| 摘要 |
A lighting system is provided having a central power supply which includes an AC to DC converter. The DC power is distributed to a plurality of ballast circuits for discharge lamps. Each ballast circuit includes an inverter circuit for inverting the DC power to AC power of sufficient voltage to operate the associated lamps. Should the AC input power for the central power supply fail, batteries may be provided to supply the DC power continuously without interruption. The inverter circuits are operated at high frequency to reduce audible noise and eliminate noticeable strobing. The inverter circuit includes a switching circuit controlled by a pulse train. The duty cycle of the pulse train is controlled in accordance with a composite feedback signal which is the product of signals representative of the lamp operating voltage and lamp current.
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