| 摘要 |
PURPOSE:To attain the increase in the operating margin through circuit insulation and to reduce the effect on other circuits, by insulating the intput and output of a ring trip. CONSTITUTION:In applying an AC current between terminals 1 and 2, the current is by-passed through a capacitor C1 and no AC voltage is generated between the terminals 1 and 2. Thus, no current flows to a diode of a photocoupler PC1, and a transistor of the coupler turns off. A Zener diode RC1 is provided to prevent malfunction in detection of subscriber ring AC current due to the AC current component which can not be by-passed with the capacitor C1 for the subscriber ring AC current when the subscriber is called and the subscriber is at on-hook. Simultaneously, the RC1 determines the threshold value of the detection current of a DC current between the terminals 1 and 2. Thus, the malfunction due to the leakage current of subscriber relay line and telephone set circuit can be prevented. |
