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Control circuit having frequency modulation to reduce EMI of power converters

  • US 7,489,529 B2
  • Filed: 11/08/2005
  • Issued: 02/10/2009
  • Est. Priority Date: 11/08/2005
  • Status: Active Grant
First Claim
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1. A control circuit having frequency modulation, comprising:

  • a switching circuit, coupled to a feedback circuit to generate a switching signal for regulating an output of a power converter;

    wherein said feedback circuit receives said output of said power converter for producing a feedback signal to control said switching signal;

    a first oscillator, generating a clock signal to said switching circuit to determine a switching frequency of said switching signal;

    a programmable capacitor, connected to said first oscillator for modulating a frequency of said clock signal;

    a second oscillator, generating an oscillation signal, wherein an encoding circuit generates digital signals in response to said oscillation signal; and

    a programmable resistor, coupled to said feedback circuit for attenuating said feedback signal;

    wherein said digital signals control said programmable capacitor for modulating said switching frequency of said switching signal; and

    said digital signals control said programmable resistor for programming an attenuation rate of said feedback signal.

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