A constant power control digital electronic ballast for metal halide lamps

A constant power control digital electronic ballast for metal halide lamp (MHL) is presented in this paper. It is constructed by a three-stage power converter and drives the MHL with a low frequency square-wave to eliminate acoustic resonance. The circuit construction of the ballast is detailedly analyzed in this paper. Control and protection circuit based STC12C5410AD MCU is also designed to ensure stable operation of the MH lamps. According to V-A characteristics of MHL, a corresponding control method is proposed to actualize successfully ignition for MHL´s startup, and to ensure the lamp operating safely and stably through detecting working condition of the ballast. The flow chart of software design is also given. Finally, a laboratory prototype of 70-W electronic ballast is implemented. Experimental results show that all electrical parameters satisfy the design requirements.