Patent ID: 6781326
Filing Date: 2004-08-24
Classification: H05B

Abstract:
A ballast circuit comprising:a DC input circuit having a high voltage line and a base line; a lamp drive circuit coupled between the high voltage line and the base line; an output circuit coupled to the lamp drive circuit for producing a lamp drive current used for driving an electric discharge lamp, the output circuit includes an inverter comprising first and second field effect transistors in a push-pull configuration including a feedback device for causing the inverter to generate an oscillating lamp drive current; and a ballast protection circuit for protecting the lamp drive circuit, comprising: a detection circuit coupled between the high voltage line and the base line configured to detect when a voltage on the high voltage line exceeds a threshold, and a shutoff device coupled to the detection circuit and to the lamp drive circuit for preventing the lamp drive circuit from producing the lamp drive current when the detected voltage on the high voltage line exceeds the threshold.