Telephone ringing control circuits

Abstract

A single channel carrier system is disclosed including a remote terminal having a battery charger for charging a battery during idle periods to power the remote carrier electronics. The remote electronics include a ringing generator and a supervisory circuit to implement normal telephone supervision over the carrier channel. The ringing generator is a dc-to-dc converter for stepping the battery voltage up to the ringing voltage level. In order to interrupt this unipolar ringing voltage and thereby to energize the telephone ringer, a switching circuit is provided including a transistor in shunt with the ringing voltage supply to provide a return path for alternate half cycles of ringing current. A constant current source from a low voltage supply connected to the base of the transistor provides bias current to saturate the transistor yet minimizes the amount of dissipated power.

Dependencies are inferred from the claim text.