| 摘要 |
<p>PURPOSE:To constitute all detecting circuits of the titled circuit into low power circuits and to minimize the scale of the circuit, by insulating a subscriber line from a telephone exchange with a photocoupler and linearly operating the photo coupler. CONSTITUTION:Photo couplers 4 and 10 and current limiting resistors 6 and 12 are connected between primary coils 8 and 13 of a hybrid transformer 7 connected to party line telephone sets 15 and 16 at a subscriber circuit side 1 and the positive side and the negative side of an office battery 3, respectively. Each of transistors 21 and 22 in each of the couplers 4 and 10 is connected to voltage comparators 28 and 30 at the exchange side, respectively. A resistance 23 and a variable resistance 24 which determine the current-voltage conversion gain of the couplers 4 and 10 are connected to the base of each transistor 21 and 22, and resistances 25 and 26 for outputting voltage are connected to the emitter. Then, a reference voltage is added to the comparator 28 and the output voltage of the coupler 4 is compared with the reference voltage, and the outputs of the couplers 4 and 10 are compared with each other at the comparator 10, and thus, it is automatically discriminated which subscriber makes the call or uses the line. Thus the scale of the circuit is minimized.</p> |
