Discussions on the semiconductor-based galvanic isolation

This paper presents the discussions on a semiconductor-based solution for galvanic isolation. It is a switched-capacitor (SC) isolated dc/dc converter based on the SC isolation cell structure, which aims to utilize the semiconductor switches to sustain isolation voltage and block common-mode (CM) leakage current. The converter delivers an active power with ZCS operation. The circuit structure and operation principle are introduced. To achieve high efficiency, the converter requires high voltage rating, low output capacitance, and low on-resistance of the switches, which makes the SiC devices the best choice, as shown in a comparison between the state-of-the-art Si and SiC devices. To validate the galvanic isolation, the isolation voltage and touch current (TC) must be evaluated according to the industrial safety standards such as IEC60950-1. Series connection of the SC isolation cells contributes to higher isolation voltage of the. It is also expected to provide smaller equivalent series capacitance which has higher impedance to block the line-frequency CM leakage current. However, study shows that the charging transients of the switch output capacitance results in a CM leakage current. This issue is verified by the test results from a prototype made of 2 SC isolation cells in series. This CM leakage current remains as a challenge for this isolation solution.