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5W Cree Led to 12V. How?


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I have LED: CREE XR-E Q5 high power LED Light Emitter White Aluminum base 5W XLamp

Series: XLamp XR-E 7090
Guaranteed minimum Luminous Flux order codes up to 114 lm in white at 350 mA (equivalent to 1W)
Forward Voltage @ Test: 3.3V
Viewing Angle: 90°
~6000K-7000K cool xenon white color temperature
Maximum drive current: up to 228 lm at 1000 mA (~equivalent to 5W)

I read that for LED needs current limiter circuit. I find LM 317 calc and enter current 1A and Voltage 3.3V:
I see that i need resistor 1.3 Ohm. But I need connect my LED to 12V. And don't understand how I must connect it's.
I need two LM317? First LM317 for lower the voltage to 3.3V.  And two LM317 for current limit?
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There's an error in the information. You'll need 1.5A to get 5W with a forward voltage drop of 3.3V.

You don't have to worry about the voltage which is self-limited by the LED. The current just has to be limited so a constant current source is all that's required.

The LM317 won't really cut it and is only something one would use if they had nothing else to spare. The efficiency at 12V with a 3.3W LED is a pitiful 27.5% and asking it to dissipate >8.7W is a lot, even with a good heat sink.

You can buy purpose made ICs and modules for this. Here a few parts which would do what you want:


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