PWM capacitor control

  • US 10,063,104 B2
  • Filed: 02/08/2017
  • Issued: 08/28/2018
  • Est. Priority Date: 02/08/2016
  • Status: Active Grant
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First Claim
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1. A variable capacitance device comprising:

  • a capacitor;

    a first transistor comprising a first-transistor source terminal, a first-transistor drain terminal, and a first-transistor gate terminal, the first-transistor drain terminal electrically connected to a first terminal of the capacitor;

    a second transistor comprising a second-transistor source terminal, a second-transistor drain terminal, and a second-transistor gate terminal, the second-transistor drain terminal electrically connected to a second terminal of the capacitor, and the second-transistor source terminal electrically connected to the first-transistor source terminal; and

    control circuitry coupled to the first-transistor gate terminal and the second-transistor gate terminal,wherein the control circuitry is configured to adjust an effective capacitance of the capacitor by performing operations comprising;

    detecting a first zero-crossing of an input current at a first time;

    after a first delay period from the first time, switching off the first transistor, wherein a length of the first delay period is controlled by an input value;

    detecting a second zero-crossing of the input current at a second time, after the first time;

    measuring an elapsed time between switching off the first transistor and detecting the second zero-crossing;

    setting a counter based on the elapsed time; and

    after a second delay period based on the counter, switching on the first transistor.

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