| 摘要 |
PURPOSE:To prevent a filament from its ignition at the time of nonlighting by detecting only an output current reduced at the time of abnormality of lamp nonlighting or the like. CONSTITUTION:At the time of normal lighting, voltage VR5 generated in a resistor R5 obtains an AC component waveform of the voltage detected with positive/negative almost symmetrical. A detection level Vr1 of a comparator CP1 is set to a VR5 peak at the time of normal lighting to provide a setting limit level. This level is decreased low as compare with the conventional detection level Vr1. When an electric discharge lamp 1a is not lighted, since a resonance current flows in a capacitor C2, choke coil L2, transistor Q1 and the capacitor C2, choke coil L2, capacitor C1, a current iR4 flowing in a resistor R4 is increased. Further, a current of positive/negative almost symmetry flows in the resistor R4. Here is performed control so as to obtain a relation where VR5peak = Vr1, but since an iR4peak ( iL peak) is decreased low as compared with the conventional example, a load current is reduced from the conventional example. |
