A Novel Transformer for Forward Converter EMI Improvement

Abstract

This paper analyzes the common-mode interference conducted by the planar transformer in an isolated DC-DC converter and proposes a scheme for common-mode interference suppression. The scheme integrates the compensation capacitor for suppressing the common-mode current into the planar transformer, and its working principle is briefly explained in the paper. In addition, the scheme is verified by an active clamped forward converter. The application of this scheme in forward converter requires that the filter inductor on the secondary side be placed between the source of MOSFETs and the ground of secondary side, and it is necessary to add an inductor at the feedback terminal of the compensation loop, which needs to be coupled with the secondary filter inductor to ensure the normal driving of the MOSFETs. Finally, we made a prototype with an input voltage of 28 V and an output voltage of 5 V, and tested the common-mode interference of the prototype when using different planar transformers, which verified the feasibility of the scheme proposed in this paper.