the “NANJG 28” apparently has a linear regulator for power sources with a higher Voltage than the LED’s vF, as well as a boost circuit that works pretty well.
I’m picking up one for the empty 2xAA Solarforce L2R body I ordered. I may just bypass the PIC entirely to make it 1-mode.
Sic22 posted some good but slightly hard to read numbers here:
His numbers indicate that the voltage/current/regulation/whatever falls off very quickly when input-voltage drops below 2.3v. It’s not so severe that the product becomes unusable, but it’s significant. So this driver may not be -ideal- for use with crappier Alkaline or NiMH/NiCad batteries, but with higher quality cells such as Eneloop NiMH or Energizer Lithium Ultimate… looks like it ought to do 1.8hr+ or 3.7hr+ respectively before falling below 2.3v total for a pair of cells. For some reason Energizer Advanced Lithium looks really pitiful in comparison though…. Seems to me like it would provide well under an hour. The data sheet is almost blank, but what is there is totally not encouraging (the Constant Current Performance graph).
For kicks, here’s the Alkaline data sheets for normal and e2 (now obsolete and replaced with lithium):
it -looks- like they could probably provide around 20-30 minutes above 2.3v.
so good deal… 2hr of light on eneloops, probably 4hr of light on Lithium Ultimate.