POWER CONTROL CIRCUITRY FOR SUBSCRIBER CARRIER TELEPHONE SYSTEMS

摘要

The control circuit comprises: a first transistor, a delay circuit, and a voltage divider that are connected in series between a supply voltage and a reference voltage; and a second transistor that is responsive to the voltage on the divider and conduction of the first transistor for conducting to energize a loop relay. The delay circuit comprises the parallel combination of a resistor and capacitor that are connected in series with the first transistor and divider, and are connected across the base-emitter junction of a third transistor. The integrator averages output current of the first transistor for turning on the third transistor to connect the supply voltage therethrough to a carrier oscillator only in response to input signals to the first transistor that have a duration greater than a prescribed value that is set by the integrator. The output of the third transistor is coupled to the oscillator through a decoupling diode that prevents conduction in the reverse direction through the collector-base junction of the former which may then deenergize the relay and open the central office loop.