Control circuit having frequency modulation to reduce EMI of power converters
First Claim
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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Accused Products
Abstract
A control circuit having frequency modulation is used for reducing the EMI of a power converter. A switching circuit is couple to a feedback circuit to generate a switching signal for regulating an output of the power converter. A first oscillator is equipped to determine a switching frequency of the switching signal. A second oscillator is coupled to the first oscillator to modulate the switching frequency of the switching signal for reduce the EMI of the power converter. A programmable resistor is designed to attenuate the feedback signal of the feedback circuit. The resistance of the programmable resistor is controlled by the output of the second oscillator. Therefore, the output power and the output voltage can be kept constant when the switching frequency is modulated.
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Citations
10 Claims
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1. A control circuit having frequency modulation, comprising:
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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. - View Dependent Claims (2, 3, 4, 5)
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6. A control circuit having frequency modulation, comprising:
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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, coupled to said switching circuit to determine a switching frequency of said switching signal; a programmable capacitor, coupled to said first oscillator to modulate said switching frequency of said switching signal; a second oscillator, generating an oscillation signal, wherein an analog-to-digital converter 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 are coupled to control a capacitance of said programmable capacitor and a resistance of said programmable resistor. - View Dependent Claims (7, 8, 9, 10)
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Specification