| 摘要 |
In a fluorescent lamp ballast, a source of high-frequency voltage is applied directly across a series-resonant L-C circuit. The fluorescent lamp is connected in parallel with the capacitor of the L-C circuit and a voltage-limiting means is operative to prevent the series-resonant L-C circuit from overloading the voltage source during any period when the lamp is not effective in providing circuit loading. When power is initially applied to the series-resonant L-C circuit, a control means provides a short circuit across the capacitor; and, by way of a first current transformer, the resulting short circuit current is used for pre-heating the fluorescent lamp cathodes. After about 1.5 second, the control means provides for removal of the short circuit for a period of about 25 milli-seconds, thereby permitting the voltage across the capacitor to grow to a magnitude sufficient to ignite and operate the lamp. If the lamp ignites, the resulting lamp current is then used, by way of a second current transformer, to prevent the control means from re-providing the short circuit. If lamp current does not flow, or if it at any time ceases to flow, the control means will re-provide the short circuit within about 25 milli-seconds. Thereafter, until power is removed or until an operable lamp is connected, the control means will continuously repeat the cycle of 1.5 second short circuit and 25 milli-seconds open circuit.
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