Preheating and starting circuit and method for a fluorescent lamp

摘要

The cathodes of a fluorescent lamp are preheating and the medium between the cathodes is ignited into a plasma by heating the cathodes for a predetermined warm-up time period by conducting current from a supply power source through the cathodes for a conductive time interval, and applying a relatively high voltage starting pulse to the cathodes at the end of the conductive time interval or alternatively suppressing the high voltage starting pulse during the predetermined warm-up time period. Suppressing the high voltage starting pulse during the warm-up time period, thereby preventing erosion the thermionic coating of the cathodes due to positive ion bombardment. A controllable semiconductor switch is connected to the cathodes to control the current flow through them. The high voltage starting pulse is derived from commutating the semiconductor switch into a nonconductive state when the applied current level drops to the characteristic holding current value of the switch. The high voltage starting pulse is suppressed by triggering the semiconductor switch at the time when it would otherwise be commutating to the nonconductive state.