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Single stage, high power factor, gas discharge lamp ballast

  • US 5,416,387 A
  • Filed: 11/24/1993
  • Issued: 05/16/1995
  • Est. Priority Date: 11/24/1993
  • Status: Expired due to Term
First Claim
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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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