Solid state four-wire switch for key telephones
OwnerJohn W. Ervininventor
Life of this patent
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Abstract
A compact, solid state four-wire switch for use with key telephones. The switch comprises a pair of transistors which, in the two-wire mode, electrically connect a telephone receiver with a telephone circuit balance network. In the four-wire mode a negative potential derived from the four-wire station pickup relay turns off the switch by reverse biasing the switch transistors to thereby electrically isolate the receiver from the balance network. The transistors are encapsulated within a thin, generally rectangular housing module which is adapted to be mounted interiorly of a key telephone on any of the pre-punched mounting holes therein. Electrical connection with the telephone circuitry is facilitated by three screw down terminals mounted on the module and three module leads equipped with terminal connectors.
Claims8
A solid state switch for switching between a two-wire operating mode and a four-wire operating mode in a telephone, said telephone including a two-wire circuit comprising a pair of conductor lines connected with a telephone balance network for operation in the two-wire mode and a four-wire circuit having a pair of receiver lines bypassing the balance network for operation in the four-wire mode, the switch comprising:
- first and second network lines adapted to be electrically connected to the telephone balance network;
- first and second receiver terminals adapted to be electrically connected to a telephone receiver;
- solid state switching means for electrically connecting said first network line to said first receiver terminal and said second network line to said second receiver terminal in the two-wire mode, said switching means having means for electrically coupling said first and second receiver terminals with the respective four-wire receiver lines, said switching means comprising a pair of transistors each having base, emitter, and collector electrodes, said base electrodes resistively coupled to ground, said emitter electrodes connected to the respective network lines, and said collector electrodes connected to the respective receiver terminals;
- and
- reverse biasing means for turning off said switching means in a four-wire mode to thereby electrically isolate said network lines from said receiver terminals while electrically coupling said four-wire receiver lines with said receiver terminals.
Dependencies are inferred from the claim text.