February 2008

Rev 2

1/14

UM0422

User manual

Constant current controller for high brightness LEDs

Introduction

The recent improvements in high power light-emitting diode (LED) technology with 100

lumens per LED chip and efficiency higher than that of incandescent lamps bring solid state

lighting close to reality. Light-emitting diodes (LEDs) have become very popular in the area

of general lighting as a replacement technology for low voltage lighting. Customers are

recognizing the advantages of using LED lighting which include long operating life, no fragile

glass, and low voltage DC operated.

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 are not sufficiently accurate nor efficient. It is well known that the brightness of LEDs

is proportional to the forward current. The best way to supply LEDs is to control the forward

current in order to get a good match of the output light. LED manufacturers specify the

characteristics (such as lumens, beam pattern, color) of their devices at a specified forward

current (IF) but they do not specify these characteristics at a specific forward voltage (VF). In

order to better control the LED current under several application conditions,

STMicroelectronics has developed the STCS1, a device which not only guarantees a

constant LED current but also provides useful features that make the device suitable for

different applications such as advertising signs, automotive interior and exterior lighting, and

emergency vehicle warning lights. This document describes how to use the STCS1

evaluation board. It includes a schematic diagram, bill of materials (BOM), and test data.

Figure 1.

STCS1A evaluation board

Table 1.

Device summary

Description

Order code

STCS1A evaluation board

STCS1ADEMO1

www.st.com