On Mon, Sep 5, 2011 at 7:27 AM, V G wrote: > 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 t= he > 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 giv= e > 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 do= ne > 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, fo= r > opamp voltage output stability. Note that there's also C2 (beside the > MOSFET) as well, which I believe serves the same purpose. > Anyone? :( --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .