On Fri, Jun 17, 2011 at 8:44 PM, V G wrote: > Hey all, > > I'm trying to charge (let's say) a single Li ion battery (float charge) t= o > 4.0V. > > The maximum charge current will be controlled with a BJT (tell me if > there's a better way) and so I've been doing some simulations to see if I > can actually get 4.0V across the battery this way. > > Screenshot of simulation: http://solarwind.byethost7.com/pic4.png > > I'm pretending that R2 is the battery, gradually increasing its impedance > as it's state of charge increases. The voltage across the battery never > seems to hit 4.0V. I'm doing another simulation with R2 from 1-100k and t= hat > seems to get closer and closer to 4.0V as the current goes to 0 and the > BJT's impedance rises rapidly. > > I can understand that at the beginning, the BJT needs to decrease impedan= ce > as R2 increases in order to maintain the overall impedance so that the se= t > amount of current goes through. I don't understand though, why just befor= e > 40 ohms on the x axis, the BJT impedance increases again. Shouldn't the B= JT > try and lower its impedance as much as possible so that the most current = can > go through (even though the maximum amount allowed by the base current ca= n > no longer go through)? > > What is this minimum impedance and why is it there? > Nobody? --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .