Arc stabilization in low-frequency square-wave electronic ballast for metal halide lamps

Discharge lamps present a negative dynamic characteristic that makes necessary using a current limiting element. In high frequency resonant ballasts current limitation is performed by the output resonant tank, but in low-frequency square-wave electronic ballasts arc stabilization is accomplished by stage feeding the square wave inverter. Therefore, the design of the input converter must be made taking into account the lamp dynamic characteristic. This paper presents a new procedure for obtaining the small-signal dynamic characteristic of metal halide lamps is proposed. Using the proposed methodology the small-signal characteristic of a 70 W is obtained, this characteristic is then used for the design of an electronic ballast based on a buck-boost converter followed by a full bridge inverter. The limits for stable operation obtained are verified using a laboratory prototype.