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Dimming controller for a fluorescent lamp

  • US 5,504,398 A
  • Filed: 03/16/1995
  • Issued: 04/02/1996
  • Est. Priority Date: 06/10/1994
  • Status: Expired due to Fees
First Claim
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1. A control module for controlling the illumination intensity of a fluorescent lamp having cathodes, the control module adapted to be connected in series with the lamp cathodes and in series with a ballast and a source of AC power which is applied in alternating half-cycles of AC voltage and AC current, the control module comprising:

  • a current switch device which selectively conducts current through the cathodes when triggered into a conductive condition and which ceases conducting current when commutated into an non-conductive condition;

    a controller connected to trigger the switch device into the conductive condition and to commutate the switch device into the non-conductive condition, the controller triggering the switch device into the conductive condition at a predetermined extinguishing point within and prior to the end of each half-cycle of applied AC current, and the controller commutating the switch device into the non-conductive condition at a predetermined ignition point when the applied AC current reaches a predetermined level near the zero crossing point of each half-cycle of applied AC current;

    the predetermined level of the current at the ignition point and the commutation of the switch device to the non-conductive condition creating an ignition pulse of voltage from the ballast of a magnitude sufficient to ignite an illumination plasma between the cathodes;

    the conductive condition of the switch device at the extinguishing point extinguishes the illumination plasma; and

    the illumination intensity of the lamp is related to the time between the ignition point and the extinguishing point.

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