On Fri, Jun 17, 2011 at 3:07 PM, V G wrote: > On Fri, Jun 17, 2011 at 3:05 PM, V G wrote: > >> On Fri, Jun 17, 2011 at 1:44 PM, RussellMc wrote: >> >>> > How large have you made the R1/R1 combination and still gotten decent >>> > voltage tolerance over "room" temperature range? >>> > >>> > The input bias current is rated at 2 to 4 uA +- 0.8 to 2.5 uA over >>> > temperature range 0 - 70. >>> > >>> > Lots better than a zener but maybe would drain the battery fairly >>> > quickly unless the R1/R2 pair was very high and then input bias curre= nt >>> > shift eats away at accuracy. >>> >>> His app is a charger. >>> Power will be on most of the time and even if off is not going to >>> cause vast problems over charger residency type periods. >>> >>> 18650 LiIon are about 2000 mAh + . >>> >>> 1 mA drain at 24 hours =3D a bit over 1% capacity. >>> 100 UA - ~0.1% >>> 10 uA ... >>> >>> In order to avoid thinking about temperature compensation I suggested >>> he move the voltage back another 0.1 V to 4V. >>> This reduces capacity but (probably) allows simple float and greatly >>> improves cycle life. >>> Also avoids having to do current tail level triggered charge terminatio= n. >>> >>> >> >> Okay so I figured out another mechanism to charge. Uses a few transistor= s, >> but simplifies the charging itself. >> >> I'm guessing many will find this design messy and unnecessary. Please >> comment. >> >> Here's my circuit: http://solarwind.byethost7.com/pic2.png >> >> The left side MOSFETs, when enabled, connect the batteries in series, >> allowing regular discharge. >> >> The right side MOSFETs and BJTs, when enabled, do a parallel current >> limited charge up to 4V. As far as I know, the BJTs won't allow the >> batteries to charge each other when the BJTs are disabled. When they are >> enabled, the batteries are charging anyway. My only concern with this de= sign >> is reverse biasing the BJTs and the batteries charging each other when i= n >> parallel charge mode. >> >> I plan to use SOT-23 transistors to keep it small. Battery discharge I'm >> guessing will be maximum 1A (to charge my iPhone). Battery charge will b= e >> around 2A per cell. >> > > Whoops, just noticed that my NPNs should be low side. Will fix now. > Updated and much more simplified circuit. http://solarwind.byethost7.com/pic3.png I don't know if the series MOSFETs on the left are correctly oriented and i= f they'll safely let current flow when enabled. Are they even biased correctly? --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .