Single stage, high power factor, gas discharge lamp ballast
First Claim
1. A single stage, high power factor, gas discharge lamp ballast comprisingmeans for full-wave rectifying low frequency ac line voltage, said rectifying means including a low-pass filter,a single switching power conversion stage connected to said ac voltage rectifying means for convening rectified sine-wave line voltage to a square-wave voltage at a constant high switching frequency, fs, anda resonant matching network for convening said square-wave voltage source into an ac sine-wave current source at said high switching frequency needed to drive said gas discharge lamp,said single power conversion stage comprising, an input inductor, and an energy transfer capacitor connected in series between said rectifying means and said resonant matching network, and switching means for alternately connecting a junction between said input inductor and energy transfer capacitor and a junction between said energy transfer capacitor and said resonant matching network to a return current path, anda fast recovery semiconductor diode inserted in series with said input inductor chosen to have an inductance L1 to be less than a critical value of inductance, Lcrit, for a given switching period Ts at said constant high switching frequency, fs, to force discontinuous inductor current mode of operation of said switching power conversion stage,said switching means comprising first and second current bidirectional switches driven out of phase such that, when said first current bidirectional switch is on, said second bidirectional switch is off, and vice versa, thus producing said square-wave high frequency voltage,said resonant matching network comprising means for converting said square-wave voltage source into sine-wave ac current source required by said gas discharge lamp, and for blocking any dc component of said square-wave voltage from reaching said gas discharge lamp, andswitching control means for alternately turning on said first and second current bidirectional switches at a fixed switching frequency and a constant duty ratio in a mode of control selected from open-loop and closed-loop control of said high frequency ac current through said gas discharge lamp,whereby said input fast-recovery semiconductor diode, in conjunction with said input inductor chosen to be less than a predetermined critical inductance, forces said single stage power converter into a discontinuous inductor current mode of operation despite operation of said first and second switching means as bidirectional current switches, such that average input inductor current from said rectifying means filtered by said low-pass filter very closely follows instantaneous line voltage for near unity input power factor operation while operating at a fixed switching frequency and a constant duty ratio, and providing ac current lamp ballast.
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Accused Products
Abstract
A gas discharge lamp ballast provides near unity power factor simultaneously with high-frequency lamp ballasting in a single switching power conversion stage resulting in efficiency improvements, reduction in size and weight and reduced component count and cost. The single conversion stage comprises a fast-recovery diode connecting in series the input inductor, energy transfer capacitor and the resonant matching network, and switching means alternately connecting the first junction between the input inductor and energy transfer capacitor, or the second junction between the matching network and the other side of said capacitor to the return current path. The switching means comprises two current bidirectional switches driven out of phase, thus producing a square-wave high frequency voltage source, which is in turn converted by the resonant matching network into a sine-wave ac current source required by the gas discharge lamp. The fast-recovery input diode in conjunction with the input inductance chosen to be less than the critical inductance value forces the input inductor current into a new discontinuous inductor current mode (DICM). The average input inductor current is shown to closely follow the rectified line voltage when the ballast is operated at the constant duty ratio and at the constant switching frequency either open-loop or with the slow feedback loop of conventional PWM control. Zero voltage switching for the two current bidirectional switches is achieved by introducing two transition intervals during which both switches are OFF and utilizing the negative value of the lagging current of the matching network above resonance.
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Citations
26 Claims
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1. A single stage, high power factor, gas discharge lamp ballast comprising
means for full-wave rectifying low frequency ac line voltage, said rectifying means including a low-pass filter, a single switching power conversion stage connected to said ac voltage rectifying means for convening rectified sine-wave line voltage to a square-wave voltage at a constant high switching frequency, fs, and a resonant matching network for convening said square-wave voltage source into an ac sine-wave current source at said high switching frequency needed to drive said gas discharge lamp, said single power conversion stage comprising, an input inductor, and an energy transfer capacitor connected in series between said rectifying means and said resonant matching network, and switching means for alternately connecting a junction between said input inductor and energy transfer capacitor and a junction between said energy transfer capacitor and said resonant matching network to a return current path, and a fast recovery semiconductor diode inserted in series with said input inductor chosen to have an inductance L1 to be less than a critical value of inductance, Lcrit, for a given switching period Ts at said constant high switching frequency, fs, to force discontinuous inductor current mode of operation of said switching power conversion stage, said switching means comprising first and second current bidirectional switches driven out of phase such that, when said first current bidirectional switch is on, said second bidirectional switch is off, and vice versa, thus producing said square-wave high frequency voltage, said resonant matching network comprising means for converting said square-wave voltage source into sine-wave ac current source required by said gas discharge lamp, and for blocking any dc component of said square-wave voltage from reaching said gas discharge lamp, and switching control means for alternately turning on said first and second current bidirectional switches at a fixed switching frequency and a constant duty ratio in a mode of control selected from open-loop and closed-loop control of said high frequency ac current through said gas discharge lamp, whereby said input fast-recovery semiconductor diode, in conjunction with said input inductor chosen to be less than a predetermined critical inductance, forces said single stage power converter into a discontinuous inductor current mode of operation despite operation of said first and second switching means as bidirectional current switches, such that average input inductor current from said rectifying means filtered by said low-pass filter very closely follows instantaneous line voltage for near unity input power factor operation while operating at a fixed switching frequency and a constant duty ratio, and providing ac current lamp ballast.
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4. A single stage, high power factor, gas discharge lamp ballast between an ac power line and a gas discharge lamp comprising
means for full-wave rectifying low frequency ac line voltage, said rectifying means including a low-pass filter, a single switching power conversion stage connected to said ac voltage rectifying means for convening rectified sine-wave line voltage to a square-wave voltage at a constant high switching frequency, fs, and a resonant matching network for converting said square-wave voltage source into an ac sine-wave current source at said high switching frequency needed to drive said gas discharge lamp, said single power conversion stage comprising an input inductor and an energy transfer capacitor connected in series between said rectifying means and said resonant matching network, and switching means for alternately connecting a junction between said input inductor and energy transfer capacitor and a junction between said energy transfer capacitor and said resonant matching network to a return current path, and fast recovery semiconductor diode means between said ac power line and said input inductor chosen to have an inductance L1 to be less than a critical value of inductance, Lcrit, for a given switching period Ts at said constant high switching frequency, fs, to force discontinuous inductor current mode of operation of said switching power conversion stage, said switching means comprising first and second current bidirectional switches driven out of phase such that, when said first current bidirectional switch is on, said second bidirectional switch is off, and vice versa, thus producing said square-wave high frequency voltage, said resonant matching network comprising means for converting said square-wave voltage source into sine-wave ac current source required by said gas discharge lamp, and for blocking any dc component of said square-wave voltage from reaching said gas discharge lamp, and switching control means for alternately turning on said first and second current bidirectional switches at a fixed switching frequency and a constant duty ratio in a mode of control selected from open-loop and closed-loop control of said ac current through said gas discharge lamp, whereby said fast recovery semiconductor means, in conjunction with said input inductor chosen to be less than a predetermined critical inductance, forces said single stage power converter into a discontinuous inductor current mode of operation despite operation of said first and second switching means as bidirectional current switches, such that average input inductor current from said rectifying means filtered by said low-pass filter very closely follows instantaneous line voltage for near unity power input factor operation while operating at a fixed switching frequency and a constant duty ratio, and providing ac current lamp ballast.
Specification