| 摘要 |
PURPOSE:To eliminate the need for a relay disconnecting a line monitor relay from a line according to the start, and to make the circuit small with the electronic circuit, by increasing the input resistance of a line monitor circuit for detection of voltage. CONSTITUTION:At no communication, when a voltage of lines c, d is low, since Vz1>Vz2 is obtained, where Vz1 and Vz2 are voltages of Zener diodes ZD1 and ZD2, an output of an operational amplifier 8 is high. When the voltage of the lines c, d is high, the voltage is clamped with the Zener diodes ZD1, ZD2, and the voltage inputted to (+) terminal of the operational amplifier 8 is high through the relation of voltage of the ZD1, ZD2, and the output of the operational amplifier 8 goes to high level. That is, at no communication, if the lines c, d are failed, the output of the operational amplifier 8 goes to high level at all times, a closing signal is given to an outgoing trunk at the transmission side and the line is forcedly restored. |
