EMI Reduction by Extended Spread Spectrum in Switching Converter

摘要

This paper proposes new EMI reduction method by extended spread spectrum using the PLL circuit with pseudo analog noise which is produced from new M-sequence circuit. The PLL circuit makes the reference clock modified with non-periodic analog noise which is supplied from new 3-bit M-sequence circuit. New pseudo analog noise is produced by inversing and/or exchanging the 3-bit. Using this modified clock from the PLL circuit for the saw-tooth signal in the switching converter, the spectrum of the PWM pulses is widely spread and the peak levels of the spectrums of the fundamental frequency and the harmonic frequencies are much reduced.