Low harmonic telephone ringing generator

Claim 2

A ringing generator for communication equipment, comprising an output transformer for supplying a signal to a load, said transformer having plural primary windings, a DC power source connected for providing a source of current to said plural primary windings, first and second control elements connected respectively to separate primary windings of said transformer, said control elements further being in connection with a further common primary winding, said control elements controlling current flow from said DC source through said respective primary windings, and means for alternately energizing said control elements for obtaining such controlled current flow to produce bidirectional current flow in said further common primary winding and unidirectional flow in said separate primary windings, thereby to develop an AC output voltage approximating a sinusoidal voltage in said output transformer.

Claim 3

A generator as set forth in claim 1 wherein said power source comprises positive and negative voltage terminals and a common terminal, said first control element being in series connection with one of said separate primary windings and said common winding between said positive and common terminals, said second control element being in series connection with another of said separate primary windings and said common winding between said negative and common terminals.

Claim 4

A generator as set forth in claim 2 wherein said energizing means comprises an oscillator including said first and second control elements for alternate energization thereof.

Claim 5

A generator as set forth in claim 3 wherein said control elements comprise transistors having collector-emitter paths in the series connection between said power terminals and said common terminal and base electrodes energized by said oscillator.

Claim 6

A generator as set forth in claim 4 wherein said transistors comprise an NPN transistor and a PNP transistor having directly coupled emitter electrodes.

Claim 7

A generator as set forth in claim 3 further including a feedback winding on said transformer, said feedback winding being interconnected with said oscillator for providing output voltage Regulation.

Claim 8

A generator as set forth in claim 6 wherein said feedback winding is in connection with said common terminal of said power supply and is poled to develop a voltage of opposite polarity to that voltage occurring in said common winding.

Claim 9

A generator as set forth in claim 7 further including current limiting means responsive to the sum of the voltages occurring in said feedback and said common windings and operatively connected with said control elements for controlling current flow therein.

Claim 10

A generator as set forth in claim 8 wherein said current limiting means comprises variable impedance means in connection with said control elements for shunting the signal applied from said oscillator as a function of said voltage sum.

Claim 11

A generator as set forth in claim 9 wherein said control elements comprise complementary transistors and said variable impedance means comprise further complementary transistors having a common base connection, said current limiting means further comprising a voltage divider in connection with said common and said feedback windings for energizing said common base connection.

Claim 12

Apparatus for developing a regulated AC output voltage approximating a sinusoidal voltage from a DC power source for application to a load, comprising a transformer having first and second primary windings and a secondary winding adapted for connection to the load, said transformer further including a feedback winding, means for controllably connecting said DC power source respectively to said first and second primary windings in opposite polarities to produce a sinusoidal signal in said secondary winding, an oscillator including said means for controllably connecting for controlling the frequency of connection of same and the control of said DC power by magnitude of oscillator signal, said feedback winding being connected to said oscillator for modifying the amplitude of said oscillator signal for regulating the voltage in said secondary winding, whereby said oscillator including said means for controllably connecting determines connection of said DC power source to said primary windings to effect production of said AC output voltage in said secondary winding.

Claim 13

Apparatus for developing a regulated AC output voltage approximating a sinusoidal voltage from a DC power source for application to a load, comprising a transformer having first and second primary windings and a secondary winding adapted for connection to the load, said transformer further including a feedback winding, means for controllably connecting said DC power source respectively to said first and second primary windings in opposite polarities to produce a sinusoidal signal in said secondary winding, an oscillator including said means for controllably connecting for controlling the frequency of connection of same and the control of said DC power by magnitude of oscillator signal, said feedback winding being connected to said oscillator for modifying the amplitude of said oscillator signal for regulating the voltage in said secondary winding, whereby said oscillator including said means for controllably connecting determines connection of said DC power source to said primary windings to effect production of said AC output voltage in said secondary winding.

Claim 14

Apparatus as set forth in claim 11 wherein said DC power source comprises positive, negative and common terminals, said transformer further comprises a common primary winding coupled to said common terminal and to said means for controllably connecting, said feedback winding being connected to said common terminal and being poled to develop a voltage in opposition to the voltage occurring in said common primary winding.

Claim 15

Apparatus as set forth in claim 12 wherein said oscillator comprises a frequency determinative feedback network, said network being adapted to receive the signal from said feedback winding.

Claim 16

Apparatus as set forth in claim 13 wherein said oscillator is a Wien-bridge type oscillator operative at a single frequency of oscillation.

Claim 17

Apparatus as set forth in claim 12 wherein said means for controllably connecting comprises NPN and PNP transistors having emitter electrodes connected in common and to said common primary winding and collector electrodes operatively connected respectively to said positive and negative terminals of said power source.

Claim 18

Apparatus as set forth in claim 15 wherein said first primary winding of said transformer is in series connection between said postive terminal and the collector electrode of said NPN transistor and said second primary winding of said transformer is in series connection between said negative terminal and the collector electrode of said PNP transistor.

Claim 19

Apparatus as set forth in claim 16 further including means for summing the voltages occurring in said common primary winding and in said feedback winding, and means operative in response to said voltage sum for limiting current flow in said means for controllably connecting.

Claim 20

Apparatus as set forth in claim 17 wherein said limIting means comprises complementary transistors in shunt connection with the base-emitter paths of said means for controllably connecting.