Gas discharge lamp ballast circuit with electronic starter

Abstract

A ballast circuit with an electronic starter for a gas discharge lamp having a pair of cathodes is disclosed. The circuit comprises a main current path with a first leg connected to one cathode of the lamp and a second leg connected to the other cathode. The first leg includes an inductor. A starting current path is connected between the cathodes for enabling current build-up in the inductor during a lamp pre-start period. The starting current path includes a starter switch controllable by the voltage between a control node and a reference node of the switch. The starting current path allows cathode-to-cathode current flow when the starter switch is on. A control circuit is connected between the control node and the reference node of the switch for controlling the switch. The control circuit comprises a capacitor whose voltage is coupled between the control node and the reference node so as to control the switch, and a source of current for charging the capacitor. The control circuit further comprises a voltage-breakover (VBO) switch coupled to receive the voltage of the capacitor in order to be made conductive when that voltage reaches a sufficient level. The VBO switch is coupled between the reference node and the control node in a manner that maintains the voltage between those nodes at a sufficiently low level to keep the starter switch turned off after such switch is made conductive.

Dependencies are inferred from the claim text.