I am using an ADP2504 switching regulator as an LED current regulator. There might be parts that are more suitable to the application but the ADP2504 is attractive because it is in an especially small package.
The LED anode goes to the Vout pin and the LED cathode goes to the VFB feedback pin which is connected to a 1 Ohm sense resistor to GND. The regulator feedback should force the VFB input to 0.9V
I've simulated the circuit in LTSpice and have built the circuit on a PCB with a full ground plane. I have about 4" of twisted wire from the regulator to the LED, and a similar length to the power supply. The circuit works but doesn't regulate well and is sensitive to input voltage changes, regardless of whether it is running off a bench supply or off a single lithium ion cell.
