| 摘要 |
PURPOSE: To enhance safety, restrain a power loss for reducing unnecessary power consumption, and prevent the deterioration of each circuit section by reducing the occurrence of excessive high voltage at a secondary output side, upon the occurrence of such an event as the discontinuity of a discharge tube filament and the supply of power without mounting a discharge tube. CONSTITUTION: Regarding a lighting circuit used for a separately excited inverter type discharge lamp turned on after discharge tubes 8 and 8' are preheated with high-frequency AC power obtained from the switching operation of an exciting circuit 4 capable of outputting a variable oscillation frequency, an excited frequency control means 5 is provided for gradually raising and holding the output frequency (f) of the circuit 4 from the preset frequency f2 determined at the time of starting power supply, toward the higher preset frequency f3. In this case, a preheating current limiting means 6 may be added for limiting the preheating current of the circuit 4 and setting the secondary output voltage thereof at a lower level, when the preheating current is equal to or less than the preset value. |
