High efficiency metal halide discharge lamp ballast with an internal igniter and low ripple lamp current

This is a proposal for a half-bridge type metal halide discharge (MHD) lamp ballast with a coupled inductor and a frequency-controlled synchronous rectifier. To avoid using an external igniter, the internal LC resonance of a buck converter is used to generate a high-voltage pulse for the ignition. A coupled inductor filter is used for steady state ripple cancellation. This filter allows the MHD lamp to avoid the acoustic resonance phenomenon. To improve the efficiency of the ballast, a synchronous buck converter is used for the DC/DC converter stage and a frequency control method is proposed. This scheme reduces the circulation current and turn-off loss of the metal-oxide semiconductor field effect transistor (MOSFET) switch in the constant power operation, which results in an increase of the efficiency of the ballast system compared to fixed frequency control. A front-end power factor correction circuit is included in the ballast. This proposal zis verified with hardware experiments.