Patent ID: 6188764
Filing Date: 2001-02-13
Classification: H04M

Abstract:
Protection circuitry for use in a telephone appliance having line interface circuitry adapted to be coupled to a telephone line and ring-detection circuitry, the protection circuitry comprising:a switch, connected between the interface circuitry and the telephone line, the switch selectively having an open state and a closed state wherein the line interface circuitry is coupled to the telephone line;detection circuitry comprising a pair of diodes and portions of the ring-detection circuitry, connected to the telephone line in parallel with the line interface circuitry, to detect an over-voltage condition on the telephone line when the switch is closed, the diodes having a breakdown voltage above which current may flow through the diodes in a reverse direction, the diodes disposed with opposing directions of forward current flow at voltage levels below the breakdown voltage, the portions of the ring-detection circuitry generating a signal indicative of the over-voltage condition when the switch is closed and the voltage on the telephone line exceeds a predetermined voltage level determined by the breakdown voltage of the pair of diodes, wherein the ring-detection circuitry and the detection circuitry share a signal line connecting the ring-detection circuitry and the detection circuitry to the controller; anda controller coupled to the detection circuitry and the switch, the controller responsive to the signal causing the switch to assume the open state.