Subscriber drop circuit for controlling drop current with load and maximizing power usage

摘要

A circuit for supplying drop current to the subscriber connected to the remote terminal of a central office powered telecommunications system. A switching regulator is included in the circuit for generating the drop current. The switching regulator adjusts its conduction time as a function of the length of the loop connecting the subscriber to the terminal such that the subscriber consumes only that power required by the loop length. The switching regulator operates in response to a reference current generated by a control circuit. A central office supplied signal on the transmission means connecting the central office to the terminal is used for transferring power to the terminal. The amplitude of that signal at the terminal varies with system load. When that amplitude deviates in a predetermined direction from a reference signal of predetermined amplitude the reference current and therefore the drop current to all off hook subscribers is uniformly decreased by an amount which allows the power transferring signal amplitude to be maintained substantially equal to the amplitude of the reference signal.