Common-Mode Noise Modeling and Reduction for 1-MHz eGaN Multioutput DC–DC Converters

Enhancement-mode gallium nitride (eGaN) high-electron-mobility transistors (HEMTs) are promising to increase the switching frequency into multimegahertz for the high power density. However, it is a serious challenge to identify the equivalent lumped capacitances of megahertz multiwinding planar transformers for common-mode (CM) noise analysis to optimize the electromagnetic interference filters. The couple turn with its one-capacitor model is proposed to quantify the total CM noise current via the high-frequency transformer. With the modeled total CM noise current, the equivalent lumped interwinding capacitance model of the transformer can be derived conveniently and accurately. A complete CM noise path model is built for a GaN-based active clamp forward with a self-driven synchronous rectification multioutput converter. Then, a CM noise cancelation capacitance is applied and optimized to generate a reverse extraction current to cancel the CM noise current. Compared with other methods, the proposed modeling technique can build the equivalent lumped interwinding capacitance model of the multiwinding planar transformer in the printed circuit board layout stage before it is fabricated physically. The proposed model is verified by the experimental results with a 1-MHz GaN prototype with 100-V input, 5-V/6-A, and ±12-V/ 0.83-A outputs. The CM noise spectrum is well predicted. The CM noise is reduced by around 15 dB (a reduction of 12.6%) below 9 MHz.