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EBL having a feedback circuit and a method for ensuring low temperature lamp operation at low dimming levels

  • US 5,850,127 A
  • Filed: 05/10/1996
  • Issued: 12/15/1998
  • Est. Priority Date: 05/10/1996
  • Status: Expired due to Fees
First Claim
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1. A dimmable ballast lamp, including:

  • a lamp;

    a ballast circuit including an inverter coupled to and for powering the lamp and having in response to a dimming control signal at least one adjustable operational characteristic selected from the group of duty cycle and switching frequency;

    a dimming circuit coupled to the inverter for producing said dimming control signal in response to a control input signal which is based when avoiding a shutoff condition of said lamp on a first precontrol input signal being raised by addition thereto of a second precontrol input signal;

    a dimming control interface for producing said first precontrol input signal based on a selected brightness level; and

    a feedback control circuit for detecting the shutoff condition of said lamp and for producing said second precontrol input signal in response to detection of said shutoff condition, said dimming circuit being responsive to said first precontrol input signal and to said second precontrol input signal for adjusting the brightness of said lamp to a higher brightness level than said selected brightness level independent of the ballast circuit impedance to thereby avoid the shutoff condition of said lamp.

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