Ring trip circuit employing a filter network and a solid state device exhibiting electrical isolation

Claim 2

A ring trip circuit for use in a telephone series ringing circuit, the series circuit including a telephone line, at least one telephone instrument connected thereto, a ringing generator for providing AC ringing signals to operate a signalling device in the telephone instrument to indicate a telephone call on the line and a battery for providing a DC current when the call is answered, comprising an optoelectronic coupler having an input circuit for producing a signal proportional to the current therethrough and an output circuit electrically isolated from said input circuit whose conductivity state is a function of said signal, a delay circuit connected across the output circuit of the optoelectronic coupler and a parallel-T resistancecapacitance network having a first pair of terminals for connection in the series circuit and a second pair of terminals for connection to said input circuit, said network providing two current paths, one for passing the ringing signals while blocking DC current and the other for passing DC current through said input circuit to the substantial exclusion of the ringing signals.

Claim 3

The ring trip circuit of claim 1 including circuit means connected across said first pair of terminals to provide a low impedance AC path therebetween.

Claim 4

The ring trip circuit of claim 2 wherein said circuit means is a capacitor.

Claim 5

The ring trip circuit of claim 1 wherein said filter network comprises a pair of T networks connected in parallel, each having first, second and third terminals, the second terminal of each leading to the middle leg of the T network, arranged so that said first and second terminals constitute said first pair of terminals of said filter network and said second and third terminals constitute said second pair of terminals of said filter network.

Claim 6

The ring trip circuit of claim 1 wherein a first one of said pair of T networks consists of a capacitor in its middle leg and resistors in its other two legs and the other one of said pair of T networks consists of a resistor in its middle leg and capacitors in its other two legs.

Claim 7

The ring trip circuit of claim 5 including a capacitor connected across said first and second terminals to provide a low impedance AC path therebetween.

Claim 8

A ring trip circuit for use in a telephone series ringing circuit, the series circuit including a telephone line, at least onE telephone instrument connected thereto, a ringing generator for providing AC ringing signals to operate a signaling device in the telephone instrument to indicate a telephone call on the line and a battery for providing a DC current when the call is answered, comprising: an optoelectronic coupler having an input circuit for producing a signal proportional to the current therethrough and an output circuit electronically isolated from said input circuit whose conductivity state is a function of said signal; a delay circuit connected across the output circuit of the optoelectronic coupler; a filter network having a first pair of terminals for connection in the series circuit and a second pair of terminals for connection to said input circuit, said network providing two current paths, one for passing the ringing signals while blocking DC current and the other for passing DC current through said input circuit to the substantial exclusion of the ringing signal, and a capacitor connected across said first pair of terminals to provide a low impedance AC path therebetween; said filter network comprising a pair of T networks connected in parallel each having first, second, and third terminals, the second terminal of each leading to the middle leg of the T network, arranged so that said first and second terminals constitute said first pair of terminals of said filter network and said second and third terminals constitute said second pair of terminals of said filter network, the first of said pair of T networks consisting of a capacitor in its middle leg and resistors in its other two legs, and the other one of said pair of T networks consisting of a resistor in its middle leg and capacitors in its other two legs.

Claim 9

A ring trip circuit for use in a telephone series ringing circuit, the series circuit including a telephone line, at least onE telephone instrument connected thereto, a ringing generator for providing AC ringing signals to operate a signaling device in the telephone instrument to indicate a telephone call on the line and a battery for providing a DC current when the call is answered, comprising: an optoelectronic coupler having an input circuit for producing a signal proportional to the current therethrough and an output circuit electronically isolated from said input circuit whose conductivity state is a function of said signal; a delay circuit connected across the output circuit of the optoelectronic coupler; a filter network having a first pair of terminals for connection in the series circuit and a second pair of terminals for connection to said input circuit, said network providing two current paths, one for passing the ringing signals while blocking DC current and the other for passing DC current through said input circuit to the substantial exclusion of the ringing signal, and a capacitor connected across said first pair of terminals to provide a low impedance AC path therebetween; said filter network comprising a pair of T networks connected in parallel each having first, second, and third terminals, the second terminal of each leading to the middle leg of the T network, arranged so that said first and second terminals constitute said first pair of terminals of said filter network and said second and third terminals constitute said second pair of terminals of said filter network, the first of said pair of T networks consisting of a capacitor in its middle leg and resistors in its other two legs, and the other one of said pair of T networks consisting of a resistor in its middle leg and capacitors in its other two legs.