Series connection type common-mode current reduction circuit

In order to reduce EMI noise, a novel common-mode current reduction circuit connected in series with the main circuit is proposed. The circuit consists of only passive components, such as the asymmetrical-snubber, a common-mode transformer, and some R, L, and C components. Hence, the circuit is expected to reduce EMI noise, especially in the high-frequency region. The optimum parameter conditions at which the circuit most effectively reduces EMI noise are investigated. Based on the root locus method, the optimum parameter conditions at which the leakage current has minimum amplitude with no oscillatory component is discussed. The experimental results agree well with the theoretical calculations and prove that the proposed method is useful for reducing EMI noise especially conducted EMI noise.