Re: Custom Luxeon III (Automotive Related) Questio
TopazDave:
Pardon the novella - I got carried away. I ought demand a small tribute from Lumileds for these...
I think you'll find that off-the-shelf drivers are too costly for what you want to do - unless you can score a sweet quantity discount direct from the manufcaturer.
Most current supply designs will be able to run 2-3 Luxeons in series from a nominal 12V supply. If you need to run more, you can always run strings of 2-3 in parallel.
A Luxeon I will dissipate up to a nominal 1.25W, and a Luxeon III will dissipate up to a nominal 3.8W - both depending on the characteristics of the specific emitter. Emitters with lower forward voltage (Vf) dissipate less power and generate less heat. You might be able to negotiate for specific Vf bins from a supplier or Lumileds directly if your quantities are high enough.
Generally, you want to throw more heatsink at a Luxeon and not less. Heat kills solid-state electronics like nothing else.
Maximum Junction temperature:
Luxeon I: 120°C
Luxeon III: 135°C
Junction temperature isn't useful for most of us since we're going to measure the temperature of the outside, on the emitter "slug". If you're more up on thermodynamics than I am, you can determine the maximum acceptable temperature at the slug using thermal resistance values:
Luxeon I emitter: 15°C/W
Luxeon I star: 20°C/W
Luxeon III emitter: 13°C/W
Luxeon III star: 17°C/W
I don't know the specifics of your application, so I don't know if you'd prefer the "star" or bare emitter.
Stars are typically used for applications where the LED will be some distance away from the power supply, the distance will vary, or conditions are a bit too harsh to locate the driver with the LED. A star offers a built-in heat spreader if the LED is to be mounted to a metal surface or larger heatsink. Stars are better suited to manual assembly outside of an electronics fab environment due to their superior mechanical robustness versus stars and ease of "field installation."
Emitters are better for situations where the LED will be used on a driver board or in an electronics fab environment. Emitters almost always require heatsinking to operate at higher rated currents and must be handled with greater care than stars. Emitters offer more versatility when it comes to external optics or "packaging" into housings & optical assemblies.
Lumileds has extensive documentation for the Luxeon series. I'd suggest you check out the following datasheets (might require registration or anonymous sign-in):
PG01 Luxeon Product Guide
DR02 Luxeon for Flashlight Applications (not entirely relevant to what you're doing, but there's good information in there)
DS25 Luxeon I emitter datasheet
DS23 Luxeon I Star datasheet
DS45 Luexon III emitter datasheet
DS46 Luxeon III star datasheet
AB11 Luxeon Electrical Drive information
AB05 Luxeon Thermal Design Guide
My own distilled version of Lumileds' official binning guide
