| 摘要 |
<p>PURPOSE:To increase a response detecting margin by providing a switch circuit short-circuiting an inductance circuit of a feeding circuit to detect stably a calling signal at a subscriber terminal. CONSTITUTION:At the transmission of a ringing a bell of a telephone set TEL is rung by a path of ground, ring signal source CR, resistor R1, switch S1, telephone set TEL, switch S6, switch S7, feeding resistor R3 and battery at the positive half cycle period; and a path of battery, resistor R2, switch S2, telephone set TEL, switch S1, resistor R1, ring signal source CR, and ground at the negative half cycle. The detection of response is attained by a detecting circuit TRIP. Since inductances L1, L2 of the feeding circuit are short-circuited by the switches S7, S8 during the transmission of a ringing, the adverse effect of inductance is avoided. The delay in the leading of a current waveform by the inductance L1 when the signal is changed over from the negative to the positive half cycle is prevented, allowing to prevent the reduction of detecting margin of the TRIP circuit.</p> |
