Method and apparatus for a unidirectional switching, current limited cutoff circuit for an electronic ballast

A lamp inverter circuit (A) includes a switching portion that converts a bus voltage signal (11) into an alternating current signal. An input portion receives the bus voltage signal, and a resonant load portion (70,72) drives a lamp. A preheating portion (16) heats the lamp (12) prior to ignition, and thereafter renders itself inactive following ignition of the lamp (12). A method of starting a lamp (12) includes receiving a bus voltage signal, converting the bus voltage signal into an alternating current signal, preheating the lamp (12) to an ignition temperature, igniting the lamp (12) and inactivating the preheating after the lamp has been ignited. A method of igniting an auxiliary lamp (120), including detecting a conductive state of a main lamp (12) in a lamp ballast circuit (10), the detecting being by a switch (94) that controls preheating of the main lamp (12). The integrity of the main lamp (12) is detected, and current flow is switched from the main lamp (12) to an auxiliary lamp (120) in the event