Total Newbie's First Build


Newly Enlightened
Dec 3, 2022
Lamberton, Minnesota
I'm working on building a drop in pill that I can use in both T20 and T50 IR illuminators. It will need to be compatible with 1 and 2 cell setups. I want as much output as I can get while extending battery life as much as possible.

I have brass pillars, 2 different BD39 drivers. Emitters are ordered, awaiting delivery.

Before I start assembly, I wanted to check in with a more experienced group to be sure I'm matching components properly. I don't want to over drive the emitter and have it fail prematurely. Also, as battery life is important, I want to use a driver that is very efficient.

I solder and have a good working knowledge of electronics as a hobbyist, but LED's and drivers are new to me. I've tried to locate the information by browsing through the forum threads, with little success.

If there is a thread that can explain the concepts used while matching, please send me a link.


Flashlight Enthusiast
Jan 22, 2004
Pleasanton (Bay Area), CA, USA
It has been a while since I built up some lights.

I did a lot of things incorrectly, but one thing that I did do right is to first built up a prototype on a piece of plywood before trying to built it into a light body.

In general LEDs are constant current devices, so ideally you want to use a controller / driver that allow real management of the current. One place to buy a true constant current driver that I know of is taskled, but there are also others.

Then there are pseudo constant current controls, for example you can use a simple resistor matched to the Vin - Vf of the led to make a sort of / not quite but some times good enough constant (ish) current driver if the voltage drop is not too much.

Some "drivers" are a step up from this and are essentially a variable resistor that helps to compensate for the changing Vin as the battery depletes during discharge. I am not certain, but I think that the kai approach is this one.

Some drivers use PWM to manage current (on average). Essentially they turn the power on / off rapidly to sort of average out the current going through the LED so that the led is driven (on average) the right amount.

The more sophisticated drivers really convert the excess (Vin x current )into a (lower Vin x more current) using an inductor, resulting in higher efficiency / longer run times. That is what you find in higher quality drivers like the Task led types.