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Browse Prior Art Database

Subscriber Telephone Line Circuit

IP.com Disclosure Number: IPCOM000095207D
Original Publication Date: 1965-Oct-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Croisier, A: AUTHOR

Abstract

This subscriber line circuit reduces the DC current through the subscriber transformer as well as the AC power level. The circuit comprises two halves L and L' having similar configuration and operation. Only half L is described.

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Subscriber Telephone Line Circuit

This subscriber line circuit reduces the DC current through the subscriber transformer as well as the AC power level. The circuit comprises two halves L and L' having similar configuration and operation. Only half L is described.

The combination of diode D and transistors T1 and T2 derives the DC which would otherwise flow through winding W of the primary of transformer TR. Should beta be the gain of each transistor, the DC through W is reduced in the ratio beta/2/+2beta+1. Thus a reduction of five hundred can be realized. Capacitor C is added in order to derive the voice frequencies from the transistors and avoid undesired negative feedback.

The combination of T1 and T2 and resistors R1 and R2 acts as an operational amplifier. This action is in such a way that AC currents i1 and i2 flowing respectively through line 1 and winding W satisfy the relation i2 approximately=i1 R2/(R1+R2) without substantial variation of voltage level. Thus, with R1 = 90 omega, and R2 = 10 omega, AC power can be reduced in the ration of one-tenth.

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