PURPOSE:To obtain a titled switch withstanding a high voltage and generating no current branch by using a field effect transistor (FET) as a switch element and using a photocoupler having a photo thyristor, whose high voltage widthstanding type is easily attained, as a control element. CONSTITUTION:An FET 10 used as the switch element is connected between terminals 51 and 52. A photocoupler 11 used as the control element consists of a photo thyristor 11A and a light emitting diode 11B. The photo thyristor 11A is connected between a drain terminal D and a gate terminal G of the FET 10, and the light emitting diode 11B is fed from a control power bus 55 through a resistor 56; and when a closing switch 13 is made, a current flows to the light emitting diode 11B to emit light, and the photo thyristor 11A is turned on. A resistor 12 is set to such high resistance value that the current flowing through the resistor 12 is lower than te holding current of the photo thyristor 11A.
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