| 摘要 |
PURPOSE:To restrict temperature rise in the vicinity of an electrode by reducing a current value to be supplied when it is detected that an emitter applied to a hot cathode is consumed. CONSTITUTION:A switching element S remains 'ON' until a lighting power value by means of a current detection circuit 20 and a voltage detection circuit 21 exceeds a reference power value. In these circuits, when a state of a lamp 10 being lighted in a hot cathode mode starts to change to a state where lighting is carried out in a cold cathode mode with an emitter being consumed, the lighting voltage of the lamp is raised and the lighting power is thus increased. Chopper control is performed by the switching element S so that the lighting current is reduced as much as the cathode drop voltage is raised by a comparison circuit 22. Current to be supplied is reduced for a fluorescent lamp, for which only a hot cathode is used, by detecting the rise in the cathode drop voltage that can occur by the consumption of the emitter. |
