Discharge lamp with starter circuit

Abstract

A starter circuit for a hot cathode discharge lamp which has a switching element which is connected across the lamp to permit a cathode heating current to flow and then opens to permit the lamp to strike. The starter circuit has a thyristor as the switch element, and a control circuit for rendering the thyristor conductive at a desired point during each cycle of the applied voltage. The control circuit includes means for increasing the instantaneous applied voltage which is required to trigger the thyristor with successive cycles of the applied voltage after switch-on of the circuit. This means preferably includes a capacitor which is progressively charged to provide an increasing bias which must be overcome by the applied voltage. If the lamp fails to strike, the required voltage for triggering goes on increasing until it is too high for the thyristor to trigger at all. No damage can then occur to the starter circuit or the lamp ballast.

Dependencies are inferred from the claim text.