| 摘要 |
1. A telephone dialling keybord comprising generating means (8a) assuring either the opening of the line for generating the decimal numbering pulses or the transmission of dual frequency signals to establish the multifrequency dialling mode, a resistor (6) and a transistor (8) connected in series with means of supply (11) for the keyboard and the set, the transistor (8) being controlled by means of a control circuit (5) to produce a limitation of the current passing through the generating means (8a) and the supply means (11), characterized in that : - the control circuit (5) operates the transistor (8) to display a voltage-current characteristic comprising a section (24) of progressive current reduction ; - an overvoltage suppressor component (7) of the Diac type is connected in parallel with the aggregate formed by the transistor (8), the generating means and the supply means (11) ; - the resistor (6) is a fusible resistance and is connected in series with the aggregate formed by the supply means (11), the transistor (8), the generating means (8a) and the overvoltage suppressor component (7). |
