Call and feed voltage supply for PBX telephone appts. - feeds DC potential in rest and call states to subscriber line pair via different paths, under microprocessor control

摘要

The PBX is microprocessor controlled, and the telephone appts has a series connection of a bell and a capacitor in rest and call states. In the speech state, the speech circuit is incorporated between both speech cores. A local feed DC voltage is earthed. In the rest and call states, the potential of the feed DC voltage (U) is applied to one speech core (a) via a current source (SQ) and via a first current sink (SS1) the earth potential is linked to the other core (b). In the cell state, alos second current sink (SS2) is so controlled by the microprocessor (M) call pulses so that it disconnects the current source in the call pulse cycle. It connects the second core to the feed potential via an electronic switch (5), and the first core to the earth potential. ADVANTAGE - No need for relays and chokes for call signal disconnection.