| 摘要 |
PURPOSE:To prevent malfunction and burning of an operation coil by providing serially connected bias resistor, a light emitting diode of photocoupler and a nonlinear element which shows a low impedance at a voltage higher than the limited voltage between the DC output terminals of full-wave rectifier. CONSTITUTION:A Zener diode 14 is connected in series to a light emitting diode 10 of photocoupler 8. A Zener voltage of the Zener diode 14 is selected so that it is lower than a DC voltage applied to the Zener diode 14 corresponding to total voltage of AC voltage to be input to a full-wave rectifier 1 through a changeover switch 3 and is higher than a DC voltage applied to the Zener diode 14 corresponding to an AC voltage branched through a capacitor 4 and a resistor 5. Thereby, a current is caused to flow into a light emitting diode while the movable iron core is attracted and the current flowing in to the light emitting diode can be perfectly cut off while the iron core is held, thus forming a series circuit of operation coils 2a and 2b reliably. Moreover malfunction and reduction of holding current can be reduced and burning and deterioration of insulation property of coil 2b can be also be prevented.
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