| 摘要 |
PURPOSE:To precisely detect the presence or absence of a feed current by using a comparator having a reference voltage in an internal part when remote feeding is executed to a digital subscriber terminal through a customer interface device. CONSTITUTION:The circuit consists of R10, R21 and R22 which branch a current flowing in a subscriber line and branch a voltage drop by the branched current as resistances R, and the comparator CO 31 to which a power voltage is supplied from the subscriber line through a resistance R30, which has the reference voltage in the internal part and which sets the voltage drop which occur in both ends of R22 to be an input voltage as a detection means 30. The comparator 31 has the reference voltage in the internal part, and it compares the reference voltage with the input voltage. When the input voltage exceeds the reference voltage, an output is generated from the comparator 31. A photo coupler PI is driven by the output voltage of the comparator 31, and the output is generated in the transistor of the photo coupler PI, whereby that feeding is executed in the subscriber line is detected. |
