Thanks for answering guys!
I read through those links and not sure if I understand them fully or can use them. Some requirement bullet points:
- The current source circuit has to be "on top" of the load, so hooked directly to the supply. Page 7 of the
DS2714 datasheet should show why.
- With a 5v supply, the highest battery (being charged) voltage of 1.65v, and the Vce_sat of the switching transistors (again on page 7 of the link, but not using those exact PNPs) of ~0.1v, I have a minimum voltage differential of 3.25v to work with. When a weak cell (~1.2v) is inserted, the differential goes up to 3.7v.
Another issue: From the little I know about SM regulators, parts placement is VERY important to avoid induced voltages in the wrong places. If I use any of these projects, I would be etching my own PCB, which I have done exactly once about 15 years ago using RadioShack stuff (masks and pen to make the traces).
As I was doing some more searching, I came across
this (scroll to the end). I happen to have a few completed PCBs using a version of the main IC, but set up to be a
voltage regulator. Adding the additional sense resistor, two Opamps, and the other support components to the feeback loop would be fairly easy (I think).
I was hoping to use an LM317T somehow and just add the coil, diode, and a few other support components. I guess this is what I get for jumping into something a little more than I can handle.