JPS5460775A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To provide the subject device wherein lamp current, light output of lamp and lamp power are detected, and a semiconductor switching element controlling the AC source voltage in response to the output signal is phase-controlled, thereby preventing the flickering of the lamp. CONSTITUTION:A predetermined voltage is applied to a capacitor 118 by a constant-voltage diode 116. A lamp current flowing to a discharge lamp 111 is detected by a detection circuit 110, and applied to the gate electrode G of a programmable unijuncetion transistor PUT. When the potential of the anode A of the transistor PUT becomes equal to that of the gate G, the transitor PUT becomes conductive, and the capacitor 118 discharges to generate a pulse voltage at the secondary winding of a pulse transformer 120, said pulse voltage being applied to the trigger electrode of a semiconductor element 113 to phase-control the same. By such procedure, lamp currents of both positive and negative cycles of the source voltage are made equal to each other to prevent the occurrence of flickers.