| 摘要 |
PURPOSE:To obtain an insulated level detection circuit capable of detecting the level of small input quantity of electricity. CONSTITUTION:Provided to an insulated level detection circuit are direct current input terminals 1, 2, a series circuit consisting of a resistor VR1 and such voltage lowering elements as diodes D1, D2 which are connected to the direct current input terminals 1, 2, a series circuit having a Zener diode ZD1 and a resistor R1 connected to both ends of the resistor and a photocoupler PC1 connected to both ends of the voltage lowering element. The constitution attains to distribute the current flowing in the voltage lowering element to the primary side of the photocoupler PC1 when the voltage between the both ends of the resistor VR1 exceeds a certain voltage based on the Zener voltage of the Zener diode ZD1 and obtain output signal by sending current in the secondary side of the photocoupler PC1 so that the level detection of surveillance current itself is possible by using the current quantity of electricity for indication line surveillance which is flowing in the indication line. Furthermore, an insulated level detection circuit LD which does not require an insulated DC power source and is small size and low load, can be obtained. |
