| 摘要 |
PURPOSE: To provide lighting device whose output can be made constant even with a DC voltage where a high-frequency ripple is superposed. CONSTITUTION: A field-effect transistor Q1 is switched by a drive circuit 2, a high-frequency ripple is superposed within a range where no light ripple is generated at a halogen lamp IL, the voltage is smoothed by a capacitor C1 for a constant voltage, and the halogen lamp IL is turned on. An output voltage is detected by a detection coil L2, the voltage is rectified by a diode D2 and is smoothed by a capacitor C2, and the voltage is divided by resistors R1 and R2 and is compared with the voltage of a reference voltage source E1 by an operational amplifier OP1. When the output voltage is low, the field-effect transistor Q1 is controlled in a direction for boosting the voltage of the capacitor C1. When the output voltage is high, the field-effect transistor Q1 is controlled in a direction for reducing the voltage of the capacitor C1. A voltage gain AV of the operational amplifier OP1 is set so that the voltage of the capacitor C1 decreases as the voltage of the DC power supply E increases. |
