AN2811 Datasheet, PDF (1/25 Pages) STMicroelectronics – High brightness LEDs are becoming a prominent source of lighting

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


June 2009
Doc ID 14904 Rev 1
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1/25
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