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Subject: USB based charger

USB based charger

From: Andrew Jamieson <>
Date: Sat, 18 Jan 2003 15:10:20 +1100

I've constructed a quick and dirty USB based charger to see if the idea had
legs, and I'm happy to say it works :) !!!! As this was a proof of concept
proto, I cut a switch-mode regulator from an old PCB I had lying around
rather than building one from scratch. However, now I know its worthwhile,
I'll design a proper circuit for it.

I've constructed it as a small box with USB A plug and power jutting
directly out of one side, and USB B in on the other. So its basically just
a small dongle box (160 X 35 X 35 mm) that plugs directly into the bottom of
my AJB. A switch on one side controls the routing of the USB bus power
signal to the AJB, so that even tho the USB plug is in at all times you can
switch USB mode on and off. A standard USB cable (A-B) plugs in the back of
the dongle, so there's no need to carry your cable around all the time.

Voltage output is set at 8.6V, which draws about 450mA from 5V with BL on
and HDD spinning up. I may bump this voltage up a bit, as I am not 100%
sure the net current input to the batteries is positive when playing music.
It may come to a close trade off between charging when playing and
overloading the USB port tho ....

I need to test the USB transfers at high speed (although I dont have a
recorder, I do have access to various USB2.0 based mass storage solutions),
and investigate if this will work charging a recorder (ie will not overload
the USB port). I will keep you posted.

Received on 2003-01-18

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