Electronic ring trip circuit

Claim 1

In a ring cut-off arrangement of the type comprising switching means interposed in the ringing circuit to operate in response to said circuit being traversed by direct current, but to remain unoperated when said circuit is traversed by alternating ringing current alone, the improvement being that said switching means comprises: first and second light emitting diodes connected in inverse parallel in series in said ringing circuit to alternately glow as they alternately conduct the ringing signal, and only one of them glow during the flow of a direct current in said circuit, a source of operating potential having a first and a second terminal, a first and a second resistor in series and connected across said operating potential terminals, a capacitor connected at one end to said first one of said operating potential terminals, and means connecting the other end of said capacitor intermediate said first and second resistors whereby said capacitor is maintained at a first nominal charge level by said resistors, first and second two terminal light sensitive switch means of the type adapted to be rendered conductive when illuminated, respectively operatively associated with said light emitting diodes and connected in series across said operating potential terminals, other means connecting the junction of said two light sensitive switch means to the other end of said capacitor, said light sensitive switches responding to the glow from said associated diodes to alternately raise and lower the nominal charge state of said capacitor during the flow of an alternating current in said circuit, only one of them remaining conductive to increase the charge of said capacitor during the flow of a direct current in said circuit, and switch means responsive to the increased charge of said capacitor to remove said ringing current from said circuit.