| 摘要 |
PURPOSE:To elongate the life of a light emitting device, by a method wherein a plurality of light emitting devices, employed for the ignition of a switching circuit in which a plurality of photo-thyristors are connected in parallel, are provided selectively with gate signals in accordance with load current. CONSTITUTION:A controller for a photo-thyristor is constituted of a gate signal generating circuit A, a light emission control circuit B and a light emission circuit C. A plurality of photo thyristors 3a-3c are connected in parallel to respective arms D in the bridge circuit of a rectifier E while the photo-thyristors are conducted or intercepted by a light gate signal S3 supplied from said light emission circuit C through a light guide 4. In this case, the photo-thyristors 3a-3c are provided in parallel with gate signals sequentially for only a given period of time normally without providing them at all times. When load current increases and exceeds a set value, all of the light emitting devices are provided with the gate signals to put all of the devices ON. When the load current is reduced' a circuit is switched so as to provide said devices with the gate signal sequentially one by one.
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