Modeling of the Common-Mode Noise for Isolated DC-DC Converters

For isolated DC-DC converters, there are two propagation paths for the common-mode (CM) noise. One is the parasitic capacitance between the high dv/dt nodes in the primary circuit and the protective earth (PE), and the other is the transformer inter-winding capacitance. For the convenience of analyzing the CM noise, the transformer inter-winding capacitances are usually converted into lumped capacitances. In this chapter, a generalized lumped capacitance model is presented, which is applicable for a general converter using the transformer with a general winding structure. Then, the CM noise models for basic isolated DC-DC converters are derived, and the characteristics of internal impedance and equivalent noise source (ENS) of the CM noise model are revealed. Finally, the lumped capacitance model and the CM noise model are verified by the experimental results.