| 摘要 |
PROBLEM TO BE SOLVED: To provide a current detector for a communication line which is small in size and low in cost without being affected by other parts. SOLUTION: The current detector for the communication line is provided with: a detection resistor R1 placed in series with a communication line; a DC voltage detection circuit 2 for detecting a DC voltage across the resistor R1; first and second comparators 3, 4 for discriminating whether the DC voltage is higher than a voltage Vr1 or lower than a voltage Vr2; a DC current photocoupler drive circuit 5 for driving a DC current photocoupler circuit 6 when the DC voltage is higher than the voltage Vr1 or lower than the voltage Vr2; an AC current detection circuit 7 for detecting an AC current flowing through the detection resistor R1 on the basis of the DC voltage across the detection resistor R1; and an AC current photocoupler drive circuit for driving an AC current photocoupler circuit 8 on the basis of the detected AC current. COPYRIGHT: (C)2003,JPO
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