Browse Prior Art Database

Triac Control in Telephone Circuits

IP.com Disclosure Number: IPCOM000086978D
Original Publication Date: 1976-Nov-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 70K

Publishing Venue

IBM

Related People

Feth, GC: AUTHOR [+2]

Abstract

In ordinary telephone circuits, for instance, in a CX or PBX, DC bias currents and AC ring currents must be controllably switched to the telephone extensions, and audio signals must be switched onto appropriate paths. While semiconductor circuits have been used as the crosspoints to switch the audio signals and DC bias, it has been impractical to switch the bidirectional ring current through the crosspoint. Described below is the use of triac devices both for crosspoints and for switching the DC and ring powering circuits controllably.

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Triac Control in Telephone Circuits

In ordinary telephone circuits, for instance, in a CX or PBX, DC bias currents and AC ring currents must be controllably switched to the telephone extensions, and audio signals must be switched onto appropriate paths. While semiconductor circuits have been used as the crosspoints to switch the audio signals and DC bias, it has been impractical to switch the bidirectional ring current through the crosspoint. Described below is the use of triac devices both for crosspoints and for switching the DC and ring powering circuits controllably.

Fig. 1 shows the subscriber telephone lines, the line circuits, the crosspoint- array concentrator, the audio isolation network, and the DC and ring powering circuits. Connection between a given pair of subscriber lines 10 and 12 and the pair of concentrated lines 14 and 16, which lead to the audio-isolation transformer 18, is accomplished by switching the appropriate crosspoint triacs 20 and 22 on from their respective gates. DC bias is supplied by switching triacs 28 and 30 on from their respective gates, in order to power a telephone which has gone off-hook. Alternatively, ring current plus DC bias is supplied by switching triacs 24 and 26 on from their gates in order to ring a selected telephone.

The triacs will carry current in either direction and can be gated on for either polarity of applied terminal voltage. However, they cannot be turned off, or returned to the blocking state, generally, from their gate terminals; they cease conducting when their main-terminal current falls in magnitude to a value less than the holding current of the triac and when there is no gate cur...