Resonant Converter as a High Pressure Sodium Lamp Ballast

Summary Analysis and design of a single-stage electronic ballast with unit power factor are presented in this paper. The proposed single-stage ballast is the combination of a boost converter and a full-bridge series-resonant parallel-loaded inverter. The boost semi-stage working in the discontinuous conduction mode functions as a power factor corrector and the inverter semi-stage operated above resonance is employed to the ballast lamp. The fundamental approximation is used to design the inverter at steady-state. A novel control method by resonant current allows to the bridge switches operating in points where the commutations are optimum and the reactive energy that the inverter handles is nil. The proposed lamp ballast can save a controller, reduce size and possibly increase system reliability over a conventional two-stage system. Experimental results from a lab prototype are used to verify the design procedure.