| 摘要 |
PURPOSE:To simplify the constitution of the line circuit through actuation of the relay driving circuit after securing the AND between the ringing tone control signal and the output of the hook information detecting circuit. CONSTITUTION:When the telephone is hooked off for calling, the DC current flows in the route of power source E-resistance R1-line L2-the telephone-line L2-resistance R2-R3-power source E. In this instant, transistor TR conducts with the voltage produced across resistance R3, and thus diode D conducts. Thus output terminal T0 features the L level. On the contrary, the H level is applied to ringing tone control input terminal T1 at the called time, and thus AND gate G2 opens to give actuation to relay K. Accordingly, the connection is secured between capacitor C0 and ringing tone signal source V. In such way, the ringing tone is transmitted to the telephone. At this moment, the voltage caused across resistance R3 is applied to TR via resistance R4 and capacitor C0. And thus TR does not conduct. Accordingly, terminal T0 is kept at the H level, and relay K keeps the actuating state each. Here if the telephone gives the answer, the TR conducts. As a result, terminal T0 features the L level with relay K released, thus carrying out the ring trip. |
