| 摘要 |
PURPOSE:To enable to transmit current polarity inversion pulse and to make small and light the constitution of power supply circuit, by controlling the call current and direction fed to a telephone set through electronic means without electromagnetic relays. CONSTITUTION:The output of a DC power supply E is commutated in a given frequency with a polarity inversion switch SW-C, and a bipolar rectangular wave output with this polarity inversion is fed to a rectifying circuit REC via a reactance circuit Z with a given impedance, the output rectified at the circuit REC is smoothed at a low pass filter F to be fed as call current to a telephone set Tel. The filter G in this circuit consists of transistors TRs 1-4, resistors r1-r4, solidstate inductance including capacitors C1-C4, and capacitor Ci. Phototransistors PT1-PT2 are connected to the post stage of the solidstate inductance so that the call current can be delivered forward or reverse or stopped with external control, allowing to transmit the current polarity inversion pulse. |
