Study of two switch forward converter using multi-winding transformer

This paper addresses the common mode (CM) electromagnetic noise issues in two switch forward converter. The two switch forward converter has low common mode noise compared to other topologies because its symmetric primary side circuit has two out of phase dv/dts that cancel each other. However parasitic capacitances of the circuit significantly affect the symmetry and degrade the noise reduction. Additionally, the secondary side circuit of the converter is not symmetric and still contributes to the common mode. In this work, the parasitic capacitances of the converter are to be modeled first. Different transformer structure and their parasitic capacitances are characterized. A general balance technique is introduced to further reduce the CM noise of the converter. For multi-winding transformer structure, balance can be achieved with proper arrangement of the winding terminals and control the parasitic capacitances to minimize the CM noise of the converter. Simulation results are shown to verify this concept.