Telephone line circuit embodying a triggerable avalanche device

Claim 2

A telephone line circuit for serving key telephones in a key telephone system comprising a pair of line conductors, relay circuit means for detecting current therethrough and for connecting a dummy load across the line conductors for placing said line in a hold condition, and circuit means including a triggerable avalanche device for causing said relay circuit means to place said line in a hold condition in response to a hold signal from a key telephone and for causing said relay circuit means to positively release said line from the hold condition upon detection by said relay circuit means of a momentary interruption of line current or polarity reversal in line potential.

Claim 3

A telephone line circuit as defined in claim 1 wherein said relay circuit means is responsive to the conduction of the triggerable avalanche device to place the line in hold and said circuit means renders said device non-conductive to cause the relay means to release the line from hold in response to the momentary line current interruption or line potential polarity reversal.

Claim 4

A telephone line circuit as defined in claim 2 wherein said relay circuit means includes a relay connected iN series with said pair of line conductors and said device is connected in series with contacts of said relay whereby said device is rendered conductive when said relay is actuated and said hold signal is present and is rendered non-conductive when said relay is momentarily deactuated.

Claim 5

A key telephone line circuit for connecting a key telephone set to a telephone line from a switching exchange comprising: a key telephone set including at least one line key, at least one hold key and signalling means; first, second and third relays; a triggerable avalanche semiconductor device; a pair of line conductors for connecting the telephone line to the key telephone set through contacts of said line key; circuit means connecting said first relay to said pair of conductors so that said first relay is energized by either ringing signals or by a D.C. current flow through the telephone line; circuit means connected so that said second relay is energized through contacts of said first relay when said first relay is actuated by ringing signals wherein contacts of said second relay are actuated to activate said signalling means; circuit means responsive to when said telephone set goes off hook and the line key is actuated for actuating said third relay and deactuating said second relay; a dummy load for connection across said pair of conductors through contacts of said second and third relays, and circuit means responsive to the actuation of the hold key for actuating said third relay through said device and for actuating said second relay thereby connecting said dummy load across said pair of conductors to place the line in a hold condition and wherein a momentary polarity reversal in potential across said conductors or interruption in line current sufficient to momentarily drop out the first relay cuts off the triggerable avalanche device and deactivates the second and third relays.

Claim 6

A key telephone line circuit for connecting a key telephone set to a telephone line from a switching exchange comprising: a key telephone set including at least one line key, at least one hold key and signalling means; first, second and third relays; a triggerable avalanche semiconductor device; a pair of line conductors for connecting the telephone line to the key telephone set through contacts of said line key; circuit means connecting said first relay to said pair of conductors so that said first relay is energized by either ringing signals or by a D.C. current flow through the telephone line; circuit means connected so that said second relay is energized through contacts of said first relay when said first relay is actuated by ringing signals wherein contacts of said second relay are actuated to activate said signalling means; circuit means responsive to when said telephone set goes off hook and the line key is actuated for actuating said third relay and deactuating said second relay; a dummy load for connection across said pair of conductors through contacts of said second and third relays, and circuit means responsive to the actuation of the hold key for actuating said third relay through said device and for actuating said second relay thereby connecting said dummy load across said pair of conductors to place the line in a hold condition and wherein a momentary polarity reversal in potential across said conductors or interruption in line current sufficient to momentarily drop out the first relay cuts off the triggerable avalanche device and deactivates the second and third relays.

Claim 7

A key telephone line circuit for connecting a key telephone set to a telephone line from a telephone switching exchange comprising: a pair of line conductors for connecting the telephone line from the exchange to said telephone set for transmitting voice signals; a first relay circuit connected to said pair of line conductors for energization by either ringing signals from said exchange or by a D.C. current flow through the telephone line; a second relay circuit responsive to the actuation of said first relay for applying ringing signals to said telephone; a third relay circuit including a triggerable avalanche device for actuation in response to an off hook condition in said telephone set; a dummy load circuit for connection across said line conductors through contacts of said second and third relay circuits, and circuit means responsive to the operation of the hold button in said telephone set for maintaining said third relay circuit actuated through said triggerable avalanche device and for actuating said second relay circuit means whereby said dummy load is connected across said pair of conductors, the arrangement being such that the triggerable avalanche device is responsive to a momentary deactuation of said first relay circuit to deactivate said second and third relay circuits and release said dummy load.

