Electronic ring trip circuit
AssigneeInternational Telephone and Telegraph Corporation
InventorsPhillip L. Holmes, Frank Cinkus, John Hugh Green
Life of this patent
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Abstract
Disclosed is an electronic ring trip circuit which does not require the use of an electromagnetic ring trip relay. The circuit employs an optical coupler as the offhook detector to act on an essentially bi-stable operational amplifier which is normally in a ring enabling state. With the amplifier in this state, the circuit responds to ring current and a ring connect relay is enabled by the circuit for operation. When the called station goes off-hook, the amplifier is switched to its ring trip state and disables the ring connect relay. An input circuit for the ring current shunts this AC away from the optical coupler to render the coupler responsive to minor changes in DC resulting from the called station going off-hook.
Claims7
A ring control circuit for a telephone line to which alternating current ringing signals are applied from a ring signal source, including a ring connect relay operated responsive to ring signal input to close a path from said source to said telephone line and to a ring trip portion of said circuit, means for latching said relay in its operated condition, direct current detecting means responsive to rectified alternating current ring signals for maintaining the charge on a capacitor beyond a threshold level, means responsive to direct current through said line resulting from a closed loop condition of said line for causing the direct current and superimposed rectified ringing current to cause the charge on said capacitor to pass said level, an operational amplifier responsive to the charge of said capacitor passing said threshold for changing condition to release said latching means to cause release of said relay, said relay on release opening the closed path, and means for latching said amplifier in said changed condition.
A ring control circuit for a telephone line to which alternating current ringing signals are applied from a ring signal source, including a ring connect relay operated responsive to ring signal input to close a path from said source to said telephone line and to a ring trip portion of said circuit, a first transistor conductive to latch said relay in its operated condition, current detecting means responsive to rectified alternating current ring signals for maintaining the charge on a capacitor above a threshold level, means responsive to direct current through said line resulting from a closed loop condition of said line for causing the direct current and superimposed rectified ringing current to discharge said capacitor below said level, an operational amplifier responsive to discharge of said capacitor below said threshold for changing to a tripped condition to release said latching transistor and cause release of said relay, said relay on release opening the ringing path to said current detecting means, a second transistor for latching said amplifier in said changed condition, and said current detector responsive to the cessation of ring current over said opened path to restore said amplifier from its tripped condition.
Dependencies are inferred from the claim text.