Constant Current Circuits
Current LED Driver 5
December 13, 2010
LEDs are current driven devices.
The light they produce is proportional to the current flowing though them.
One way to maintain a fairly steady light output is to keep the current through
the LED fixed, even as the supply voltage may change. A classic way to do
this is shown below. This works fairly well but it has two weaknesses.
It requires a 0.6v voltage drop across the current shunt resistor and due to the
base-emitter voltage temperature sensitivity, the current increases with