HID LAMP OPERATING CIRCUIT

摘要

An operating circuit which does not malfunction even if a counter-electromotive force is produced because of the inductance of the wiring of when the operating circuit is installed away from the HID lamp and does not flicker even if the interelectrode resistance of the HID lamp is different in the direction of the applied voltage. An ac rectangular waveform voltage is applied to the HID lamp (1) by a full-bridge inverter (9). the forward and reverse resistances of the lamp (1) corresponding to the polarity of the ac rectangular waveform voltage are measured. The duty ratios in the forward and reverse directions of the ac rectangular waveform voltage are so determined as to be in inverse proportion to the magnitude of the resistances, respectively. A control unit (C) for selecting switching elements (12A-12D) of the inverter (9) is provided to control the ac rectangular waveform voltage so that it may have a voltage waveform to maintain the voltage at the earth potential for predetermined time when the polarity of the ac rectangular waveform voltage is inverted.