> > >I am just looking for some feedback on a circuit design idea I am > > >playing with. > > > > > >I am thinking about building a gel cell charger using the UC3906 > > >charger IC. While the design is straight forward, it requires about > > >16V input voltage to charge a 12V gel cell with dual step mode. > > > > > >I hope to use this charger in a motorvehicle or camper. So my power > > >source is a lot closer to 12V then 16V. I did this for a commercial product many years ago. I don't believe that the economics would have changed too much. Work out your worst case input requirement for the charger itself - which you have already done by the look of it. Select an input voltage that is the greater of the minimum your charger circuit requires or the maximum input voltage. Now build a step-up converter that will take the minimum input voltage* and provide the voltage needed for the charger circuit. Doing it that way avoids the complications that arise when the two voltage ranges overlap. So even if your battery needs 13.6V and the car supply is at 14.8V, it still gets stepped up and back down again. That may seem less efficient, but power efficiency isn't the only criteria. * The minimum input voltage needs to be either the minimum that the circuit will see or the value that some form of protection circuit will enforce. ie. In a car, you don't want your circuit to work at 6V for anything longer than a few seconds. If the supply is that low, then you have more important things to do with your electrons than charge an accessory battery. Steve. ========================================== Steve Baldwin Electronic Product Design TLA Microsystems Ltd Microcontroller Specialists PO Box 15-680, New Lynn http://www.tla.co.nz Auckland, New Zealand ph +64 9 820-2221 email: steve@tla.co.nz fax +64 9 820-1929 ========================================= -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body