Roundup: Driving, dimming, and protecting LEDs – A list of DIY circuits and articles for LED power and control.
An LED constant current source (PDF) – This simple design drives LEDs in a series/parallel arrangement. The circuit uses an LM317L plus a transistor on each parallel string to prevent current-overload if one parallel string fails open.
Why drive white LEDs with constant current? – Includes a good background that discusses different ways of powering LEDs and the advantages of constant current sources.
Constant current LED driver circuit uses LM334 plus one transistor to drive a series string of LEDs.
This constant current source design on Instructables.com uses a two-transistor design to power a series string of LEDs. An NPN transistor controls an N-channel power FET.
Here’s another constant current driver schematic using two transistors. This one provides buffered control of the LED.
This is a constant current LED driver design that delivers high current (200 mA). It is designed around an NCP3063 On Semi voltage regulator that has a constant current mode. The designer claims a low parts cost; Efficiency should be around 70%.
This IC plus a capacitor and resistor (PDF) provides a constant current drive for up to four strings of LEDs. Max current per string is 150 mA and the outputs can be paralleled for higher currents and fewer strings. It supports cathode voltages of 1.0 to 16V.
Need a battery-powered design? Single- or multi-cell LED driver (PDF) can drive LEDs with currents up to about 55mA with a maximum output voltage of 20V. The three terminal device operates from a single cell down to 0.9V and requires only an inductor. Efficiency is about 85%.