Coupling network for speech conductor in telephone exchange - has pair of series connected transistor circuits between lines as constant current source

摘要

A speech conductor coupling network which is used in telepling exchange equipment fitted in each case with the coupling contacts needed for a holding current. The conductor strands connected to such coupling networks are linked to direct current circuits with high differential resistance. These lines incorporate switching elements whose conducting characteristics are dependent on the direction of flow of the current. In each case two lines (A, B) are linked in pairs with a direct current circuit (Sa, Sb) associated with each line. The direct current circuits which consist of transistors are connected in series between the two lines. The control electrodes of the two circuits are interconnected. These circuits form constant current sources which are maintained by linking the control electrode to a reference potential (PR).