Voltage-comparator, solid-state, current-switch starter for fluorescent

Abstract

A starter for a fluorescent lamp selectively conducts current from an AC power source through a ballast and cathodes of the lamp during one half cycle of conducted current from the AC power source. Thereafter and during the same on half cycle of current the starter ceases conducting current substantially instantaneously when the current is of a predetermined level. The resulting di/dt generates a starting voltage pulse from the ballast sufficient to ignite the plasma. The starting pulse occurs when the AC voltage across the cathodes exceeds an ignition voltage of the plasma. Preferably the starter employs a thyristor which has a predetermined holding current at least equal to the predetermined level to allow the inherent commutation of the thyristor to create the di/dt. The current conducted by the thyristor heats the cathodes prior to igniting the plasma. A voltage sensing capability associated with the starter triggers the thyristor into conduction only when the voltage across the cathodes exceeds the ignition voltage of the plasma, which occurs when the fluorescent lamp is not lighted, and therefore automatically starts the lamp. Lamp dimming and programmable turn on and turn off conditions are easily effected by timing an ignition and extinguishing sequence.