ST AN1756 Application note

AN1756

Application note

Choosing a DALI implementation strategy with ST7DALIF2

Introduction

This application note describes how to choose a DALI (Digital Addressable Lighting Interface) implementation strategy using the ST7DALIF2 microcontroller. As well as presenting topology options, this document also gives an introduction to the DALI standard with a description of the protocol and a list of advantages.

Please refer to Section 4 for a list of additional documents referenced in this application note.

March 2009

Rev 3

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Contents	AN1756

Contents

1	High-frequency tube lamp ballast applications . . . . . . . . . . . . . . . . . . .		3
2	Choosing an implementation strategy . . . . . . . . . . . . . . . . . . . . . . . . . .		4
3	DALI standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		6
	3.1	Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	6
	3.2	DALI standard protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	6
	3.3	DALI system advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	7
4	References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		8
5	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		9

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AN1756	High-frequency tube lamp ballast applications

1 High-frequency tube lamp ballast applications

Basically, a HF-TL ballast converts the 50-60 Hz AC Line input or a DC voltage to a high frequency output, usually in the range of 25-125 kHz. A rectifier block and a DC to high frequency inverter usually make up a ballast (please refer to 1 in Section 4: References).

Voltage fed series resonant half bridge inverters are currently used for fluorescent lamps. This topology allows to easily operate in Zero Voltage Switching (ZVS) resonant mode, reducing the transistor switching losses and the electromagnetic interference (please refer to 2 in Section 4: References).

The half bridge of the inverter can be controlled in different ways with different ICs:

●Half-bridge controller like, for example, the L6574.

Figure 1. Typical topology with a half-bridge controller

●Half-bridge driver like, for example, the L6384 + some kind of control.

Figure 2. Typical topology with a half-bridge driver

What is the difference between a half-bridge driver and a half-bridge controller?

A driver is “just” able to drive the floating (high side) transistor of a symmetric half bridge inverter, from a Pulse Width Modulation (PWM) signal. The controller also includes some form of oscillator, usually tunable by using a few external components (resistor, capacitor).

Varying the switching frequency is the mainly used control principle. This allows the current in the lamp, and therefore the output power to be modulated (please refer to 2 in Section 4: References). So the lamp can be dimmed and input voltage variations can be compensated.

To know more about high frequency tube lamp ballast applications, please refer to 2 in

Section 4: References.

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