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AC LED dimmer and dimming method thereby

  • US 8,901,841 B2
  • Filed: 12/03/2012
  • Issued: 12/02/2014
  • Est. Priority Date: 09/05/2008
  • Status: Active Grant
First Claim
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1. A method of dimming an alternating current (AC) light-emitting diode (LED) utilizing a pulse width modulation generator, comprising:

  • converting an AC input voltage having a first frequency to a first direct current (DC) voltage having a constant value;

    generating a square-wave voltage having a second frequency higher than the first frequency using the first DC voltage, the square-wave voltage having a first positive voltage value for a first half-cycle and a negative voltage value for a second half-cycle;

    full-wave rectifying the square-wave voltage to generate a second DC voltage having a second voltage value;

    half-wave rectifying the square-wave to generate a pulse enable signal having the second frequency, the pulse enable signal having the second voltage value for a first half-cycle and a zero voltage value for a second half-cycle;

    generating a pulse width modulation signal having the second frequency using the second DC voltage and the pulse enable signal, the pulse modulation signal having a duty ratio varying according to a dimming level; and

    driving the LED by using a switch to selectively apply the AC input voltage to the LED according to the duty ratio of the pulse width modulation signal.

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