Why regulate the voltage from your supply when you really need a controlled current to drive an LED? Any regulator is less than 100% efficient, and the losses increase as more current is drawn. It looks like the circuit in this application note would allow you to skip the voltage regulator and thus avoid massive losses. You would still use a regulator for the µC part of the circuit where a steady voltage is needed, but the LEDs could be driven independently. Unfortunately, the circuit as shown has way too many parts, but I have a feeling that the basic idea can be used in a much smaller circuit after careful study. In the last several years, I’ve designed USB-powered boards with almost 200 LEDs, and I wish I had known about this technique to squeeze every last ounce of energy out of the limited 2.5 W USB supply.
This LED driver reference design drives a 700mA constant current to a single string of LEDs with forward voltages up to 60V. The design allows PWM dimming based on supply chopping. The input power supply is chopped on and off at 300Hz to 1kHz frequency to achieve LED brightness control. The driver uses a fixed-frequency boost converter, controlled by the MAX16834 LED driver. This unique reference design limits the input inrush current to negligible levels without compromising either the input or output filtering. Design schematics and test results are provided.