USB power in parallel
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I have a few external drives that have a dual usb end for tapping more power
for the drive by using 2 ports. In most cases, these drives won't work with
just one port. Looking at drive specs on portable, port-powered drives like the
Western Digital ones, they can take 1000mA to spin up, and many take 700mA.
With port power restricted to 500mA, it makes sense why I can hear it can't
spin up with just one usb connection.
I'm assuming the second connection to the pc is power only. How can they just
parallel ports? Is that part of the spec, or just a hack (like making a simple
and gate by paralleling OC outputs)?
Has anyone built an add-on pack that would just power during spin-up by
paralleling batteries and perhaps a regulator? Not all the time, so the port
can power the rest of the time and save the batteries. Could it be sensed by
voltage drop? Do any simple, passive circuits come to mind?
In reply to: <7AC59A75-5D02-4835-8023-FC4A7F0DE79E@nope9.com>
See also: www.piclist.com/techref/power.htm?key=power
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