This paper presents the benefits and drawbacks of replacing the traditional Si Mosfets transistors with enhancement mode GaN transistors in a Half-Bridge Zero Voltage and Zero Current Switching Power Switching (ZVZCPS) converter. This type of converters is usually used as Electronic Power Converters (EPC) for telecommunication satellites travelling-wave tube amplifiers (TWTAs). In this study, firstly the converter is theoretically analysed, obtaining its operation, losses and efficiency equations. From these equations, optimizations maps based on the main system parameters are obtained. These optimization maps are the key to quantify the potential benefits of GaN transistors in this type of converters. Theoretical results show that using GaN transistors, the frequency of the converter can be pushed from 125kHz to 830kHz without sacrificing the converter efficiency. This frequency increase is directly related to reduction on the EPC size and weight. To validate the theoretical results, a 150W prototype was built and its performance measured. Experimental results show an unexpected operation at high frequencies, mainly due to the influence of the transformer parasitic capacitance and the rectifiers diodes reverse recovery effect. Finally, it can be concluded that the parasitic capacitance of the converter and the diodes recovery time are, in practice, critical parameters to increase the switching frequency keeping the ZVZCPS.
The paper focuses on a new generation of power modules, trying to optimize the tradeoff between thermal and EMI managements. At the same time, the packaging approach is considered in order to simplify the implementation of the power dies while improving the reliability of the structure. The approach considers the hybrid integration of the power dies, one on top of the other into a 3D Chip On Chip configuration. Thanks to this structure, the power dies can be directly inserted within electrical plates, the whole structure emulating a busbar like power module. The paper presents the characteristics and the benefits of the approach. Then, it focuses on the practical characterization of two prototypes: a buck converter structure and a full bridge, single phase diode rectifier. Both of them are based on double sided thermal cooling and electro-thermal contacts are obtained by pressure. The prototypes exhibit great performances while offering really reduced parasitic and EMI coupling.
GaN transistors can be used instead of Si MOSFET, because they improve static and dynamic performances. Moreover, low power DC-DC converters are often not very efficient, so GaN represents a good solution to improve efficiency. This article presents a comparison between Si MOSFET and GaN HEMT performances by using them in a high frequency isolated DC-DC converter. The structure and his control are described, and the maximum efficiency is higher than 94%. After having highlighted critical points for efficiency, a way to improve working conditions of GaN transistors is investigated. The converter is based on EPC GaN components.
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