fyi high current drivers cheap on ebay
I just picked up 10 of these for playing with. I wanted to attach a 2 D cell light to my bicycle, and run it off the 12v battery in the pack. The light is probably just using the cell resistance to limit current, so 12v source would be bad. I didn't want to use a linear regulator since there was going to be a very large voltage drop required (12v down to about 2.7v) that would not only heat up the regulator but also severely shorten my battery life.
I found these "buck-down" regulators on ebay. There are several variations on them, some that are voltage regulators, some that are current, some that do both. This one just does current, which is really what you need to power a higher output LED like those in the 1-3 watt range.
http://www.ebay.com/itm/251066005460
He's selling them for a buck sixty (+free ship) which is hard to beat for what it does. I've installed the regulator in where the D batteries were and it's working really well. Buck-down regulation is a very efficient way to limit current to LEDs, so the regulator doesn't get past skin temp warm when passing an amp at 2.7 volts. There's a multiturn pot on the board to dial up the current. It's well-regulated as long as the output resistance doesn't change, which shouldn't be an issue for driving an LED. The only problem I've ran into is there's a good deal of switching noise. This regulator ships with a 220uF on the input and output, but nothing smaller. There are pads on both ends however where a SMC could go, I will try adding 0.01uF on both ends and see if that keeps the noise out of the 2m radio that's also on the bike. (running on the same 12v battery, but the noise is NOT coming in through the DC, it's radiating and picking up on the antenna)