Patent ID: 7312588

Claim:
A ballast for powering at least one gas discharge lamp, the ballast comprising: an inverter having a load-dependent operating frequency; an output circuit coupled to the inverter, the output circuit comprising output connections adapted for coupling to a lamp load comprising at least one gas discharge lamp; and a lamp fault protection circuit coupled to the inverter, wherein the lamp fault protection circuit is operable: (a) to monitor a fundamental frequency of an electrical signal within the inverter for indication of a lamp fault condition, wherein a lamp fault condition is deemed to have occurred when the fundamental frequency of the electrical signal exhibits a change that exceeds a predetermined change threshold; (b) to provide a starting period wherein the inverter is enabled and allowed to attempt to start the lamp, independent of occurrence of a lamp fault condition; (c) in response to occurrence of a lamp fault condition after completion of the starting period: (i) to disable the inverter and to keep the inverter disabled for a shutdown period; and (ii) after completion of the shutdown period, to again provide the starting period whereby the inverter is enabled and allowed to attempt to start the lamp, independent of occurrence of a lamp fault condition.