With the significant reduction in board space occupied by the smaller GaN transistors, topologies that require a greater number of active devices as a tradeoff for reduced passive size, the main barrier to higher power density, have become attractive. Switched capacitor multilevel converters are good examples of topologies that can effectively reduce or eliminate passive components. Two GaN-based proof-of-concept designs, based on the three-level buck converter, one for a low-voltage (LV) 48-V server application and the other as a candidate for a higher voltage (HV) 400-V power factor correction circuit application, are discussed in this article. As a result of using lower figure-of-merit devices, significant efficiency gains are observed for the LV and HV converters developed in this article compared to a two-level topology. Smaller passive size (mainly inductors) also provides a significant increase in power density for the LV converter. A startup scheme is discussed, which eliminates the need for extraneous control loops or high-voltage-rated devices for the top switch. Finally, the thermal benefit of the three-level converter is demonstrated when compared to a two-level system for the 48-V server application.

中文翻译：

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基于 GaN 的多电平开关电容器转换器的设计 - 优势和挑战

随着更小的 GaN 晶体管占用的电路板空间显着减少，需要更多有源器件作为降低无源尺寸（高功率密度的主要障碍）的权衡的拓扑变得有吸引力。开关电容器多电平转换器是可以有效减少或消除无源元件的拓扑的很好例子。两种基于 GaN 的概念验证设计，基于三级降压转换器，一种用于低电压 (LV) 48-V 服务器应用，另一种用作更高电压 (HV) 400-V 的候选功率因数校正电路的应用，将在本文中讨论。由于使用了较低品质因数的器件，与两电平拓扑相比，本文开发的 LV 和 HV 转换器具有显着的效率增益。较小的无源尺寸（主要是电感器）也显着提高了 LV 转换器的功率密度。讨论了一种启动方案，它消除了对顶部开关的额外控制回路或高压额定设备的需要。最后，与用于 48V 服务器应用的两电平系统相比，三电平转换器的散热优势得到了证明。