Constant-current driver for lantern upgrade?

While buying some other items, I ran across a disc-type hanging lantern, and decided "what the heck". [My tent is on the small side, I'm fairly tall and I'm tired of bonking my head on the lantern I've been hanging in the top of the tent.] 48 white 5mm wide-angle LEDs, run direct-drive in parallel from 3AA cells. It's quite bright, nice even light - but even with the relatively flat discharge of NiMH cells, I found myself thinking that current regulation would be nice - and given how bright it is, perhaps even a lower setting. I've never modded anything this way before, and I'm not even sure whether I should be looking for a boost-only or a buck/boost driver. (If I were planning to run 14500's in it, then I know I'd go for a buck only driver - but I don't plan to get that exotic.) I don't know what the Vf of these LEDs isand thus how much voltage "headroom" I have on 3 NiMH AA's.

Ideally, I'd like a top output of 1000-1200ma and one or two lower modes, nothing more complicated with flat regulation until my Eneloops give up. Probably best to start out with "low", though that's not essential. I've browsed a bit on DX and used the driver database at Aqualab but I'm still unsure. Here are some photos of the interior, to give an idea of how much space there is (or isn't) to work with:


Any suggestions on how to accomplish what I want to do are most welcome!

I have built switching regulators and one with 11-15V in and 14.2V out was about 85% efficient but 3.6V is not much to work with. It takes a fair amount of time to make a switcher from scratch and it is generally better to buy one off the shelf it there is one available. However, there is a much simpler and cheaper way of reducing the output slightly providing that 3.0 V will give the desired result. Two good alkaline cells should give 3.0 V to test.

When I want to reduce the output of three NiMH cells to around three volts I use a silicon power diode of about twice the wattage rating of the lamps in series with the battery. The diode will drop the voltage by about 0.6 V (about 0.4V for germanium) Usually I use a double throw switch that switches the diode in or out to give the choice of about 3.0V or about 3.6V respectively to the load.

Hi Bikerbear! I have used DX part# 6190, 5-Mode 1000mA 7135 Circuit Board for Cree and SSC Emitters, in several lights using 3 NiMH batteries. Although it comes as a 5-mode, it has several other modes that are enabled easily. Low, medium and high, for example, at 80ma, 350ma, and 1050ma. At $3.19 it is a great regulator. Small too, so it should fit in your lamp.

Cheers,
Jeff