A high efficiency MHD lamp ballast with a frequency controlled synchronous rectifier

In this paper, in order to develop a simple and high efficient ballast without an external ignitor, a half-bridge type ballast with a coupled inductor and a frequency controlled synchronous rectifier is proposed. The internal LC resonance of the buck converter is used to generate a high voltage pulse for the ignition, and the coupled inductor filter is used for steady state ripple cancellation. Also, a synchronous buck converter is applied for the DC/DC converter stage. In order to improve the efficiency of the ballast, a frequency control method is proposed. This scheme reduces a circulation current and turns off loss of the MOSFET switch on the constant power operation, which results in increase of the efficiency of the ballast system about 4%, compared to a fixed frequency control. It consists a 2-stage version ballast with a PFC circuit. The results are verified with hardware experiments.