| 摘要 |
PURPOSE:To use a ring trip circuit with no adjustment over a wide range by detecting only a potential difference at both ends of a resistor for detection in the ring trip circuit used for a subscriber line interface section of an exchange. CONSTITUTION:When a called party hooks on, a DC closed loop is formed, a DC current starts flowing, and a voltage drop produced in a sensing resistor 5 due to this DC current appears as potential difference VE-VF, but since the current is DC in this case, the current is not attenuated by a low pass filter. Thus, a value of coefficient (a) is to be given so as to flow a sufficient current to a light emitting diode of a photocoupler 24. Thus, a photodetecting transistor is turned on, the output goes to a ground potential, thereby allowing the ring trip circuit detecting only the DC current to be constituted. |
