Patent
1984-11-13
1986-09-30
Rubinson, Gene Z.
H04M 100
Patent
active
046148434
ABSTRACT:
Telephone set with key for opening the loop for a predetermined time interval. A monostable triggering circuit includes an MOS transistor connected in series with the transmitter and dialing circuit and a bipolar transistor having a collector directly connected to the grid of the MOS transistor and a base connected to the drain of the MOS transistor through a capacitor and a diode. The capacitor together with a resistor connected in series therewith constitute a timing circuit. The voltage to which the capacitor is charged during the time that the circuit is open is limited by a Zener diode. Actuation of the key opens the MOS transistor thereby leaving the transmitting and dialing circuit disconnected. The transistor switches back to the conductive state when the timing capacitor has reached the voltage determined by the Zener diode. The MOS transistor is a low impedance in series with the transmitting and dialing circuit when conductive but presents a high impedance as its grid. The impedance seen by the line is thus not disturbed. An additional Zener diode and resistor for overvoltage protection is included.
REFERENCES:
patent: 4086440 (1978-04-01), Hurle
patent: 4251693 (1981-02-01), Christiansen
patent: 4313037 (1982-01-01), Shepard
patent: 4390753 (1983-06-01), Janssen
patent: 4492823 (1985-01-01), James et al.
Briody Thomas A.
Eason Leroy
Rubinson Gene Z.
Streeter William J.
U.S. Philips Corporation
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