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AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorFrank J. Nola
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A failure detector is provided for detecting unidirectional failures in triacs, particularly as used in power factor controllers for induction motors. In a first embodiment, the triac voltage waveform is sensed and upon detection of an unbalanced signal, corresponding to failure of the triac in either the positive or negative direction, the triac is turned full on in both directions. In a second embodiment, a pair of pulsed signals are derived, the pulse durations of which are proportional to the phase difference between the load current and voltage for each half cycle, and the triac is turned full on responsive to a difference in pulse duration between the half cycle signals. An unidirectional open circuit detector is adapted to use a signal from either of the first and second embodiments to turn the triac off in response to an open circuit failure in either direction.
In a triac control system for controlling current flow to a load, a triac failure detection circuit for detecting a unidirectional short circuit failure of the triac control system, said failure detection circuit comprising detecting means for detecting the triac voltage waveform and for producing a first output responsive to a symmetrical triac voltage waveform produced during normal triac operation and for producing a second output responsive to a non-symmetrical triac voltage waveform caused by failure of said triac in either a positive or negative direction;
In a triac control system for an alternating current input signal for controlling input current flow to an inductive load, a triac failure detection circuit for detecting a unidirectional short circuit failure of the traic of the control system, said failure detection circuit comprising phase shift detection means for deriving first and second pulse trains of phase difference pulses whose phase durations are proportional to the phase differences between the triac voltage and current for each half cycle of said alternating current signal, and detecting means for receiving said phase difference pulses and for producing a first output when the half cycle pulses are of equal duration corresponding to normal operation, and for producing a second output when the half cycle pulses are of unequal duration corresponding to a short circuit failure of said triac in either direction, and control means, connected to said detecting means, for turning said triac full on in both directions responsive to said second output.
Dependencies are inferred from the claim text.