| 摘要 |
A power supply circuit (100) for use in driving fluorescent lamps (102, 104, 106 ) has a current mode control voltage boost IC (144) which produces a boosted voltage and has a power control input (pin 3) and a frequency control input (pin 4). The lamps are driven by a self oscillating inverter (178, 180, 196, 198) which is powered from the voltage boost IC and which operates at a frequency independent therefrom. In order to dim the lamps a D.C. bias voltage i s applied to the power control input. At the same lime a commensurate D.C. bias voltage is applied to the frequency control i nput so as to provide power factor correction in dependence on the power produced by the voltage boost IC. The circuit thus provi des a substantially constant, optimum power factor at both full and dimmed light levels.
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