| 摘要 |
PURPOSE:To improve the reliability of a line test deciding circuit by deciding line test of a 48V system irrespective of inside resistance condition of a station. CONSTITUTION:An input terminal 11 is connected to a telephone circuit, and normally and at testing a subscriber's line, a rectifier 12 is inverted in bias and does not work, and at the time of subscriber testing, it works and voltage is supplied to the circuit. In case where a high resistance is inserted owing to the inside resistance condition of the station, the voltage drop of the line becomes larger, and therefore, the voltage generated in a deciding voltage generating circuit 13 becomes smaller and decided as a line test. When low resistance is inserted by inside resistance condition of the station, the voltage generated in the circuit 13 becomes higher, and accordingly, decision is not made by a voltage judging circuit 15, and the presence of a call signal is decided by a call signal detecting circuit 18. Only when there is no call signal, a switching circuit 14 is made off, and power supply of the circuit is cut off.
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