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Ballast circuit with lamp cathode protection and ballast protection

  • US 6,653,800 B2
  • Filed: 11/06/2001
  • Issued: 11/25/2003
  • Est. Priority Date: 11/06/2001
  • Status: Expired due to Fees
First Claim
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1. A ballast circuit for driving a fluorescent lamp, comprising:

  • a self-oscillating circuit for producing a periodic a.c. signal having a first cycle and a second cycle; and

    a series resonant circuit operationally coupled to the self-oscillating circuit and adapted for operationally coupling with a first and second cathode of the lamp, the resonant circuit further including;

    a resonant inductor operationally coupled to the self-oscillating circuit, a resonant capacitor, a first diode with an anode lead and a cathode lead operationally coupled between the resonant inductor and resonant capacitor and adapted for operationally coupling across the first cathode of the lamp, and a second diode with an anode lead and a cathode lead operationally coupled between the resonant capacitor and the self-oscillating circuit, wherein the leads of the second diode are in an opposite orientation from the leads of the first diode with respect to the series resonant circuit, and the second diode being adapted for operationally coupling across the second cathode of the lamp;

    wherein at least one of the first and second diodes substantially blocks resonant circuit current from flowing during a predetermined first or second cycle of the self-oscillating circuit when the lamp is coupled to the ballast circuit and one or more of the first and second cathodes of the lamp has failed.

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