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Using VSB 5v Power To Keep USB Device Alive When Computer Is Off ?

Hi,

I have a USB device which I want to keep powered when the computer is turned off (not standby or hibernate but off) - but still plugged into the mains. i.e. the PSU is still 'live' but the fans are not running and I beleive only standby power (VSB) at 5V is supplied to the purple wire on the ATX power connector to the motherboard.

Can I wire the red and black wires from a USB cable directly into the power connector (to purple 5v VSB and black wire ground) and expected my USB device to receive 5v power to keep it running ?

Is it dependant on the powerdraw of the device ?

I haven't put a meter on the ATX purple wire yet but would appreciate some feed back if what I'm thinking of is feasable.

Thanks.
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rcscs
Asked:
rcscs
1 Solution
 
CallandorCommented:
According to the ATX specification http://www.formfactors.org/developer%5Cspecs%5CATX12V_1_3dg.pdf, VSB is supposed to stay on when all the other rails are off, and should be capable of providing up to 2a @ +5V +/-5%.
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rcscsAuthor Commented:
Thanks Callandor.

Successfully tried this today.

Wired a the red and black cables from a 'chopped' usb cable directly into the ATX motherboard connector (purple and black connections) and found that I could successfully charge/power my USB device even though the computer was 'off'.
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