Modeling and control of an electronic ballast based on differential connection of Flyback converters

This paper presents the ac model and digital control of an electronic ballast topology based on the differential connection of Flyback converters. The electronic ballast supplies a 70 W high pressure sodium lamp with low frequency square waveform in order to avoid the acoustic resonance phenomenon. The modeling results in the transfer functions that relates the lamp voltage and current with the input voltage and switches duty cycle. A low cost microcontroller with fixed-point support was used to implement the digital control strategy. This strategy consists on a fast loop for current control and an outer slow power loop for maintaining the lamp power constant during its useful life. A prototype was implemented in order to verify the proposed controllers.