Even More Hippies on your Head!
When I bought my 1W Luxeon , I also succumbed to temptation and bought its big brother, the 5W. After getting the 1W running as a backup commuter light, it was time to build the Shiny! one.
5W Luxeons come from a few different bins, which have different required voltages and output colours. The one I ended up with needed 6.8V, at a constant 700mA. I'd originally planned to build a switchmode power supply to run this off my various 12V batteries, but one day I happened across a bunch of 4AH NiCD D cells from emergency lights. The condition was unknown, but I picked up 8 of them for $15, which isn't too bad. In the end, I did have a dud cell, but I've still got the 7 cells required to run a regulator along the same lines as the one in my 1W Luxeon.
This regulator is based on a constant current NiCd battery charger that was in the back of the old Dick Smith cattledog. The 1k resistor lets around 10mA through to the MOSFET gate and the 1N4148 diode. The voltage drop across the diode at this current is around 650mV. That means the gate is held at 650mV, which holds the source at 650mV. Since there is a 650mV drop from here to ground, the value of Vref controls the current through the system. A pair of 1.5 ohm resistors n parallel gives a measured 705 mA through the LED.
To allow me to go back to my original plan, there is no regulation in the LED assembly itself. Instead I've mounted the regulator inline in an old film canister. The input uses a DC plug I had floating around, while the output is a hard drive power connector from a PC power supply. To provide the matching female connector I cannibalised a PC fan that had a a matching piggyback connection. To increase the current capacity, I've run parallel connections to both grounds and both the 5 and 12V connections. I don't think I'll ever be silly enough to put this into a PC... i
A LED this big needs a big heatsink. I'd originally found a 32mm PVC endcap that fit the reflector quite well, but hadn't worked out how to hold the LED in. Further contemplation allowed me to become shamelessly inspired by Michael Carden . I found a whopping great T0-3 heatsink in a shop in town for $4, and used nylon bolts to clamp the LED to it.
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