Hybrid electronic ballast operating the HPS lamp at constant power

A hybrid solid-state ballast that operates high-pressure sodium (HPS) lamps at main frequency with constant power through rated life is described. The system utilizes two inductors connected in series and a bidirectional semiconductor switch connected in parallel to one of them. A lamp starting circuit has also been included in the ballast. The static switch, with phase angle control provided by power feedback, actuates on lamp current, compensating variations of the main voltage and increases of lamp arc voltage. The system offers the following: (1) an increase of lamp life and system lumen maintenance; (2) power factor and total harmonic distortion of line current comparable to conventional lag ballast; and (3) operating cost savings, both in terms of energy cost and lamp replacement cost