Semiconductor-based galvanic isolation

This paper presents the study on the semiconductor-based galvanic isolation. This solution delivers the differential-mode (DM) power via semiconductor power switches during their on states, while sustaining the common-mode (CM) voltage and blocking the CM leakage current with those switches during their off states. While it is impractical to implement this solution with Si devices, the latest SiC devices and the coming vertical GaN devices, however, provide unprecedented properties and thus can potentially enable the practical implementation. An isolated dc/dc converter based on the switched-capacitor circuit is studied as an example. The CM leakage current caused by the line input and the resulted touch current (TC) are quantified and compared to the limits in the safety standard IEC60950. To reduce the TC, low switch output capacitance and low converter switching frequency are needed. Then, discussions are presented on the TC reduction approaches and the design considerations to achieve high power density and high efficiency. A 400-V, 400-W prototype based on 1.7-kV SiC MOSFETs is built to demo the DM power delivery performance and showcase the CM leakage current problem. Further study on the CM leakage current elimination is needed to validate this solution.