Halogen to LED Desk Light conversion

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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.
Hardware
  • Desk light enclosure with 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.
Downloads
  • L5970 App Note (Mostly as an example of a driver that can be built with a typical Switch Mode Power Supply controller).
Schematic
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LED Module with one lens. 20 mm was the perfect diameter for the Sparkfun PCB.
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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.
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Perfect fit, now with a bunch of unnecessary warnings. Lenses glued in place with clear RTV Silicone (almost as useful as duct tape).
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Driver hanging in free air. Cardboard backing attached with double-sticky foam tape (another super useful item) to prevent shorting. Barely gets warm.