Broadband Circuit Model of Common Mode Chokes for EMI pre-compliance assessment

Common mode chokes (CMCs) are used inside electro-magnetic interference (EMI) filter to suppress unwanted noise. Together with filter capacitors, CMCs can provide low-pass (LP) RLC filtering behavior. Two-winding CMCs are characterized by a common mode impedance ZC that is the impedance seen by common mode noise, and by a differential mode impedance ZD, which is dependent on the leakage inductance. Other impedances characterizing a CMC are the inter-winding impedance (ZIW), which is the impedance seen at the two terminals of the CMC, and the phase impedance (ZPH), that is the impedance seen from an input to output of the same winding. All these impedances can be assessed by measurement at the Vector Network Analyzer (VNA), or by means of an impedance analyzer. In this work we show how to construct a broadband model of the CMC, suitable for EMI pre-compliance assessment, by merging all the information of the four measurements related to the two-winding CMCs. This model might help hardware/power electronics engineers to perform preliminary simulations of the insertion losses of EMI filter, and to know in advance the minimum required falling slope necessary to achieve electromagnetic compatibility (EMC) pre-compliance.