Electronic starter for fluorescent lamps with controlled pre-heating - uses dual timer integrated circuit to control preheating and high voltage generation by switching thyristors

摘要

The starter uses a dual timer integrated circuit to control the pre-heating of the tube filaments and to then initiate the high voltage over the electrodes to ignite the tube. The circuit automatically precludes the operation of the heater while the high voltage is being generated and vice versa. The filament heating is controlled by the timer switching on the first thyristor. While the first thyristor is on the supply to the high voltage circuit is shorted out by this thyristor. At the end of the pre-heat time the timer turns on a transistor to activate a second thyristor in a series inductor-capacitor circuit. The capacitor charges to the supply voltage and the second thyristor turns off giving to lack of current. This allows the gate of a third thyristor to become forward biassed and discharge the capacitor through the saturable inductor generating a voltage spike each time saturation occurs.