June 2009

Doc ID 14904 Rev 1

1/25

AN2811

Application note

3.5 W non-isolated offline constant-current LED driver

based on VIPER17

Introduction

High brightness LEDs are becoming a prominent source of lighting. Compared to

conventional incandescent bulbs, high brightness LEDs (light emitting diodes) have

advantages in higher light efficacy, much longer life and faster reaction time in a smaller

profile. Since LEDs cannot sustain high voltage stress directly from an AC source, providing

a reliable constant-current source to drive LEDs becomes fundamental. This solution

provides even luminosity, reliability, the highest efficacy and the longest operating life for

LEDs.

This application note describes the non-isolated offline constant-current driver based on the

VIPER17HN (high frequency version). This solution operates with an AC line input range

from 176 V to 264 VAC and provides 500 mA constant current from a 7 VDC source. It can

illuminate two LEDs in series.

This device is an offline converter with an 800 V rugged power section, a PWM control,

twice the level of overcurrent protection, overvoltage and overload protections, hysteretic

thermal protection, soft-start and also safe auto-restart after any fault condition removal.

The embedded brownout function protects this switch mode power supply in case the main

input voltage falls below the specified minimum level for this system.

Figure 1.

STEVAL-ILL017V1 demonstration board

www.st.com