| 摘要 |
PROBLEM TO BE SOLVED: To provide an overvoltage protection device and a circuit that respectively have no change in capacitance. SOLUTION: A low-capacitance overvoltage protection circuit 80 provides protection to each communication line 12, 14. A diode bridge 46 is connected to each communication line 12, 14 so that overvoltages of both polarities pass through the overvoltage protection device 44 in one direction. A bias voltage source 48 applies a bias voltage to the semiconductor overvoltage protection device 44 through insulation resistors 64, 66 in order to make the capacitance of the overvoltage protection device 44 independent of changes in communication line voltages. When line voltages exceed the magnitude of the bias voltage, each blocking diodes 82a, 82b prevent a current from flowing through the bias voltage source 48 in a reverse direction. COPYRIGHT: (C)2008,JPO&INPIT
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