| 摘要 |
PURPOSE:To obtain the free voltage input circuit of a wide tolerance by inputting an input voltage to a photo-coupler through a current matching circuit serially connected to a resistor thermally combined to a thermister for the parallel circuit of a positive characteristic thermister and a capacity. CONSTITUTION:When a current is flows to the input side of a photo-coupler 26, a resistor 23 thermally combined to a positive characteristic thermister 22 generates heats, and when an input voltage is increased, since a resistance value is increased so as to compensate the voltage and the current is limited, the tolerance of the input voltage can be obtained quite widely. Since the thermister 22 is thermally combined with a resistor, a satisfactory compensating characteristic is shown, a response until a thermal equilibrium is achieved is is obtained quickly and a photo-coupler is enough protected. Since a parallel capacity 24 supplies a current to the photo-coupler without generating heats in the case of an alternating input voltage, the tolerance of the input voltage comes to be larger than the time of a direct current. Thus, the presence or absence of the signal voltage of the alternating current and direct current of a wide voltage can be detected with a simple circuit constitution.
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