| 摘要 |
A ballast ( 10 ) for powering at least one gas discharge lamp ( 70 ) having heatable filaments ( 72,74 ) includes an inverter ( 200 ), a resonant output circuit ( 400 ) coupled between inverter ( 200 ) and lamp ( 70 ), and a filament heating and ignition control circuit ( 600 ) coupled to inverter ( 200 ) and resonant output circuit ( 400 ) having a first resonant frequency and a second resonant frequency, wherein the first resonant frequency is substantially greater than the second resonant frequency. Filament heating and ignition control circuit ( 600 ) controls inverter ( 200 ) and resonant output circuit ( 400 ) during a preheat phase and during a normal operating phase. During the preheat phase, resonant output circuit ( 400 ) has an effective resonant capacitance corresponding to the first resonant frequency, and provides a first level of heating to the lamp filaments ( 72,74 ). During the normal operating phase, resonant output circuit ( 400 ) has an effective resonant capacitance corresponding to the second resonant frequency, and provides a second level of heating to the lamp filaments ( 72,74 ) that is negligible in comparison with the first level of heating. Control circuit ( 600 ) monitors a voltage within resonant output circuit ( 400 ) in order to compensate for any variation in the parameters of resonant output circuit ( 400 ) and to ensure that an appropriate level of preheating is provided to lamp filaments ( 72,74 ).
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