I'm playing with power LED's again, and I've also gotten a handful of infrared laser diodes in the 200-500mW range.
LED's require a constant CURRENT source rather than a VOLTAGE source, as I understand.. and laser diodes are just special-case LED's.
Until now, I've been using LM317's wired as a current regulator :
But I've seen a number of different methods, including transistors and zener diodes, as well as op-amps and switching regulators: (Images: Wikipedia)
I use the LM317 circuit because they are cheap, but they do require a pretty high wattage resistor, and the whole circuit wastes a lot of power as heat. Usually I attach a heat sink otherwise it gets pretty dang toasty. The photo above shows a 10 watt LED with a hack-job LM317 regulator screwed right into the heatsink, scavenged from an old PC CPU. Works well, but it gets awfully hot. I'd like to increase efficiency, but only if I can do it without tripling my cost for the LED driver circuit.
The Bijunction transistor source circuit seems like it may be pretty cheap to assemble also, as do op-amps if using a cheap one.. but I can't seem to find any good commentary on if I am actually going to gain anything other than grief and cost to go to a "better" current source for power LED's and laser diodes. I'm also a bit confused on dissipation.. I assume that transistors would need to have sufficient power dissipation just like the LM317, in which case a regulator probably has higher ratings than comparably-priced transistors (thinking 2n3904, 2n2222, etc) when coupled with the other components. The LM317 does have the advantage of only being two components.
The circuits referenced are from http://en.wikipedia.org/wiki/Current_source
, but other information seems scattered and confusing. I'm sure there's expensive and difficult circuits that can do it.. I'm more interested in cheap and simple than necessarily doing it "The right way"... in other words, if the efficiency gain of 5% costs $10, it's not going to be worth it to me to implement it. Other than it's wastefulness, is there anything particularly BAD about LM317 current sources?