Claim 8

A key telephone line circuit for connecting a key telephone set to a telephone line from a telephone switching exchange comprising: a pair of line conductors for connecting the telephone line from the exchange to said telephone set for transmitting voice signals; a first relay circuit connected to said pair of line conductors for energization by either ringing signals from said exchange or by a D.C. current flow through the telephone line; a second relay circuit responsive to the actuation of said first relay for applying ringing signals to said telephone; a third relay circuit including a triggerable avalanche device for actuation in response to an off hook condition in said telephone set; a dummy load circuit for connection across said line conductors through contacts of said second and third relay circuits, and circuit means responsive to the operation of the hold button in said telephone set for maintaining said third relay circuit actuated through said triggerable avalanche device and for actuating said second relay circuit means whereby said dummy load is connected across said pair of conductors, the arrangement being such that the triggerable avalanche device is responsive to a momentary deactuation of said first relay circuit to deactivate said second and third relay circuits and release said dummy load.

Claim 9

A telephone line circuit for placing a telephone line serving a key telephone in and out of hold conditions comprising: a monitor circuit including a monitor relay which is energized by d.c. current flow in the telephone lines; circuit means including a triggerable avalanche device and a first hold relay arranged so that in response to a hold signal from the key telephone said first hold relay is energized through a series path including said device and a contact of said monitor relay; circuit means for applying a gating signal to turn on said device prior to a hold condition and for removing said gating signal after the initiation of the hold condition; a second hold relay; circuit Means for energizing said second hold relay through contacts of said first hold relay in response to said hold signal; a dummy load, and circuit means including contacts of said first and second hold relays for connecting said dummy load across the telephone line when both said first and second hold relays are energized.

Claim 10

A telephone line circuit for placing a telephone line serving a key telephone in and out of hold conditions comprising: a monitor circuit including a monitor relay which is energized by d.c. current flow in the telephone lines; circuit means including a triggerable avalanche device and a first hold relay arranged so that in response to a hold signal from the key telephone said first hold relay is energized through a series path including said device and a contact of said monitor relay; circuit means for applying a gating signal to turn on said device prior to a hold condition and for removing said gating signal after the initiation of the hold condition; a second hold relay; circuit Means for energizing said second hold relay through contacts of said first hold relay in response to said hold signal; a dummy load, and circuit means including contacts of said first and second hold relays for connecting said dummy load across the telephone line when both said first and second hold relays are energized.

Claim 11

The line circuit of claim 6 wherein said monitor relay is energized by ringing signals and said second hold relay is energized through a contact of said monitor relay in response to the ringing signals.

Claim 12

The line circuit of claim 7 wherein said second hold relay is de-energized by an off hook signal generated in the key telephone when a telephone call is answered.

Claim 13

The line circuit of claim 6 wherein said first hold relay is energized by an off hook signal generated in the key telephone whenever a talking path through the telephone line is completed via the telephone.

Claim 14

A control circuit for providing a positive release of a telephone line while on hold, the telephone line being connected to a key telephone set through a line circuit having a line relay which is actuated by current through the telephone line and a first relay which is actuated for connecting a dummy load across the telephone line in response to a hold signal from the telephone set to effectuate a hold condition, said control circuit comprising: a triggerable avalanche device; circuit means for providing a first current path to said avalanche device; circuit means for applying a gating signal to said avalanche device to render it conductive through said first current path when the telephone set is connected to the telephone line and for removing the gating signal in response to the hold signal, and circuit means for energizing the first relay through said avalanche device and contacts of the line relay during a hold condition.

Claim 15

A control circuit for providing a positive release of a telephone line while on hold, the telephone line being connected to a key telephone set through a line circuit having a line relay which is actuated by current through the telephone line and a first relay which is actuated for connecting a dummy load across the telephone line in response to a hold signal from the telephone set to effectuate a hold condition, said control circuit comprising: a triggerable avalanche device; circuit means for providing a first current path to said avalanche device; circuit means for applying a gating signal to said avalanche device to render it conductive through said first current path when the telephone set is connected to the telephone line and for removing the gating signal in response to the hold signal, and circuit means for energizing the first relay through said avalanche device and contacts of the line relay during a hold condition.

Claim 16

The control circuit of claim 10 wherein the line circuit includes a second relay which is energized in response to said hold signal through contacts of the first relay and both the first and second relays are energized to connect the dummy load across the telephone line during a hold condition.

Claim 17

The control circuit of claim 11 wherein the first relay is operated whenever the key telephone set is connected to the telephone line and the second relay is operated whenever a ringing signal is applied to the telephone line.