June 2010

Doc ID 16181 Rev 2

1/27

AN3040

Application note

STEVAL-ILB008V1 4 x 18 W/T8 ballast driven by L6585DE

Introduction

This application note describes a demonstration board able to drive a 4 x 18 W linear T8

fluorescent tubes.

The ballast is controlled by the new L6585DE IC that integrates the PFC and half-bridge

control circuits, relevant drivers, and the circuitry that manages all the operating phases

(preheating, ignition and run mode) of the lamp. Protections against failures such as lamp

disconnection, anti-capacitive mode and PFC overvoltage are guaranteed and obtained with

a minimum number of external components. In addition to the description of the circuit and

design criteria, this document provides a short overview of the ballast performances.

Fluorescent lamps are driven more and more by electronic ballasts rather than by

electromagnetic ballasts, primarily because fluorescent lamps can produce around 20%

more light for the same input power when driven above 20 kHz instead of 50/60 Hz.

Operation at this frequency also eliminates both light flickering (the response time of the

discharge is too slow for the lamp to have a chance to extinguish during each cycle) and

audible noise. Electronic ballasts consume less power and therefore dissipate less heat

than electromagnetic ballasts. The energy saved can be estimated in the range of 20-25%

for a given lamp power. Finally, the electronic solution allows better control of the filament

current and lamp voltage during preheating with the unquestionable benefit of increasing the

average lamp life.

Figure 1.

4 x 18 W T8 ballast demonstration board

www.st.com