Electronics: Building a Constant Current LED Driver
Build time: 1-2 hours
Tools needed: Soldering iron
electronicsdiyguide
High-power LEDs (1W+) will draw more and more current as they heat up, leading to 'thermal runaway' and failure.
1. The LM317 Method
Use an LM317 voltage regulator in 'Current Mode'.
2. Calculate the Resistor
R = 1.25 / Desired Current. For a 350mA LED, use a 3.6 Ohm resistor.
3. Wiring
Connect the output pin of the LM317 to the resistor, then to the LED. The adjustment pin also connects to the LED side of the resistor.
4. Heat Management
Both the LM317 and the LED will get hot. Mount both to a heatsink using thermal paste to ensure long-term stability.