| 摘要 |
Disclosed is a ballast circuit for a gas discharge lamp, including a resonant load circuit with a gas discharge lamp and first and second resonant impedances whose values determine the operating frequency of the resonant load circuit. The ballast circuit further includes a d.c.-to-a.c. converter circuit coupled to the resonant load circuit so as to induce an a.c. current in the resonant load circuit. The converter circuit comprises first and second switches serially connected between a bus conductor at a d.c. voltage and ground, and has a common node through which the bidirectional load current flows. A feedback arrangement regeneratively controls the first and second switches, and includes a circuit for sensing a.c. current in the resonant load circuit and producing a feedback signal in proportion to the a.c. current. The feedback arrangement includes a comparator circuit for comparing the feedback signal with a periodic reference signal, and for producing a comparator output signal that changes state when a first one of the compared signals becomes greater than the second of the compared signals, and that further changes state when the second of the compared signals then becomes greater than the first of the compared signals. Further included in the feedback arrangement is a circuit for generating the periodic reference signal in response to the comparator output signal, and a conditioning circuit receptive of the comparator output signal for controlling the first and second switches.
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