Constant-Frequency Magnetically Controlled Universal Ballast With SoS Compliance for TL5 Fluorescent Lamps

This paper presents the development of a universal electronic ballast for TL5 lamps. The intent is to efficiently operate the maximum number of TL5 lamps with different power ratings at nominal power, using a resonant variable inductance, provided by a magnetic regulator, while maintaining the switching frequency constant. A microcontroller and additional digital circuitry are used to command a dc-dc buck converter to supply the necessary dc control current to the magnetic regulator and to regulate the switching frequency of the half-bridge resonant inverter that supplies the lamp. The selection of the resonant capacitance is done in order to comply with the SoS limits established for each lamp. Experimental results with lamps ranging from 14 to 49 W, operating with high efficiency and high output, are presented in this paper.