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Liquid crystal display system with lamp feedback

  • US 7,394,209 B2
  • Filed: 06/16/2004
  • Issued: 07/01/2008
  • Est. Priority Date: 02/11/2004
  • Status: Expired due to Fees
First Claim
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1. A liquid crystal display system comprising:

  • a liquid crystal display panel;

    a cold cathode fluorescent lamp for illuminating said liquid crystal display panel;

    a secondary transformer winding coupled to said cold cathode fluorescent lamp for providing current to said cold cathode fluorescent lamp;

    a primary transformer winding coupled to said secondary transformer winding for providing magnetic flux to said secondary transformer winding;

    a first switch coupled to said primary transformer winding for allowing a forward-biased DC current to pass through said primary transformer winding;

    a second switch coupled to said primary transformer winding for allowing a reverse-biased DC current to pass through said primary transformer winding;

    a sense resistor electrically coupled to said cold cathode fluorescent lamp and electrically coupled to ground for providing a voltage feedback signal representing current through said cold cathode fluorescent lamp;

    a feedback control loop circuit coupled to said cold cathode fluorescent lamp and electrically coupled to said sense resistor for receiving a said voltage feedback signal and controlling power supplied to said cold cathode fluorescent lamp when said voltage feedback signal is above a predetermined threshold; and

    an input selector pin coupled to said feedback control loop circuit for selecting between linear mode power control and pulse width modulation power control.

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