Design and performance of an electronic ballast for high-pressure sodium (HPS) lamps

An electronic ballast for high-pressure sodium (HPS) lamps was designed and evaluated, theoretically and experimentally. The ballast is based on the half-bridge topology and includes a high-voltage ignitor and dimming capability. It was used to drive and examine the high-frequency characteristics of a commercial HPS lamp (NAV-T 150W (SON-T), OSRAM). The experimental results reveal that, for the frequency range of this study (27-75 kHz), the lamp is free of the acoustic resonance problem. It it as also found that, for the present experimental conditions, the lamp is purely resistive, and the resistance is practically independent of the power level and operating frequency. The lamp exhibited stable operation over a very large dimming range, down to about 7% of nominal power. The 2.8-kV ignition pulse was found to be sufficient for both cold and hot startup under the proposed operating conditions.