Electronic ring trip circuit

摘要

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.