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Characterization, Evaluation and Design of Noise Separator for Conducted EMI Diagnosis

EMI diagnosis and EMI filter design need accurate DM and CM noise separation and measurement. Noise separator is a powerful tool to separate and measure EMI noise. Since all EMI standards are based on the noise voltage drop on 50 Ohm resistance, the noise separator must have 50 Ohm input impedances under any conditions. Furthermore, the noise separator should accurately finish the calculation to separate DM and CM noise. The noise rejection ratio should also be good enough to reject the unwanted noise mode. A noise separator is proposed in CPES using transmission line transformer, which can cancel the effects of winding capacitance and leakage inductance of the windings. 50 Ohm input impedance is also guaranteed under any conditions. The rejection ratio is pretty good to efficiently prevent the interference of unwanted EMI mode in the measurement. The noise separator integrates both CM and DM separators, so it is easy to measure both noise at the same time without switching connectors.

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