 Max 1797
with a Potentiometer Dimmer Circuit

This design eliminates the need to etch a circuit board for the small surface mount chip.  Peripheral components are large "through hole" items soldered together on a blank board.

Results for Max 1674 are similar.

 i, amps (two white leds in parallel) dV, volts, across  R=.333 ohms dV led, volts 0 0 2.40 .010 .0033 3.09 .020 .0066 3.25 .050 .0167 3.55 i, amps (1 watt  Luxeon Star) dV across  R=.333 ohms Vled 0 0 2.40 .100 .033 2.87 .200 .066 2.99 .275 .092 3.08 .300 .100 3.10 .325 .108 3.12 .350 .117 3.14

note:  R is three 1 ohm resistors in parallel.
1/R = (1/1) + (1/1) + (1/1) = 3, so R = .333 ohms

 Output Voltage IC Operating Temperature, Degrees C Degrees F 2.58 38 100 2.94 46 114 3.11 54 129

From Max1797 and Max 1674 data sheet:
Ambient temperature range is -40 C to 85 C, with a maximum junction temperature of 150 C

Efficiency:

dVin = .185 volts = I R
I = dV/R = .185/.333 = .555 amps
V bat (2C nimh) under load = 2.34 volts after going through R = .333 ohms
Vout to led under load = 3.15 volts, I led = .365 amps (extrapolated from data above)
P = V I
Pout/Pin = (3.15)(.365)/(2.34)(.555) = .885