Solid state tripping circuit

Apparatus for interrupting a current flowing in a circuit having a normal rated current, comprising:

• means for interrupting the continuity of said circuit;
• means coupled to said circuit for generating a signal current proportional to a peak of said circuit current;
• rating circuit means for generating a signal voltage proportional to siad peak current, the magnitude of said signal voltage being selected to be at a first predetermined value when said circuit current is equal to said rated current;
• means for generating a trigger signal responsive to a predetermined relationship between said signal voltage and a time duration during which said signal voltage is present, said trigger signal generating means comprising first means for generating a first output signal substantially instantaneously responsive to said signal voltage exceeding a second predetermined value greater than said first value, second means for generating a second output signal in accordance with a first selected curve of the inverse of said signal voltage versus the time duration during which said signal voltage exists;
• third means for generating a third output signal in accordance with a predetermined inverse relationship between the square of the signal voltage and the time duration during which said signal voltage exists;
• and means for combining said first, second and third output signals to couple at least the first occurring output signal to an actuating means;
• said actuating means being responsive to said trigger signal for actuating said circuit continuity interrupting means to terminate current flow in said circuit;
• pick-up means for preventing said first, second and third means from reacting to a signal voltage less than a third predetermined value, said third value being greater than said first predetermined value and less than said second value, to prevent interruption of the continuity of said circuit for any flow of circuit current having a ratio to the normal rated current equal to the ratio of said third value to said first value;
• said actuating means being a first switching element having a control electrode receiving said trigger signal, said first switching element adapted to activate said interrupting means when said trigger signal is present at said control electrode;
• said third means comprising fourth means for storing a variable amount of an electrical quantity;
• fifth means for adding to said fourth means amounts of said electrical quantity substantially equal to the square of said signal voltage;
• and sixth means for comparing the amount of said electrical quantity stored in said fourth means to a fifth predetermined value and for generating said third output signal when the stored amount exceeds said fifth value;
• said fourth means being a capacitive element;
• and said fifth means being a current source having an input receiving said signal voltage and an output, said output being coupled to said capacitive element and adapted to cause a flow of charge thereto varying substantially as the square of said signal voltage at said input of said current source;
• and
• said current source including a source of an essentially constant reference voltage;
• a semiconductor element having base, collector and emitter electrodes, said base electrode receiving said reference voltage from said source, said collector electrode coupled to said capacitive element;
• a non-linear resistance network coupled between said emitter electrode and said current source input, the resistance of said non-linear network being dependent upon the magnitude of the signal voltage across said non-linear network and approximating the square of the inverse of said signal voltage to generate a current to said capacitive element having said predetermined inverse relationship.