| 摘要 |
In order to produce an electrical circuit arrangement to prevent the occurrence of loop dial pulses on the line wires of a telephone connection, the circuit arrangement being activated or de-activated by a key-operable switch which can be implemented using all-electronic components, the desired switching function furthermore being achievable purely by means of voltage monitoring, it is proposed to insert between the line wires a circuit in which the switch (S1) is disposed and into which a resistor (R6) acting as a substitute for the telephone set resistor, the drain terminal of a self-locking MOSFET-transistor (T2) and the source terminal of the transistor (T2) are connected in series downstream of the switch, the gate terminal of said transistor being disposed in parallel with the drain-source path, with a capacitor (C3) connected in series upstream so that, when a dial pulse occurs, its rising edges are transferred from the capacitor (C3) to the gate of the transistor (T2), the transistor (T2) is through-connected and the loop current is received by the resistor (R6) during the pulse period. <IMAGE>
|
