Protection circuit for capacitive ballast
First Claim
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1. A load protection circuit for use with a ballast having, across an A.C. source, a capacitive element in series with a substantially resistive load and a switching device, comprising:
- means for detecting a load current zero crossing; and
means for sampling the magnitude of current flowing through said load at a time after the detected load current zero crossing, and for disabling said switching device to prevent substantial load current flow therethrough only if said load current magnitude is of substantially zero magnitude when sampled.
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Abstract
A protection circuit for a capacitively ballasted load provides decreased load current in the event of a circuit arc. The A.C. load current is measured at a time shortly after a load current zero crossing; if a non-zero load current is present, the load is operating normally and no action is taken, whereas if the load current remains at an essentially zero magnitude, indicative of circuit arcing conditions, normal load operation is inhibited.
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14 Claims
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1. A load protection circuit for use with a ballast having, across an A.C. source, a capacitive element in series with a substantially resistive load and a switching device, comprising:
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means for detecting a load current zero crossing; and means for sampling the magnitude of current flowing through said load at a time after the detected load current zero crossing, and for disabling said switching device to prevent substantial load current flow therethrough only if said load current magnitude is of substantially zero magnitude when sampled. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification