Electric lamp and discharge devices: systems – Periodic switch in the supply circuit – Silicon controlled rectifier ignition
Patent
1993-06-11
1997-03-04
Pascal, Robert
Electric lamp and discharge devices: systems
Periodic switch in the supply circuit
Silicon controlled rectifier ignition
315309, 315DIG7, 307326, H05B 3700
Patent
active
056082916
ABSTRACT:
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-second. 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.
REFERENCES:
patent: 3889153 (1975-06-01), Pierce
Pascal Robert
Shingleton Michael
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