Loop and Ring Current Detector
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
In the interconnection of an electronic private automatic telephone exchange (PABX) to a central office (CX), it is necessary to detect loop and ringing currents in the trunk and reversed loop currents, as well. However, the use of high voltage, large capacitors for ring circuits and dial spark quenching is a drawback. The circuit described in this article consists of two optocouplers connected in opposite directions, one for each current flow direction. Optocoupler diodes A and B are in series with tip lead T. The currents through A and B are limited by diodes and resistors connected in parallel, as shown in [*]; therefore, these protecting elements are not represented in the above figure. Diodes A' and B' protect A and B against reverse currents.