This document describes the working principle and application methods of LEDs, and presents LED driving application examples using ST DC-DC converters.
This application note describes the main applications and driving methods for Light Emitting Diodes (LEDs). It explains that LED brightness is proportional to forward current and discusses the necessity of using constant current sources to ensure brightness matching between different LEDs.
The document presents several application ideas using STMicroelectronics DC-DC converters, categorized into DC bus supply applications (using L497xD, L597xD, and L6902D families) and battery-powered applications (using the L692xD family). It provides specific circuit schematics and efficiency tables for driving various numbers of high-current white LEDs in series.
| L5970D Output Current | up to 1A |
|---|---|
| L5970D Input Voltage Range | 4.4V to 36V |
| L5970D Feedback Voltage | 1.23V |
| L4973D Output Current | up to 3.5A |
| L6902D Sense Resistor Voltage | 100mV |
| L6920D Operating Input Voltage | down to 0.6V |
White-blue LEDs have a typical voltage drop of 3-4V.
Green-red-yellow LEDs have a typical voltage drop of about 2V.
The L6902D allows for a minimum voltage drop of 100mV across the external sense resistor.