I have a A123 battery (2300mAH) I want to charge in a reasonable time (3-4 hrs).
I have the battery, charger & a circuit board in a small box. I've tried the LM317 CC/CV circuit for charging but the problem I've found is the heat dissipation inside the box & it's possible long term effect on the circuit board. The external PS can be either 9V or 12V - so there is probably too much heat dissipation in reducing the voltage. I can't reduce this external PS.
I've decide to use a buck converter based board on the MCP2307 - these can be picked up cheaply & with a bit of modification can be adjusted from an output voltage of 3.3V to 3.6V (the max voltage for LiFePO4 charging). These boards are not reducing current however so I need to implement a high voltage sensor cut-off. The MCP2307 has an enable pin that when high turns on the regulator.
So I wanted to implement a simple comparator based voltage sensor that would turn off the MCP2307 when the battery reached 3.6V. I also wanted one that signaled if the battery fell below 3.0V. I have LM393 comparators in stock
So I guess I need a voltage reference like a TL431? Has anybody got a simple circuit using these parts?
My other slight concern is that the MCP2307 outputs about 2A current while charging so if I turn it off when the battery reaches 3.6V what percentage full is the battery?
Edit: Actually, this may not be of concern as these batteries are meant to be able to be charged fully in 15mins or so at high C