Design of Resonant Inverters for Optimal Efficiency Over Lamp Life in Electronic Ballast With Phase Control

The paper presents the design guidelines of phase controlled resonant inverters to drive high intensity discharge lamps. Considering the variation of the lamp resistance over its lifetime, the resonant phase is determined and the condition of minimum phase lag is imposed to minimize the current through the circuit. The optimum input voltage is analyzed according to phase lag, frequency variation, and control complexity. A design procedure is presented and experimentally validated with results from two electronic ballast designs operating from 300-V and 400-V dc bus and driving a 150-W high pressure sodium lamp