Need to hack a driver for extreme modes.

I'm building a larger headlamp for caving and having trouble figuring out a good driver to use. I need a fairly wide range of currents for my purposes. I want a high setting that can light up the world for large passages and deep pits, but would only be used for <1min at a time. I want a medium setting for moving around the cave, and I want a really low setting for tight passages and any time I'm stopped. First let me spec the build so you know more what I am looking for. I am leaving some flexibility in my design to allow for different driver possibilities.

Going to power it using 18650's in 1S2P, 2S1P, or 3S1P configuration depending on what voltage I need.

Looking at powering 2, 3, or 4 neutral white XM-L's in series (prefer 4, but could do as few as 2 if constrained by driver options).

Want 3 modes across a huge range (~3000mA, ~700ma, ~100ma) oo:

Probably use a magnetic switch.

The smaller the better, but anything ~1"^2 should fit in my housing.

Don't think PWM would be a good option in this case for a number of reasons.

And of course better efficiency is always appreciated.

I'm willing to drop some decent money (~$30) on a good driver or do the work to hack/build one that suites my needs. I'm not good at electrical design, but I'm good with a digital soldering iron, so if someone could help me design something, I should be able to build it (or be willing to pay for one you build for me). I have seen some hacked Deal Extreme designs posted, so thinking something along those lines might be the way to go. Don't care if it's boost or buck, but efficiency (and lack of heat production) would be great. Could 2 drivers hooked together do what I'm asking? Any ideas would be greatly appreciated.

Thanks, Eli

Taskled may have exactly what you are looking for, maybe without any modifications. Just watch out for heat issues with them leds. They do get mighty hot when driven at or near the 3A mark.

OK, so found the magical link:
http://www.videofoundry.co.nz/ianman/laboratory/research/driverlist.php

After looking through all the options, I think I'm going with this one:
http://www.lck-led.com/p501/Constan...oduct_info.html?osCsid=e185bed66d8248ba0733dd

Pretty close to the mode ranges I was looking for and it will allow me to run 3 XM-L's off a 3S1P or 2 XM-L's off a 2S1P 18650 setup. It sounds like the manufacturer is fudging their numbers a little, but it should meet my needs sufficiently.

Thermal management will be well taken care of in my design, but I don't think it will be too much of an issue regardless, because I usually use my light in medium (20% of the time), low (75% of the time) or turn it off (5% of the time). High is just for looking around large rooms, up into domes, down pits, and figuring out where you are going.

Guess I figured this one out on my own, but hopefully someone else will run across the same issue and find this post helpful.

Peace, Eli