| 摘要 |
PURPOSE:To eliminate the need for the application of power supply to a detection circuit at all times, by charging an incoming signal to a capacitor in the incoming state, discharging the charge and obtaining an output of incoming response and detection. CONSTITUTION:When a calling signal is applied to connection terminals 1a, 1b, a capacitor 7-4 is charged via a diode bridge 7-1. In closing hook switches 2a, 2b to the call signal, a DC loop is closed via a channel circuit 3 and power is applied to an incoming call response and detection circuit 7 with the operation of a switch 2b. When a power supply voltage is applied, a pulse generating circuit 7-13 is operated and a transistor (TR) 7-12 is set on. Thus, a current flows to a photo diode of a photocoupler 7-8 and its photo TR is set on. Thus, the charge in the capacitor 7-4 is discharged via the photo diode of a photocoupler 7-7 and an incoming call response-and-detection output is obtained through a wave forming circuit 7-14. |
