Buck high-brightness LED driver based on the ST1S10
step-down DC-DC converter voltage regulator

Introduction
High-brightness LEDs are becoming a prominent source of light because of their long life, ruggedness, design flexibility, small size and energy efficiency. LEDs are now available in higher and higher wattages per package (1 W, 3 W and 5 W) with currents up to 1.5 A.
At these current levels, the traditional means of limiting current with a resistor is not sufficiently accurate nor efficient. Today, single-dice, white HBLEDs capable of delivering up to 90 lm/W of light are available. A typical 1 W white LED delivers an optical efficiency of 30 lm/W, whereas a typical 60 W light bulb delivers 15 lm/W.
It is known that the brightness of an LED is proportional to the forward current, so the best way to supply LEDs is to control the forward current to get good matching of the output light.
LED manufacturers specify the characteristics (such as lumens, beam pattern) of their devices at a specified forward current (IF), not at a specific forward voltage (VF).
This application note describes how to implement a constant current control to drive high-brightness LEDs by a step-down DC-DC converter voltage regulator.
A switching regulator is the best choice for driving HBLEDs when high efficiency and low power dissipation are
required.
The circuit uses the ST1S10 high-efficiency buck converter configured to drive a single HBLED in constant current mode.
The ST1S10 is a step-down monolithic power switching regulator which needs few external passive components and it is capable of delivering 3 A.
An internal oscillator fixes the switching oscillation at 900 kHz, and it is possible to synchronize the switching frequency with an external clock from 400 kHz to 1.2 MHz.
This application note includes a schematic diagram, bill of material (BOM), and test data.