Abstract: A pulse shaping circuit, for use with two-wire telephone station sets, such as normally associated with electronic private automatic branch exchange systems. The function of the pulse circuit is to regenerate hook-switch and hold-button control signal pulses for transmission to the common switching equipment as finite loop current interruptions of predetermined pulse width. The circuit overcomes false signalling and signal recognition problems caused by loop-current transient interruptions, and by imprecise manual operation of the station hook-switch and hold-button by station users.

Abstract: A novel circuit and method are described for monitoring a telephone line of a switched telephone system. The line monitoring circuit is interposed in the telephone system between the local subscriber-line from the central office and the on-premise continuation of that line at the subscriber's location. The line monitoring circuit has component circuitry for sensing both line-to-ground faults and extraneous AC voltages of a predetermined magnitude and frequency. Upon sensing a line-to-ground fault or an extraneous AC voltage of the predetermined magnitude and frequency, a control signal is transmitted to a relay control element which operates to disconnect the on-premise portion of the line from the portion of the line which extends from the subscriber's premise to the central office of the utility company. Visual indicators are also provided with the circuit. The indicators show whether a line-to-ground fault or an extraneous AC voltage fault has caused the relay to operate.

Abstract: An energy limiting foldback circuit for use with power supply having a power control device in its output. The energy limiting foldback circuit contains a voltage sensing device for sensing the potential drop between the input and the output of the power control device. The foldback circuit also includes a current sensing device for sensing the current through the power control device. A conduction control circuit is included which is responsive to the outputs of the voltage sensing device and the current sensing device. The conduction control circuit acts to control the operating conduction through the power control device. The energy limiting circuit can also include a pulsing circuit operative in the event of output fault to periodically pulse the power control device into a momentary conduction state.