Inverse overcurrent-time delay circuit protective device utilizing nonlinear resistance

Claim 1

A PROTECTIVE CIRCUIT FOR INITIATING OPERATION OF A CIRCUIT BREAKER TO OPEN A LINE UPON THE OCCURRENCE OF AN OVERCURRENT CONDITION, SAID CIRCUIT COMPRISING: (A) A UNIJUNCTION TRANSISTOR FOR INITIATING OPENING OPERATION OF THE CIRCUIT BREAKER IN RESPONSE TO THE OCCURRENCE OF A PREDETERMINED OVERCURRENT CONDITION IN THE LINE, SAID TRANSISTOR HAVING AN EMITTER, FIRST BASE AND SECOND BASE ELECTRODES; (B) TIMING MEANS HAVING A PREDETERMINED FIXED TIME CONSTANT CONNECTED TO THE EMITTER OF SAID UNIJUNCTION TRANSISTOR FOR CONTROLLING THE CONDUCTIVE STATE OF THE TRANSISTOR; (C) MEANS RESPONSIVE TO THE CURRENT IN THE LINE FOR DEVELOPING ACROSS TWO PARALLEL VOLTAGE DIVIDERS A DC CONTROL VOLTAGE PROPORTIONAL TO SAID CURRENT, (I) ONE OF SAID VOLTAGE DIVIDERS INCLUDING A ZENER DIODE TO ESTABLISH A REFERENCE VOLTAGE AT AN INTERMEDIATE POINT OF SAID ONE DIVIDER, AND (II) THE OTHER VOLTAGE DIVIDER INCLUDING A NONLINEAR RESISTANCE, THE OHMIC VALUE OF WHICH INCREASES AS THE MAGNITUDE OF CURRENT PASSING THERETHROUGH INCREASES, TO ESTABLISH A MODIFIED DC CONTROL VOLTAGE AT AN INTERMEDIATE POINT OF SAID OTHER DIVIDER;