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Browse Prior Art Database

Junctor Scanning of DC Pulses in a PBX

IP.com Disclosure Number: IPCOM000093453D
Original Publication Date: 1967-Sep-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Poulet, A: AUTHOR

Abstract

This circuit is for transmitting DC pulses from telephone lines to junctors and for detecting the pulses on the junctors. A telephone line is connected between -48 volts and ground. Each telephone line is connected to the switching network through a line transformer TR.

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Junctor Scanning of DC Pulses in a PBX

This circuit is for transmitting DC pulses from telephone lines to junctors and for detecting the pulses on the junctors. A telephone line is connected between - 48 volts and ground. Each telephone line is connected to the switching network through a line transformer TR.

As soon as a new call is detected, a path is established between the calling extension and a free junctor through the switching network. Three SCR's, SCR1, SCR2, SCR3, are switched on. The path being established, the DC pulses are transmitted from the line to the junctor and detected at the junctor level. This junctor is principally composed of transistor T4 and a feeder. In the transmission of the DC line pulses, the bus current of the SCR's is generated via two different paths from a +V voltage, through a saturated PNP transistor T1, subscriber off- hook, and through a resistor R, subscriber on-hook.

When the subscriber is off-hook, the line current saturates T2.

A current flows through R1 and R2. This current, through resistor R1, saturates T1 and the SCR's bias current flows through T1. When the subscriber is on-hook, T2 is reverse biased and T1 is also reverse biased. Thus SCR's bias current flows through R. The DC line pulses are thus transmitted to the junctor through the network and can be detected at this level. R is such that the voltage on the collector of the feeder, point A, is under a voltage Vo.

This voltage Vo is clamped by a clamping circuit...