| 摘要 |
A pulse-shaping circuit for a telephone set, designed for a telephone system with loop dialling, by means of an electronic contact, tries to emulate the pulse shape produced with an ordinary finger dial. In such a telephone set, a constant voltage circuit is in series with the electronic contact so as to generate from the line current the feed voltage for the electronic circuits which control the dialling. In order to obtain, as with a finger dial, a slow decrease in the line current at the beginning of the cut-out pulse, due to spark extinguishing, and a rapid increase after the end of the cut-out pulse, an energy storage circuit is arranged so that during the cut-out pulses it is connected to a charging current path to the line voltage in series with the control circuit of the dialling transistor and during the turn-on pulses it is connected to a discharge circuit path in series with the control circuit to a short- circuiting transistor, connected across the constant voltage circuit (zener diode). <IMAGE> |
