| 摘要 |
In an electronic ballast, a half-bridge inverter is powered from a DC voltage and provides a 40 kHz squarewave inverter output voltage. The DC voltage is obtained via a pre-converter with a control input operative to permit control of the magnitude of the DC voltage. The 40 kHz squarewave inverter output voltage is applied across a series-resonant L-C circuit, thereby establishing a 40 kHz sinusoidal voltage across the L-C circuit's tank capacitor. By controlling the symmetry of the squarewave voltage, the magnitude of the 40 kHz sinusoidal voltage is regulated to be appropriate to instant-starting a gas discharge lamp. Each of several instant-start fluorescent lamps is series-connected with a capacitor, such as to form several lamp-capacitor series-combinations, each of which is connected across the tank capacitor, thereby to be properly ignited and powered from the magnitude-controlled 40 kHz sinusoidal voltage. To attain imroved efficiency of operation, after the lamps have all ignited, the magnitude of the 40 kHz sinusoidal voltage is reduced, thereby minimizing the amount of reactive power having to be handled by the various reactive circuit components.
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