| 摘要 |
PURPOSE:To make it possible to automatically control the current amount of a constant current circuit which is manually controlled by a convensional method at the time of using the constant current circuit as a load circuit connected to the transmission line (TIP and RING lines) side of a subscriber's circuit in a digital electronic exchange. CONSTITUTION:The constant current circuit is constituted of an amplifier 1-1 for amplifying a voltage drop due to a loop current flowing into the subscriber's circuit 2 and a voltage subtracting amplifier 1-2 for receiving the voltage drop due to the loop current from the amplifier 1-1 as a feedback voltage, receiving a prescribed voltage also and outputting a control signal based upon difference information between the prescribed voltage and the feedback voltage to a control element 1-4 allowing a fixed loop current to flow into the subscriber's circuit 2. |
