Importance

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Abstract

A ballast circuit for energizing a lamp includes an inverter circuit having a switching element with a conduction state controlled by a control circuit which limits a voltage applied to the lamp. In one embodiment, the control circuit includes an integrated circuit providing a conduction control signal to a duty cycle control circuit. The conduction control signal alternately biases the switching element to conductive and non-conductive states at a first duty cycle when the lamp voltage is below a predetermined level. When the lamp voltage becomes greater than the predetermined level, the duty cycle control circuit decreases the switching element to a second duty cycle, which is less than the first duty cycle, to reduce the voltage at the lamp. In one embodiment, the ballast regulates the lamp current to a predetermined level such that the ballast can energize a lamp which can vary in length and has a predetermined diameter. In another embodiment, the integrated circuit provides the conduction control signal to a plurality of duty cycle control circuits forming a portion of further inverters for independently energizing multiple lamps. In a further embodiment, a modular ballast for energizing a plurality of lamps includes a plurality of replaceable modules.

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First Claim