Use of Auxiliary Resonant Tank to Ensure Soft-Switching in High Frequency Electronic Ballasts for Metal Halide Lamps

An auxiliary resonant tank-protected high-frequency electronic ballast and a pseudo-inductive soft-switching concept are proposed in this paper. Based on the steady state analysis of the series resonant converter, the operational characteristics of the ballast circuit for metal-halide (MH) lamps under different conditions are examined, and then potential hazards to the ballast circuit are addressed. To avoid those dangers, an auxiliary resonant tank is used for protecting the ballast circuit under all operations. With this auxiliary resonant tank operating in either inductive or pseudo-inductive modes, soft-switching can be ensured in the electronic ballasts. Feasibility of the proposal for the ballast circuit is verified by analytical and experimental results obtained from the 150-W prototype ballast for a MH lamp