across the data pins. If this is the case can someone please advise if there is a simple way to trick it to believe that there is a something there ?

Michal Podmanický's picture

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Joined: Nov 06, 2020

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Why not to use a better source of information about runnig PC, like power ON Led.

 

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Colin's picture

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Thanks for your response. The computer is a sealed mission computer so we have no way to access the internals and only can make use of the pins that are available on the interface connectors. The USB 3 port is the only thing we can potentially make use of.

Michal Podmanický's picture

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Joined: Nov 06, 2020

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And advice:

Discover if your PC_Led- pin is Gnd, I draw this schematic as an example only.

If you can be safe to not damage your PC, use an optocoupler to sense PC_Led voltage.

Colin's picture

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Thanks for your response. The computer is a sealed mission computer so we have no way to access the internals and only can make use of the pins that are available on the interface connectors. The USB 3 port is the only thing we can potentially make use of.

Sourav Gupta's picture

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Joined: Feb 12, 2018

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PC USB3 port generelly provide power without any additional detection. However, what is the connector type? Connectors have different protocols such as type C.