You may have heard of the MintyBoost, a DIY kit that lets you charge USB devices using AA batteries. Well I have a problem, and I was hoping you guys might have a solution.
The kit is fairly simple, it just uses a DC-DC converter to convert the 3v to 5v that you need to charge USB devices. But unfortunately, my Motorola Atrix MB860 phone is stupid. It tries to draw as much current as possible, whether or not the charger identifies itself as a "Fast charger" according to the USB standard. It can draw up to 1A, and typically draws 850mA, to charge its large 1900mAh battery as fast as possible. So my charger works fine, at first, until the IC gets so hot that it shuts off, and then it cools down, turns back on again, this happens at first every 10 seconds, then every 5, then every 1s, then so fast that the CPU usage on the phone goes to 100%. The PCB of the charger got so hot that it melted the foam sticky pad that was used to mount it in the tin. The 2450mAh NiMH AAs got so hot that if I held my thumb on them for more than 3 seconds, it hurt.
Is there any way to rescue this circuit to prevent the phone from letting it draw more than 500mA? Some kind of current limiting resistor in there or something?
The kit is fairly simple, it just uses a DC-DC converter to convert the 3v to 5v that you need to charge USB devices. But unfortunately, my Motorola Atrix MB860 phone is stupid. It tries to draw as much current as possible, whether or not the charger identifies itself as a "Fast charger" according to the USB standard. It can draw up to 1A, and typically draws 850mA, to charge its large 1900mAh battery as fast as possible. So my charger works fine, at first, until the IC gets so hot that it shuts off, and then it cools down, turns back on again, this happens at first every 10 seconds, then every 5, then every 1s, then so fast that the CPU usage on the phone goes to 100%. The PCB of the charger got so hot that it melted the foam sticky pad that was used to mount it in the tin. The 2450mAh NiMH AAs got so hot that if I held my thumb on them for more than 3 seconds, it hurt.
Is there any way to rescue this circuit to prevent the phone from letting it draw more than 500mA? Some kind of current limiting resistor in there or something?