Halogen to LED Desk Light conversion

Hacked Desklamp showing how bright it is

A new life

A bunch of miscellaneous parts went into this hack that I use to light my soldering area. The interesting aspect of this hack is the fan connected in parallel with the LEDs to eliminate the need for another power supply. The forward voltage across the LEDs is high enough to let the fan run at an acceptable rate and it requires only a small current leaving the rest for the LEDs. Although the amount of light generated by this hacked fixture is less than the original halogen version, tight focusing of the beam gives a very usable result at much less power and wasted heat.
  • Desk light enclosure with a big honking 12 VAC transformer in the base.
  • Constant Current Driver module. I used a ST Microelectronics L5970 evaluation module configured to drive about 700 mA but any constant current module that can take AC input (or is fronted by a rectifier and filter) should work.
  • An old (and now obsolete) Sparkfun 3-LED module using Luxeon Rebel daylight LEDs.
  • Three 20 mm Carlco 10193 narrow focus LED lenses glued onto the LED module. I got mine from Mouser.
  • A small 12 VDC fan designed for CPU module cooling mounted to the rear side of the LED module.
Desklamp circuit diagram showing fan in parallel with 3 LED string
LED array showing lens
LED Module with one lens. 20 mm was the perfect diameter for the Sparkfun PCB.
LED array mounted with fan
Close-up of the "LED Engine" mounted to the existing Desk Light's faceplate. I removed the protective glass shield that covered the original halogen bulb.
LED array in fixture where halagen light went - its a perfect fit
Perfect fit, now with a bunch of unnecessary warnings. Lenses glued in place with clear RTV Silicone (almost as useful as duct tape).
LED driver taped to lamp arm
Driver hanging in free air. Cardboard backing attached with double-sticky foam tape (another super useful item) to prevent shorting. Barely gets warm.