On Fri, 03 Dec 2004 00:56:40 -0800, Winston
wrote:

(Snip progress report)

Excellent! Thanks, Don.
Are you driving these guys with some kind of current-regulated supply?

Just a resistor so far. I'll probably use LM317's as current
regulators for the microscope lights because it's easy, simple,
cheap, and neither size nor power efficiency is important there.

Do you envison a switchmode driver in your rechargable light or
are you going to stay with a series resistor?

I designed a little SEPIC regulator and had a few printed wiring
boards made, piggybacked on another project. They're about 1"
dia, fit nicely behind a Luxeon Star. SEPIC is good if 3 or 4 cells
are used because it can operate with supply voltage either higher or
lower than load voltage. For 2-cell operation (boost only) I can
omit a few parts and it then degenerates to the Zetex appnote circuit.

Ian Sterling's approach of using a micro is the way to "do it right".
That should provide much better regulation than the so-called "LED
driver" chips do and it offers other features like different
brightness levels, etc.