Selectable notch frequencies of EMI spread spectrum using pulse modulation in switching converter

This paper proposes a novel EMI spread spectrum technique to enable to set notch frequencies using pulse modulation in switching converters. The notches appear at the frequencies obtained from empirically derived equations with the proposed spread spectrum technique using the pulse coding methods, the PWM (Pulse Width Modulation) coding or the PCM (Pulse Code Modulation) coding. This technique would be useful for the communication equipment which receives standard radio waves, without being affected by noise from the switching converters. In our proposed technique, the notch frequencies in the spread spectrum depend on the pulse coding method. We have investigated this technique to apply to the switching converters and found that there is good relationship agreement between the notch frequencies and the empirical equations. The notch frequency in the PWM coding is equal to the equation F=k/(W
_M
-Wo). In the PCM coding, that is equal to the equation F=k/(T
_M
-To).