| 摘要 |
PURPOSE:To make small the size of a ring trip circuit and to make circuit integration, by detecting the formation of DC loop due to off-hook of a terminal device with a voltage comparator. CONSTITUTION:A terminal device 1 and a 16Hz oscillator 2 are located outside the electronic ring trip circuit. When the 16Hz AC callout signal from the oscillator 2 is given to a terminal device 1 via a resistor R1, the terminal device 1 in on-hook state produces a callout tone. After the callout signal is rectified at half wave at a diode D2, it gives an ON/OFF signal to a transistor TR6 via an OP amplifier 7. When the terminal device 1 is in off-hook, since the resistance value of the terminal device 1 is lowered to form the DC loop, a voltage of low potential is obtained at the output of OP 4 stably. The logic level detects the off-hook of the terminal device 1 to stop the call-out signal. Thus, the circuit integration and small sized device are obtained. |
