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powered USB ports?

Posted on 2001-06-25
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Last Modified: 2013-11-09
are all usb ports that come pre-installed on desktops and laptops powered? I'm talking about the ones that are either part of the motherboard or PCI.
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Question by:dolfanMT
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by:magarity
ID: 6225594
Usually, but not always.  Check the manual for the motherboard or laptop in question.
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rayt333 earned 50 total points
ID: 6226107
Like magarity stated usally they are powered but most only have a small amount to power an external device, if you are installing a device that requires a high load then you would be better off with a externally powered USB hub.

You will need to check the power requirements for the device and also see how much is available from the USB port.
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by:jhance
ID: 6226179
See:

http://www.allegromicro.com/techpub2/usb/power.htm

USB ports should provide up to 500mA of current at 4.5 volts.  Some laptops, however, do not provide any power at all since they don't really have much to spare.  Strictly speaking they are not USB spec compliant but that's life...

In general the specification for your laptop should define how much power, if any, is available to be drawn from the USB port.
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Expert Comment

by:zouying
ID: 6231029
USB ports should provide up to 500mA of current at 4.5 volts

Actually, each of the ports is allocated 100ma. Besides the hub controller requires 100ma, you have 400ma left, which means, one hub has up to 4 ports, if bus-powered.

Well, in the drivers codes, all of these ports are powered up, actually, the port status is 0x0000100.

Maybe too much info to you.

Z/
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by:ComTech
ID: 6373352
Hello everyone,

This question has been open for quite awhile. I am going to allow feedback from the questioner and experts. If it is not resolved, I will delete or accept an answer based on the info I have been given. Experts, feel free to offer input. I will monitor this question for a period of 5-7 days and come back and evaluate.  

I reserve the right to disallow any comments that may not have a direct conclusion

Thank you,
ComTech
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*Question Author, please return and resolve this question.
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Expert Comment

by:ComTech
ID: 6393929
According to PC ISO, all onboard USB ports are powered, albeit usually by not much.  rayt333 has the correct answer.

Thanks,
ComTech
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