Lamp ballast with lamp rectification detection circuitry
First Claim
1. A ballast for a gas discharge lamp, comprising a current limiting AC voltage source for maintaining a column discharge in the discharge lamp alternately with one polarity and with the opposite polarity, and a detection circuit for detecting asymmetry between the column discharge of one polarity and the column discharge of the opposite polarity, characterized in that:
- said detection circuit detects a DC voltage generated by the discharge lamp with asymmetry occurring between the column discharges of the one polarity and the opposite polarity; and
said detection circuit measures the amount of time the DC voltage is above a threshold value and changes the output of the current limiting AC voltage source after the measured amount of time exceeds a first threshold time value.
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Accused Products
Abstract
A ballast for a gas discharge lamp includes a detection circuit which detects an operating state of the lamp in which the lamp current for the column discharge of one polarity is different from the lamp current for the column discharge of the other polarity by detecting the DC component of the voltage across the discharge lamp. The detection circuit includes (i) a device coupled such that a DC voltage is imposed there across when the lamp current is different for the column discharge according to one polarity verses the other polarity, and (ii) a sensing circuit for sensing the DC voltage across the device. The device may be a capacitive device, and in a particularly inexpensive implementation, is a DC blocking capacitor or a ballast capacitor. The sense circuit senses when the DC voltage across the device exceeds a threshold value, which may corresponds to fully-rectified state of the lamp or more favorably, to a lesser state of imbalance. In another embodiment, the variance in the DC voltage across the lamp is detected at the midpoint of a bridge inverter. A control circuit changes the output of the ballasting circuit when the DC voltage exceeds the threshold value to turn off the lamp or to recurrently cycle the lamp on and off to signal the user that the lamp needs to be changed.
79 Citations
38 Claims
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1. A ballast for a gas discharge lamp, comprising a current limiting AC voltage source for maintaining a column discharge in the discharge lamp alternately with one polarity and with the opposite polarity, and a detection circuit for detecting asymmetry between the column discharge of one polarity and the column discharge of the opposite polarity, characterized in that:
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said detection circuit detects a DC voltage generated by the discharge lamp with asymmetry occurring between the column discharges of the one polarity and the opposite polarity; and said detection circuit measures the amount of time the DC voltage is above a threshold value and changes the output of the current limiting AC voltage source after the measured amount of time exceeds a first threshold time value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A method of operating a gas discharge lamp, said method comprising the steps of:
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a) providing an AC voltage across said discharge lamp for maintaining a column discharge in the discharge lamp alternately with one polarity and with the opposite polarity; b) detecting a DC voltage generated by an asymmetric operating state of the lamp in which the lamp current for the column discharge of one polarity is different from the lamp current for the column discharge of the other polarity; and c) measuring the amount of time that the DC voltage exceeds a threshold value, and changing the operation of the discharge lamp when said measured amount of time exceeds a first threshold time value. - View Dependent Claims (20, 21, 22, 23)
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24. A ballast for a gas discharge lamp, said ballast comprising:
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a) input terminals for connection to an AC mains supply having a mains supply frequency, b) output terminals for connection to a gas discharge lamp having a pair of discharge electrodes between which a column discharge is maintainable during lamp operation, c) ballasting means connected between said input terminals and said output terminals, said ballasting means providing an AC voltage at said output terminals to maintain a column discharge between the discharge electrodes of the discharge lamp alternately with one polarity and with the opposite polarity at a frequency substantially higher than the mains supply frequency, and d) detecting means for detecting a DC voltage generated by an asymmetric operating state of the lamp in which the lamp current for the column discharge of one polarity is different from the lamp current for the column discharge of the other polarity, said detecting means including means for measuring the amount of time that the DC voltage exceeds a threshold value and for changing the operation of the discharge lamp when said measured amount of time exceeds a first threshold time value. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A dimming ballast for a gas discharge lamp, said ballast comprising:
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mains input terminals for receiving an AC mains voltage; a full bridge rectifier connected to said input terminals for providing a full wave rectified DC output voltage; a pre-conditioner circuit connected to the full-bridge rectifier, said pre-conditioner circuit including an up converter for providing a DC supply voltage at a level higher than the peak voltage of the rectified DC output voltage from said full-bridge rectifier; an inverter circuit receptive of the DC supply voltage from said pre-conditioner circuit, said inverter converting the DC supply voltage from said preconditioner to a high frequency AC voltage having a frequency substantially greater than the frequency of the AC mains supply; a resonant tank output circuit receptive of the high frequency AC inverter output voltage, said output circuit having lamp connection terminals for connection to a gas discharge lamp, said output circuit providing a substantially sinusoidal lamp current to a gas discharge lamp connected at said lamp terminals for maintaining a column discharge between the discharge electrodes of the discharge lamp alternately with one polarity and with the opposite polarity; a control circuit connected to said inverter for controlling the AC inverter output voltage, said control circuit;
having (i) means for receiving a dimming signal (ii) means for sensing the power supplied to the gas discharge lamp, and (iii) means for adjusting the AC inverter output frequency fed to said resonant tank output circuit to thereby control the electrical power supplied to the gas discharge lamp at a level corresponding to the dimming signal; anddetecting means for detecting a DC voltage generated by an asymmetric operating state of the lamp in which the lamp current for the column discharge of one polarity is different from the lamp current for the column discharge of the other polarity, and means for measuring the amount of time that the DC voltage exceeds a threshold value to change the output of the inverter circuit when the amount of time exceeds a time threshold value. - View Dependent Claims (36)
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37. A ballast for a gas discharge lamp, comprising a current limiting AC voltage source for maintaining a column discharge in the discharge lamp alternately with one polarity and with the opposite polarity, and a detection circuit for detecting asymmetry between the column discharge of one polarity and the column discharge of the opposite polarity, characterized in that:
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said detection circuit detects a DC voltage generated by the discharge lamp with asymmetry occurring between the column discharges of the one polarity and the opposite polarity; and means, responsive to said detection circuit detecting a DC voltage exceeding a threshold value, for recurrently extinguishing and igniting the gas discharge lamp to cause said lamp to blink.
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38. A ballast for a gas discharge lamp, comprising a current limiting AC voltage source for maintaining a column discharge in the discharge lamp alternately with one polarity and with the opposite polarity, and a detection circuit for detecting asymmetry between the column discharge of one polarity and the column discharge of the opposite polarity, characterized in that:
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said detection circuit detects a DC voltage generated by the discharge lamp with asymmetry occurring between the column discharges of the one polarity and the opposite polarity; said detection circuit being coupled to said current limiting voltage source for changing the output of said voltage source when said DC voltage exceeds a threshold value; said current limiting AC voltage source controlling the light level emitted by the discharge lamp between a maximum light level and light levels lower than said maximum light level; and said threshold value being set such that the DC voltage exceeds said threshold value for asymmetry between the column discharges of each polarity at a light level lower than said maximum light level.
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Specification