Current Regulated Luxeon Star LED Driver

Overview

Using an LM317T adjustable voltage regulator with a current programming resistor is the basic concept of this project in order to get a constant current source to safely drive the Luxeon Star.

Explanation

The project is considered as cheap because the circuit itself is pretty simple with just a minor variation. The LM317 is conveniently thought as 1.25V voltage source where pin 2 is at 1.25V with respect to pin 1. The current programming resistor across the 1.25V source will always carry a current of 320mA due to the 3.9 Ohms value. Kirchoff’s current law requires that the current delivered to the load will be 320mA when a load is connected between ADJ and ground.

For the target design, the 320mA value was chosen because it is close to and comfortably beneath the rated 350mA for the Luxeon Star. With these values, the power dissipated in the current programming resistor is 400mA which would require a 1/2W resistor for the 320mA design. The power dissipated in the regulator will be dependent on the value of input voltage and this will require a suitable heatsink that will be necessary to provide cooling for regulator.