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5W luxeon led

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I suspect that is not a Luxeon since I do not see that he even claims it to be one.

While you can get 180Lm out of one, that is at 25C junction temp. to find your actual light output you need to calculate die temp at thermal equilibrium and look at the graph on the spec sheet.

you might, rabbit, you might. (use that chip)

Dan
 
That current regulator chip will do the job, however the hard part is obtaining the current feedback resistor that the chip requires to determine the constant current amount be supplied to the LED. We are talking milliohm resistor values, which you will most likely not be able to purchase but rather have to fabricate and measure accurately.

Lefty
 
The tiny chip cannot dissipate much heat. So the difference between the total LEDs voltage and the supply voltage must be low. Then the supply voltage must be regulated. The example in the datasheet shows a 12V supply and three 3.6V LEDs so there is only 1.2V across the chip and its heating when the current is 1A is "only" 1.2W minus the 0.1W in the current-sensing resistor.

The chip is not efficient since it wastes a lot of supply power by making heat.
Look for a switching current regulator that will be efficient.
 
You can use a much higher valued resistor, up to 5 ohms (5 watt), and a series pass transistor in common-emitter mode. Control the current through the transistor (somethiing like a good old TIP31 TO220 on a heatsink) with an op-amp comparing the drop on the resistor to an adjustable reference (potentiometer.)
I have done this with good results using a 12-volt supply. Don't get all wimpy about burning a little power; that resistor will protect your Luxeon LED.
It may not be a Luxeon, but the Chinese are turning out some pretty good copies.
 
As Uncle $crooge stated you need a switching type current regulator if you want the best efficiency. It's probably cheaper, and certainly a lot easier, to buy one ready-made, such as a Buckpuck, rather than try to build one yourself.
 
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Homer,

If you need 'EFFICIENT' then are you using batteries? If so do not use the STCS2A. What voltage do you have? 3V?, 6V? 12Volts?
 
The LM3404 is right if:
The battery voltage is greator than 6 volts.
The LED is 3 watts.
 
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