Discharge lamp ballast circuit

摘要

A discharge lamp ballast circuit comprises at least one discharge lamp connected in series circuit with a ballast capacitor and inductor across a pair of input terminals for a source of A.C. supply voltage. A controlled semiconductor switching element is coupled across the lamp electrodes and a control circuit for the switching element is coupled to the input terminals and to a control electrode of the switching element. A voltage dependent non-linear impedance device is connected in shunt with the capacitor so as to limit the capacitor voltage to a predetermined value. The voltage dependent impedance device prevents the occurrence of hazardous voltage levels in the circuit and improves the stability during the warm up phase.