Patent ID: 6222322
Filing Date: 2001-04-24
Classification: H05B

Abstract:
A ballast circuit comprising:an output circuit for producing a lamp drive current used for driving an electric discharge lamp; anda ballast protection circuit for protecting the output circuit from excessive lamp drive current, comprising:a current sensing resistor for producing across it a current sense voltage that varies as a function of the lamp drive current, anda device responsive to said current sense voltage for preventing said output circuit from producing said lamp drive current when said current sense voltage reaches a predetermined voltage range indicative of excessive lamp drive current wherein said voltage-responsive device includes a device having a controllable conduction path responsive to said current sense voltage, said controllable conduction path coupled to the gate and source of a first effect transistor for shunting said gate and source of said transistor when said current sense voltage is within said pre-determined voltage range, thereby causing said inverter from generating said oscillating lamp drive current; andwherein said output circuit includes said inverter comprising said first field effect transistor and a second field effect transistor in a push-pull configuration including a feedback device for causing said inverter to generate an oscillating lamp drive current.