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Phase controlled dimming system with active filter for preventing flickering and undesired intensity changes

  • US 6,380,692 B1
  • Filed: 09/18/2000
  • Issued: 04/30/2002
  • Est. Priority Date: 10/02/1997
  • Status: Expired due to Term
First Claim
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1. A load control system for reliably controlling the power applied to a load from an alternating current (AC) power source wherein the power may contain undesired noise, distortion, or frequency variation, the system comprising:

  • (a) a Bessel filter including an input to receive the power and an output to provide a filtered AC signal, the Bessel filter adapted to attenuate frequency components of the power that are substantially equal to third order harmonics and greater of an AC fundamental frequency;

    (b) a zero crossing detector coupled to the output of the Bessel filter to provide a zero crossing indication signal;

    (c) a microprocessor coupled to the output of the zero crossing detector, the microprocessor responsive to the zero crossing indication signal and to a signal indicative of a desired power level to provide a control signal; and

    (d) a controllably conductive device including a control lead coupled to an output of the microprocessor and responsive to the control signal, an input coupleable to the AC power source, and an output coupleable to the load.

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