| 摘要 |
PURPOSE:To surely detect a half-wave discharge when the nondischarging voltage of a lamp is relatively low regardless of the discharge direction at the time of a half-wave discharge by detecting the lamp voltage by the AC coupling. CONSTITUTION:A circuit containing resistors R3 and R4 and a diode D2 is connected to a junction, i.e., a node N, between a choke coil L1 and a discharge lamp LP via a capacitor C4. When a half-wave discharge occurs at the life terminal stage of the discharge lamp LP, a wave-form with an asymmetric amplitude is obtained. The nondischarging voltage of the discharge lamp LP is higher than the discharging voltage, the amplitude of the voltage across both ends of the lamp at the time of a half-wave discharge becomes considerably higher than that at the time of the normal operation. When the voltage across both ends of the lamp is detected by the AC coupling, the detected voltage V1 at the time of a half-wave discharge is considerably larger than the detected voltage V1 at the time of the normal operation, the half-wave discharge state can be detected very correctly. |
