Ballast for a discharge lamp with false deactivation detection

Abstract

A ballast for a discharge lamp capable of reliably and successfully detecting the end of the lamp life and ceasing the ballast immediately upon detection of the lamp's life end. The ballast includes a power supply providing from a power source a variable power to the lamp, and a power controller controlling the power supply to apply a high voltage for igniting the lamp and subsequently apply a predetermined power for operating the lamp. A lamp life detector is included in the ballast to detect whether or not the lamp comes to a lamp's life end. Also included in the ballast is a supervisor which issues, upon detection of the lamp's life end, a disable signal prohibiting the power supply from lighting the discharge lamp. The power controller provides a detection period of a limited short time period starting from energization of the ballast such that the lamp life detector can detect the lamp's life end and issue a lamp's life end signal only when there is an extinction of lamp within the detection period, and that the supervisor issues, after the elapse of the detection period, an enable signal permitting the power supply to ignite the discharge lamp if the lamp is extinguished after the elapse of the detection period.