PWM regulator with varying operating frequency for reduced EMI
AssigneeMicrel, Inc.
InventorJon R. Roman
Life of this patent
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Abstract
A switching regulator for reducing electromagnetic interference (EMI) includes a PWM controller which incorporates a varying frequency oscillator for controlling the operating frequency of the switching regulator. The varying frequency oscillator provides an oscillating signal having a continuously varying frequency about the center switching frequency of the switching regulator. The varying frequency oscillating signal causes the operating frequency of the switching regulator to vary, spreading out the EMI noise generated by the switching regulator and effectively reducing the peak energy of the EMI noise.
Claims33
A switching regulator for reducing electromagnetic interference (EMI) comprising:
- a PWM controller, said controller comprising:
- a varying frequency oscillator for controlling a switching frequency of at least one switching transistor coupled to said PWM controller, said oscillator providing an oscillating signal having a continuously varying frequency;
- and
- a control circuit for controlling a duty cycle of said at least one switching transistor, said control circuit coupled to receive said oscillating signal as a logic control signal from said varying frequency oscillator and generate a duty cycle control signal.
A switching regulator for reducing electromagnetic interference (EMI), comprising:
- a PWM controller, said controller comprising:
- a varying frequency oscillator for controlling a switching frequency of at least one switching transistor coupled to said PWM controller, said oscillator providing an oscillating signal having a continuously varying frequency, said varying frequency oscillator comprising:
- a voltage controlled oscillator receiving a voltage control input signal and generating said oscillating signal having said continuously varying frequency;
- wherein said voltage control input signal is the sum of a first voltage signal and a second voltage signal;
- said first voltage signal being selected to operate said voltage controlled oscillator at a center switching frequency of said at least one switching transistor;
- said second voltage signal being an oscillating voltage signal having a second frequency substantially lower than said center switching frequency, the amplitude of said second voltage signal being selected to define a frequency range within which said oscillating signal varies continuously about said center switching frequency.
A switching regulator for reducing electromagnetic interference (EMI), comprising:
- a PWM controller, said controller comprising:
- a varying frequency oscillator for controlling a switching frequency of at least one switching transistor coupled to said PWM controller, said oscillator providing an oscillating signal having a continuously varying frequency, said varying frequency oscillator comprising:
- a low frequency voltage controlled oscillator for providing a first oscillating signal having a first frequency, said first frequency being substantially lower than a center switching frequency of said at least one switching transistor;
- and
- a waveform generator providing a second oscillating signal operating at said center switching frequency of said at least one switching transistor, said first oscillating signal controlling said waveform generator to generate at an output terminal said oscillating signal having said continuously varying frequency.
A switching regulator for reducing electromagnetic interference (EMI), comprising:
- a PWM controller, said controller comprising:
- a varying frequency oscillator for controlling a switching frequency of at least one switching transistor coupled to said PWM controller, said oscillator providing an oscillating signal having a continuously varying frequency;
- and
- a second oscillator;
- wherein said varying frequency oscillator is coupled to a synchronization input terminal of said second oscillator, said second oscillator being synchronized to said oscillating signal of said varying frequency oscillator and generate an oscillating signal having a continuously varying frequency for controlling said switching frequency of said at least one switching transistor.
A method for reducing electromagnetic interference (EMI) in a switching regulator, said regulator comprising a PWM controller coupled to a varying frequency oscillator, said method comprising:
- generating an oscillating signal having a continuously varying frequency;
- generating a duty cycle control signal using said oscillating signal as a logic control signal;
- and
- controlling a duty cycle of at least one switching transistor at said continuously varying frequency to output a regulated voltage.
Dependencies are inferred from the claim text.