[sdiy] usb power?

[Ullrich Peter]

Normally every USB 1.1 and 2.0 port should be able to deliver 100mA - even Port on an USB Hub.
Especially ports on the root hub and ports on active hubs can normally deliver 500mA.
Under USB a device should normally tell the PC that a higher current is needed (and also tells the value)
but only a few PCs take really care of it as the special USB power controllers that can control and check the 
USB power cost some money...

Most motherboards simply have silicon fuses (from Littelfuse, bellfuse)
that make a self healing fuse in case of a shortcut to GND. You can see them as little green rectangles on 
your motherboard (normally 1X1 is written on them).

So in most cases you can source 500mA out of a (active) USB port even if no device is "enumerated".

Ciao
Peter


http://www.ullrich.at.tt

________________________________________
Von: synth-diy-bounces at dropmix.xs4all.nl [synth-diy-bounces at dropmix.xs4all.nl] im Auftrag von db [dbarton at pacbell.net]
Gesendet: Sonntag, 22. März 2009 08:59
An: synth-diy at dropmix.xs4all.nl
Betreff: [sdiy] usb power?

I want to power some lights from my laptop. These lights are a bank of 25
leds, designed to run at 4.5 volts

How can I tell how many of these are ok to power from usb?

I'm guessing a usb hard drive pulls more current than even 100 LEDs, no?

dennis.barton:skylab2000[socal]



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