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AN880 Datasheet(PDF) 1 Page - STMicroelectronics |
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AN880 Datasheet(HTML) 1 Page - STMicroelectronics |
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1 / 14 page  THE L6569: A NEW HIGH VOLTAGE IC DRIVER FOR ELECTRONIC LAMP BALLAST by G. Calabrese and T. Castagnet INTRODUCTION Electronic lamp ballasts are now popular in both consumer and industrial lighting. They offer power saving, flicker free operation and reduced sizes. Improvements to the light control and cost reduc- tion of the ballast will broaden their market accep- tance. Today designers focus on reducing the cost of the ballast, but also work to add features to the bal- last like saving energy by dimming the light, or in- creasing the life time with better preheat and pro- tections. Such requirements have contributed to the development of dedicated high voltage con- trollers like the L6569, which are able to drive the floating transistor of a symmetric half bridge in- verter. This device is a simple, monolithic oscilla- tor-half bridge driver that allows quick design of the ballast. HIGH VOLTAGE IC DRIVERS IN BALLAST AP- PLICATIONS The voltage fed half bridge Voltage fed series resonant half bridge inverters are currently used for Compact Fluorescent Lamp ballasts (CFL), for Halogen Lamp transformers, and for many European Tube Lamp (TL) ballasts. This simple converter is preferred for new de- signs, because it minimizes the off state voltage of the power transistors to the peak line voltage, and requires only one resonant choke. In addition this choke protects the half bridge against short circuits across lamp terminals. However overheat- ing and overcurrent occur during open load op- eration. The inverter robustness must be im- proved, or some protections are required. The half bridge inverter operates in Zero Voltage Switching (ZVS) resonant mode [1], to reduce the transistor switching losses and the electromag- netic interference generated by the output wiring and the lamp. Fully integrated ballast controllers By varying the switching frequency, the half bridge inverter is able to modulate the lamp power. However most current designs use a sin- gle frequency with a saturable pulse transformer (see fig. 1) to drive the transistors. This type of design has a higher component count, a higher tolerance on the switching frequency, and it can- not adjust the lamp power. The only way to design a cost effective, compact and smart control of the lamp is to use a dedi- cated I.C. that is able to drive the upper transistor of an symmetric half bridge inverter. Such control- lers require a high voltage capability for the float- ing transistor driver [2]. MOSFETs are preferred over Bipolar transistors as power switches be- cause their gate driver requires a lower supply current and a smaller silicon size [3]. February 2003 ® Figure 1: CFL series resonant half bridge inverter. 2 µs/dv ; 50 V/dv ; 0.1 A/dv ID VDS RF LVG GND GND GND Figure 2: Current and voltage of the STD3NA50 MOSFETs when driven in ZVS with the L6569. AN880 APPLICATION NOTE 1/14 |
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