Electronic ballast with pulse detection circuit for lamp end of life and output short protection

摘要

An electronic ballast for fluorescent lighting includes an inverter circuit having an output circuit coupled to a pair of lamp terminals. A protection circuit is coupled to one of the lamp terminals. The protection circuit includes a differential voltage sensing circuit that is functional to sense the lamp voltage pulses as sudden changes in voltage across a DC blocking capacitor and, in response, to provide a positive AC voltage pulse. A pulse accumulation circuit is coupled to the differential voltage sensing circuit. The pulse accumulation circuit is responsive to the positive AC voltage pulses from the differential voltage sensing circuit to accumulate the positive AC voltage pulses into the ballast shutdown signal.