Circuit (click to enlarge) [image: cc.png] http://solarwind.byethost7.com/cc.png I designed this Li-ion charging circuit so I could select my own maximum charge voltage (so I could get a better service life out of the cell by charging it up to only 4.0V or less). At the same time, I can fine tune the maximum charge current. This method (constant voltage with current limit) models (as far as I know) the normal method for charging Li-ion (constant current until a certain voltage is reached, then switch to a constant voltage). I would like some suggestions for it as I'm pretty sure there are a few things to improve. * The chip in the middle is a high side current sense amplifier. * The voltage source on the left is my best attempt at modelling a Li-ion battery. It gains voltage as it's being "charged" (DC operating point stepped to increase voltage). * Graph: ** cyan: power dissipated by the MOSFET ** blue: current through r_sense and the battery ** red: MOSFET gate voltage ** green: voltage across the "battery" Questions: * I placed C2 (next to the MOSFET) to smooth out the gate voltage and give = a more "analog" signal so the MOSFET can control the current better. Thoughts about this? * I chose a MOSFET instead of a BJT so I can get the full 4.0V out of the charging voltage source. Thoughts? * What are your general opinions about this circuit? Could anything be done better? Is the whole concept here stupid to begin with? * Is C1 (above the opamp) too large a value? I was suggested a value of around 50pF a while ago while designing using a similar circuit block, for opamp voltage output stability. Note that there's also C2 (beside the MOSFET) as well, which I believe serves the same purpose. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .