AN2459 Datasheet, PDF (1/35 Pages) STMicroelectronics – Digital Power Factor Correction for Tube Lamp Ballasts

AN2459
Application note
Digital Power Factor Correction for Tube Lamp Ballasts and
other digital power supplies controlled by an 8-bit microcontroller
1
Introduction
The electronic ballast market has undergone dramatic changes over the last few years. It
has moved from full analog, very differentiated applications made by a collection of drivers
and controllers, where use of custom ASICs was widespread, to a couple of standard
platforms.
The basic building blocks are still the same. They include a power factor corrector stage and
an inverting high voltage stage (Figure 1). On the one hand, analog platforms are targeting
the low cost/basic performance applications. Their main drivers and controllers are widely
used and well known ICs such as Power Factor Correctors (L6561/2/3) and High Voltage
Ballast Controllers (L6569x/ L6571x/ L6574). On the other hand, a new digital platform
concept has gained more interest and acceptance. A microcontroller with a simple Half
Bridge Driver (L638x) has replaced the ballast controller. The Half Bridge Driver is used
mainly for high-end applications, especially where the microcontroller has to deal with
communication tasks (e.g. using the Dali protocol).
STMicroelectronics' digital ballast reference design STEVAL-ILB002V1 introduces a safe
operating Power Factor Controller (PFC) and Ballast Controller. Even with relatively simple
microcontroller firmware routines, the results for power control and ballast protection are in
line with advanced analog controlled ballasts, while adding flexibility, for example, the
possibility to drive a wide variety of lamps, or to easily introduce different protection
schemes.
This application note deals in detail with the first block of the digital ballast, which provides
stable DC bus voltage for the halfbridge in all load conditions, as well as controlling the input
current shape which fulfills IEC standards (6.: IEC 61000-3-2 "Electromagnetic
compatibility".).
The final description of the digital ballast - the lamp control block - will be described in detail
in a separate application note.
Figure 1. Digital ballast scheme
Input Filter
8- Bit
Microcontroller
ST7FLITE19B
Power
Management Unit
L6382D5
January 2007
Rev 1
1/35
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