AN2708 Datasheet, PDF (1/42 Pages) STMicroelectronics – 2X36 W digital dimmable ballast with L6574 and ST7FDALI

AN2708
Application note
2X36 W digital dimmable ballast with L6574 and ST7FDALI
Introduction
This document describes a high-efficiency, high power factor, low THD and digital dimming
electronic ballast designed to drive 2X36 W T8 tube lamps.
The system consists of three main blocks:
The high-frequency ballast includes an active power factor correction circuit based on the
L6562 for universal input voltage as well as a ballast control circuit based on the L6574. The
digital dimming is performed by interfacing the ST7FDALI microcontroller with the analog
half-bridge driver.
The DALI control unit is dedicated to address the slaves, to display the lamp status and to
send the dimming commands. This unit is provided with a keyboard which allows setting
different dimming scenes over a wide range (5-100%) as well as putting in standby and
restarting the ballast. The DALI communication protocol includes single and group mode, as
well as broadcast mode to address the slaves.
The AC-DC adapter is based on the VIPer12A-E. This is an offline double-output isolated
power supply in DCM flyback configuration. The outputs are set for 20 V to supply the
communication bus and for 5 V to supply the MASTER microcontroller.
The three blocks are described in detail and their performances are shown. In addition some
of DALI basics are explained.
March 2008
Rev 1
1/42
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