Enabling Resonant Commutated Pole in Parallel Power FET Bridge Legs

Abstract

To meet the requirements of higher current ratings and lower thermal impedances, paralleling power field-effect transistor (FET) discretes or modules is often a cost-effective or even an unavoidable solution. While paralleling FETs allows for a significant reduction in conduction loss, the switching loss is increased in hard-switching applications. This article proposes a generic soft-switching modulation scheme for parallel power FET bridge legs. Part of the paralleled FET legs is chosen as an auxiliary leg that is turned on prior to the remaining main legs. A resonant commutated pole (RCP) mode is then created, which enables the high-side FET of the auxiliary leg to achieve zero-current switching (ZCS) or quasi-ZCS and the remaining FETs to achieve zero-voltage switching. Thus, we can significantly reduce the switching loss that normally dominates the total power loss of high-frequency hard-switching converters particularly at partial and light loads. Experimental results from three parallel GaN high-electron-mobility transistor legs validate the effectiveness of this RCP-enabled solution in reducing switching losses and improving power conversion efficiencies. This article is accompanied by supplementary JIF and PDF files demonstrating the operational details of the RCP mode.