> Another issue is that LED forward voltages have been climbing and 
> the
> LM3909 won't handle white, blue or some green LEDs. It's obsolete 
> for good
> reason.

The 2 transistor circuit that I posted yesterday will handle any 
available single LED forward voltage due to it's inductive flyback 
action. I note that eg Luxeon are mounting multiple LED's per "LED" 
and are in some cases placing them in series. It may handle these too, 
although when you get to higher power levels the cost rises and a more 
modern 1 cell LED driver is probably a reasonable choice.

Any processor that will run on the desired voltage plus one transistor 
and an inductor will meet the requirement.

If manual startup is acceptable such an arrangement can self power the 
processor from the flyback voltage and allow eg a 3v processor to 
operate on eg 0.8v supply. Total parts count could be as low as LED, 
processor, 1 x transistor, 1 x R, 1 x D, 2 x C, Inductor, battery.



            RM 

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