Shielding-Based Common-Mode Noise Cancellation Techniques for Isolated DC-DC Converters

In isolated DC-DC converters, the transformer inter-winding capacitance is a critical path for propagating the common-mode (CM) noise. To block this propagation path and reduce the CM noise, a shielding layer is usually added between the primary and secondary windings. However, the displacement current between the shielding layer and the adjacent windings is generated and causes CM noise. In this chapter, two solutions are proposed to cancel the displacement current flowing between the shielding layer and the adjacent winding. The first solution is the shielding winding method, and the second solution is the combined shielding and balancing-winding method. In addition to the inter-winding capacitance, the parasitic capacitance between the high dv/dt nodes in the primary circuit and the protective earth (PE) is another path for propagating the CM noise. In order to cancel the CM noise completely, the shielding winding method is combined with symmetry circuit. Furthermore, the combined shielding and balancing-winding method is combined with passive cancellation, resulting in the hybrid passive cancellation (HPC) method. Finally, the shielding winding method, the combined shielding and balancing-winding method, and the HPC method are verified by the experimental results.