METHODS AND APPARATUS FOR A HIGH POWER FACTOR BALLAST HAVING HIGH EFFICIENCY DURING NORMAL OPERATION AND DURING DIMMING
First Claim
Patent Images
1. A ballast circuit, comprising:
- a rectifier connected to a first node and a second node, the rectifier configured to provide an output of unfiltered DC voltage varying at twice a line frequency, said DC voltage being rectified from an AC voltage power source alternating at said line frequency, wherein the first node is connected to a first terminal of a bypass capacitor and the second node is connected to a second terminal of the bypass capacitor, said bypass capacitor storing energy at a first frequency that exceeds the line frequency, wherein said bypass capacitor presents a high impedance to the unfiltered DC voltage at the line frequency;
a first switch connected to the first node operable to selectively couple the first node to a resonant circuit, the resonant circuit having a resonant frequency and configured to be connected to a light source, wherein the resonant circuit stores energy during a first portion of a cycle of the first frequency;
a second switch operable to selectively couple the resonant circuit to the second node, the second switch causing all or some of the energy stored in the resonant circuit to be recirculated into the resonant circuit during a second portion of the cycle of the first frequency.
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Accused Products
Abstract
Methods and apparatus for powering a ballast that is dimmable and has a high power factor. The ballast circuit includes a rectifier, bypass capacitor, a driver circuit, and a resonant circuit that are configured to actuate a light source, such as a fluorescent lamp. Specifically, the bypass capacitor stores energy to produce a high frequency current which is introduced into the resonant circuit to continually recycle energy in the resonant circuit, resulting in a circuit with a high power factor. Further, because the current flowing into the resonant circuit is substantially sinusoidal, the circuit generally has an ideal crest factor, thereby increasing the lifespan of the light source.
35 Citations
28 Claims
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1. A ballast circuit, comprising:
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a rectifier connected to a first node and a second node, the rectifier configured to provide an output of unfiltered DC voltage varying at twice a line frequency, said DC voltage being rectified from an AC voltage power source alternating at said line frequency, wherein the first node is connected to a first terminal of a bypass capacitor and the second node is connected to a second terminal of the bypass capacitor, said bypass capacitor storing energy at a first frequency that exceeds the line frequency, wherein said bypass capacitor presents a high impedance to the unfiltered DC voltage at the line frequency; a first switch connected to the first node operable to selectively couple the first node to a resonant circuit, the resonant circuit having a resonant frequency and configured to be connected to a light source, wherein the resonant circuit stores energy during a first portion of a cycle of the first frequency; a second switch operable to selectively couple the resonant circuit to the second node, the second switch causing all or some of the energy stored in the resonant circuit to be recirculated into the resonant circuit during a second portion of the cycle of the first frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of powering a ballast circuit, comprising:
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charging energy in a non-electrolytic bypass capacitor connected to the outputs of a full wave bridge rectifier wherein the value of the bypass capacitor is such that the bypass capacitor is discharged every half cycle at a line frequency; storing energy in the bypass capacitor to subsequently produce a high frequency current from the bypass capacitor, the bypass capacitor connected to a first node and a second node; selectively coupling the bypass capacitor to a resonant circuit via the first node for a first time period, wherein coupling the resonant circuit to the first node results in a voltage at a light source, wherein said voltage at the light source is the result of the combination of a first current from an output of the full wave bridge rectifier at the line frequency, the high frequency current from the bypass capacitor, and a second current present in the resonant circuit; and selectively coupling the resonant circuit to the second node for a second time period, wherein coupling the second node generates a negative voltage in the resonant circuit at the light source and allows energy from the full wave bridge rectifier to be stored in the bypass capacitor. - View Dependent Claims (17, 18, 19)
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20. A ballast circuit comprising:
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a full wave bridge configured to receive AC voltage at a line frequency, said full wave bridge having a first node and a second node, said full wave bridge configured to provide an unfiltered DC voltage having a rectified AC voltage waveform at said first node, said full wave bridge configured to provide a first current at said line frequency; a bypass capacitor comprising a non-electrolytic capacitor having a value of less than 3 μ
F, said bypass capacitor having a first terminal connected to said first node and second terminal connected to said second node, said bypass capacitor configured to provide a second current at a high frequency;a driver circuit configured to periodically generate a first activation signal and a second activation signal; a first solid state switch connected to receive said first activation signal, said first solid state switch having a first terminal connected to said first node and a second terminal connected to a third node, said first solid state switch configured to connect said first node to said third node when activated by said first activation signal thereby providing said first current and said second current to said third node; a second solid state switch connected to receive said second activation signal, said second solid state switch having a first terminal connected to said third node and a second terminal connected to said second node; and a resonant circuit comprising a first capacitor, an inductor, a second capacitor, and a third capacitor, wherein; the first capacitor has a first terminal is connected to said third node, said first capacitor having a value of less than 0.2 μ
F;the inductor has a first terminal connected to a second terminal of said first capacitor and has a second terminal connected to a first terminal of the second capacitor, the second capacitor has a second terminal connected to the second node, said second terminal of said inductor is configured to be connected to first terminal of a third capacitor via a first filament terminal of a first filament of a gas-discharge lamp, said third capacitor having a second terminal is configured to be connected to a second filament terminal of the first filament of the gas-discharge lamp, wherein said third capacitor is configured to be connected to a first filament terminal of a second filament of the gas discharge lamp and said second node is configured to be connected to a second filament terminal of the second filament of the gas-discharge lamp, and wherein, said inductor is sized so as to not be saturated during a peak current flowing through said inductor, said peak current comprising the first current and the second current at the time when the output of the rectifier is at its highest output voltage. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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28. A method of operating a ballast to generate light from a fluorescent bulb comprising the steps of:
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selectively switching at a switching frequency by a first solid state switch a rectified AC voltage at a line frequency thereby providing a plurality of switched DC voltages to a resonant circuit; producing a plurality of alternating bulb voltages by said resonant circuit to said fluorescent bulb wherein; a first portion of said plurality of alternating bulb voltages increase in magnitude of voltage for a first time period during which said fluorescent bulb is not ionized, a second portion of said plurality of alternating bulb voltages remain constant in magnitude of voltage for a second time period due to ionization occurring in said fluorescent bulb, a third portion of said plurality of alternating bulb voltages decrease in magnitude of voltage for a third time period during which said fluorescent bulb is not ionized, and wherein said first time period, said second time period, and said third time period occur during a half cycle of said line frequency.
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Specification