Ground fault circuit interrupting device with improved coordination of electronic circuit operation

Claim 1

An integrated circuit for utilization in a ground fault circuit interrupting device including a differential current transformer having a secondary winding in which is developed a fault signal proportional to any imbalance in the currents flowing in the line and neutral conductors of an AC power distribution circuit occasioned by a line to ground fault, a neutral transformer having a primary winding which is driven to develop a differential transformer imbalancing current in the neutral conductor if faulted to ground through a desensitizing low impedance, separable contacts for interrupting at least the line side of the distribution circuit, a trip solenoid, a thyristor operating when triggered into conduction to draw activating current through the solenoid to initiate separation of the contacts, an integrating capacitor and an energy storage filter capacitor, said integrated circuit comprising, in combination: A. a differential amplifier having a first input connected with the differential current transformer secondary winding for amplifying a fault signal developed therein by a current imbalance exceeding a pre-selected threshold level established by a bias voltage applied to a second amplifier input, said amplifier developing an integrating capacitor charging current of a magnitude exponentially related to the fault signal magnitude; B. an oscillator connected to drive the primary winding of the neutral transformer; C. a comparator for sensing the voltage developing across the integrating capacitor; D. a thyristor gate driver controlled by said comparator for producing gate pulses to trigger the thyristor into conduction when the voltage across the integrating capacitor achieves a pre-established reference level; E. a clamp connected with said gate driver for inhibiting the triggering of the thyristor; and F. a power supply including (1) a first diode conducting half-cycle line current from the distribution circuit onto a first power supply bus, (2) a regulating means connected with said bus for establishing a regulated supply voltage thereon during a substantial portion of each conducting half-cycle of said first diode, (3) means responsive to said regulating means for (a) conditioning said clamp to inhibit triggering of the thyristor while the supply voltage is in regulation, (b) turning on said oscillator while the supply voltage is in regulation, and (c) strobing said comparator as said supply voltage achieves regulation to determine if the voltage across the integrating capacitor has achieved said pre-established reference level.