I'm trying to connect a 3 Watt luxeon to my Arduino, but the whole project is driven off of a 9 volt supply. I'm using a 7805 atmega168 and related hardware, but the LED supply will be 9V.
I've tried an NPN transistor with 9V to LED to resistor to collector, emitter to ground. But with the Arduino IO limited to 5V and the LED only dropping 3.6V, I can't get the transistor into full saturation and I can only pump about 300 mA through the LED.
Anyone have any suggestions? Until yesterday, I didn't know that the emitter-ground volatage was limited by the base-emitter voltage. I supposed it would work with a couple of 1N4004's in series with the LED to drop the voltage, but that just seems clunky to me.