| 摘要 |
PURPOSE:To detect the ignition by a protective function by a method wherein an overvoltage-protective function part is separated from a photodetecting part and only an electric current flowing during an operation of the protective function partly flows being branched to a detection element. CONSTITUTION:During a normal ignition operation, the light from an optical fiber 23 is incident on a recessed photodetecting part 8 and ignites a main thyristor 16 via amplification gate electrodes 6, 6' (auxiliary thyristors 14, 15). When an overvoltage is impressed between an anode electrode 5 and a cathode electrode 7, an electric field is concentrated locally in a recessed part 9 and a breakdown electric current is generated. This electric current escapes to a metal electrode 10 along the recessed part 9; (a protective function part 17 is ignited); the current as a gate electric current flows to the amplification gate electrode 6 via a resistor 11, and ignites the main thyristor 16. If the electric current flowing in the protective function part 17 partly flows being branched to an LED 22, the ignition of the protective function part 17 can be detected. As a result, because it is possible to judge whether the ignition by the light is defective or not, the reliability can be enhanced. |
