Novel constant power control of electronic ballast for HPS lamps

A ballast that operates high-pressure sodium (HPS) lamps at constant power through rated life is described. It provides nearly constant effective current during the run-up period of the lamp and nearly constant effective lamp power between the minimum and maximum lamp voltage. An ignitor is presented which is sufficient for starting HPS lamps. Based on the analysis of its operation principle, a prototype for 250W HPS lamps is successfully developed. The experimental results show the ballast has a good control characteristic.