| 摘要 |
PROBLEM TO BE SOLVED: To improve the rate of inputs and to simplify a high voltage generating circuit for cost reduction by causing operation of a lighting device at a no-load resonance frequency that is characteristic of a piezoelectric transformer, and directly switching using a converter a pulsating current obtained through rectification of an ac input. SOLUTION: An alternating current inputted to an ac input circuit 1 having a high-frequency noise filter is rectified into a direct current for input to a converter circuit 2. Then the direct current enters an inverter circuit 3 and turns on an HID lamp; at initial stages, a high voltage is produced by a high voltage generating circuit 4 at a no-load resonance frequency which is characteristic of a piezoelectric transformer. A converter driving pulse width control circuit 5C compares an output voltage of the converter circuit 2 with that of a reference voltage generating circuit 5A via an error amplifier circuit 5B and amplifies the voltage differential. A load current detecting circuit 5D detects the load current of the HID lamp, and controls the converter circuit 2 so that the load current remains constant. Therefore, the rate of inputs is improved, and the high voltage generating circuit is simplified to make cost reduction possible. |
