When I go to the big box stores I usually stop look up the flashlights to see what’s new. I often see a palm sized flashlight with 27 LED’s, 24 of them on the flat side. The case is rounded on the corners and is typically yellow and black; the price is about $4 or $5. A few years ago I bought one to remove the LED’s but I never got around to it. Instead I drove a hole in the case and ran two wires out so instead of three AA cells, the light could be connected to an external power supply. I used it for a while on a high powered Joule thief. I disconnected it from the Joule thief and connected it to a power supply. I liked the beam pattern because it spreads out to about the size of a page at a distance of 2 to3 feet. I just recently made a book reading light but I thought this one would make a good one too.
My first thought was how to power this light. 3 AA cells make 4.5 volts so a good choice would be a 5 Volt power supply. I connected the lights 2 a power supply turned it up to 4.50 volts. The current was about 400 milliamps, which is about 16.7 milliamps per LED. This is a very good point to run these LEDs.
The light already has an internal resistor so the problem is to drop the voltage from 5 volts down to 4.5 volts. I put 1N4003 in series with the power supply but the voltage went down to 4.2 volts. I tried a shot keep dialed shot key diode but the current was over 400 milliamps. I tried several more diodes and finally found A 1N5403 3 amp diode that drops about .7 volts and the current is about 390 milliamps. It got slightly warm after awhile but it’s only dissipating .3 watts. This one looked like it will do a good job.
My next task is to find a 5 volt wall wart adapter that has the correct plug, or else cut the plug off and put something else on it. I have some adapters have very tiny plug and I know I can’t find a jack for it.
