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Solid State Telephone Switch

IP.com Disclosure Number: IPCOM000079694D
Original Publication Date: 1973-Aug-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Glowienka, CB: AUTHOR

Abstract

This circuit provides an all solid-state switch for the control of a telephone on an extension line. This provides for electronic removal f the telephone so that another device, not shown, may be connected in parallel on the same extension. The salient features of the switch are: 1) If logic power fails the telephone automatically reconnects to the extension line. 2) The switch is insensitive to extension line polarity. 3) Ringing voltages, alternating or DC pulse, are passed. 4) The telephone may be of the pulse dialing type or multi-frequency tone dialing type.

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Solid State Telephone Switch

This circuit provides an all solid-state switch for the control of a telephone on an extension line. This provides for electronic removal f the telephone so that another device, not shown, may be connected in parallel on the same extension. The salient features of the switch are:

1) If logic power fails the telephone automatically reconnects

to the extension line.

2) The switch is insensitive to extension line polarity.

3) Ringing voltages, alternating or DC pulse, are passed.

4) The telephone may be of the pulse dialing type or

multi-frequency tone dialing type.

Even though a voltage of reversing polarity may appear at the input terminals of the diode bridge. the polarity at the output terminals is fixed as indicated. With no conducting device across the output terminals, the telephone loop is open. Transistor Q1, when turned ON, provides a low-resistance path between the output terminals, thus closing the telephone loop. Q3 is normally OFF.

Establishing a closed loop with the telephone going off-hook is as follows:

Lifting the handset causes the transmission unit in the telephone to be connected across the telephone terminals via the hook switch. The bridge input terminals see the extension line voltage. The bridge output terminals provide this voltage, but polarized as indicated. A current flows through R1 to the base of Q2 turning it ON. The current is multiplied by the beta of Q2 and provided to the base of Q1, turning it ON to s...