The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

In this paper, we present a comprehensive reviewand discussion of the state-of-the-art device technology and application development of GaN-on-Si power electronics. Several device technologies for realizing normally off operation that is highly desirable for power switching applications are presented. In addition, the examples of circuit applications that can greatly benefit from the superior performance of GaN power devices are demonstrated. Comparisonwith other competingpower device technology, such as Si superjunction-MOSFET and SiC MOSFET, is also presented and analyzed. Critical issues for commercialization of GaN-on-Si power devices are discussed with regard to cost, reliability, and ease of use.

GaN-on-Si Power Technology: Devices and Applications

Gallium nitride (GaN) power devices are an emerging technology that have only recently become available commercially. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This paper reviews the characteristics and commercial status of both vertical and lateral GaN power devices, providing the background necessary to understand the significance of these recent developments. In addition, the challenges encountered in GaN-based converter design are considered, such as the consequences of faster switching on gate driver design and board layout. Other issues include the unique reverse conduction behavior, dynamic $R_{\mathrm {{ds}},\mathrm {{on}}}$ , breakdown mechanisms, thermal design, device availability, and reliability qualification. This review will help prepare the reader to effectively design GaN-based converters, as these devices become increasingly available on a commercial scale.

Review of Commercial GaN Power Devices and GaN-Based Converter Design Challenges

This timely second edition has been substantially expanded to keep students and practicing power conversion engineers ahead of the learning curve in GaN technology advancements. Acknowledging that GaN transistors are not one-to-one replacements for the current MOSFET technology, this book serves as a practical guide for understanding basic GaN transistor construction, characteristics, and applications. Included are discussions on the fundamental physics of these power semiconductors, layout and other circuit design considerations, as well as specific application examples demonstrating design techniques when employing GaN devices.

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GaN Transistors for Efficient Power Conversion

Gallium nitride high electron mobility transistor (GaN HEMT) has matured dramatically over the last few years. A progressively larger number of GaN devices have been manufactured for in field applications ranging from low power voltage regulators to high power infrastructure base-stations. Compared to the state-of-the-art silicon MOSFET, GaN HEMT has a much better figure of merit and shows potential for high-frequency applications. The first generation of 600 V GaN HEMT is intrinsically normally on device. To easily apply normally on GaN HEMT in circuit design, a low-voltage silicon MOSFET is in series to drive the GaN HEMT, which is well known as cascode structure. This paper studies the characteristics and operation principles of a 600 V cascode GaN HEMT. Evaluations of the cascode GaN HEMT performance based on buck converter at hard-switching and soft-switching conditions are presented in detail. Experimental results prove that the cascode GaN HEMT is superior to the silicon MOSFET, but it still needs soft-switching in high-frequency operation due to considerable package and layout parasitic inductors and capacitors. The cascode GaN HEMT is then applied to a 1 MHz 300 W 400 V/12 V LLC converter. A comparison of experimental results with a state-of-the-art silicon MOSFET is provided to validate the advantages of the GaN HEMT.

Evaluation and Application of 600 V GaN HEMT in Cascode Structure

The introduction of enhancement-mode gallium-nitride-based power devices such as the eGaN FET offers the potential to achieve higher efficiencies and higher switching frequencies than possible with silicon MOSFETs. With the improvements in switching performance and low parasitic packaging provided by eGaN FETs, the printed circuit board (PCB) layout becomes critical to converter performance. This paper will study the effect of PCB layout parasitic inductance on efficiency and peak device voltage stress for an eGaN FET-based point of load (POL) converter operating at a switching frequency of 1 MHz, an input voltage range of 12-28 V, an output voltage of 1.2 V, and an output current up to 20 A. This paper will also compare the parasitic inductances of conventional PCB layouts and propose an improved PCB design, providing a 40% decrease in parasitic inductance over the best conventional PCB design.

Understanding the Effect of PCB Layout on Circuit Performance in a High-Frequency Gallium-Nitride-Based Point of Load Converter

The introduction of enhancement mode gallium nitride based power devices such as the eGaN®FET offers the potential to achieve higher efficiencies and higher switching frequencies than possible with Silicon MOSFETs. With the improvements in switching performance and low parasitic packaging provided by eGaN FETs, the PCB layout becomes critical to converter performance. This paper will study the effect of PCB layout parasitic inductance on efficiency and peak device voltage stress for an eGaN FET based point of load (POL) converter operating at a switching frequency of 1 MHz, an input voltage range of 12-28 V, an output voltage of 1.2 V, and an output current up to 20 A. This work will also compare the parasitic inductances of conventional PCB layouts and propose an improved PCB design providing a 40% decrease in parasitic inductance over the best conventional PCB design.

Understanding the effect of PCB layout on circuit performance in a high frequency gallium nitride based point of load converter

The demand for the future power supplies that can achieve higher output currents, smaller sizes, and higher efficiencies cannot be satisfied with the conventional technologies. There are limitations in the switch performance, packaging parasitics, layout parasitics, and thermal management that must be addressed to push for higher frequencies and improved power density. To address these limitations, the utilization of Gallium-Nitride (GaN) transistors, 3-D integrated technique, low-profile magnetic substrates, and ceramic substrates with high thermal conductivity are considered. This paper discusses the characteristics of GaN transistors, including the fundamental differences between the enhancement mode and the depletion mode GaN transistors, gate driving, and the deadtime loss, the effect of parasitics on the performance of high-frequency GaN point-of-load (POLs), the 3-D copackage technique to integrate the active layer with low profile low temperature cofired ceramic magnetic substrate, and the thermal design of a high -density module using advanced substrates. The final demonstrators are three 12-1.2-V conversion POL modules: a single-phase 20 A 900 W/in3 2-MHz converter using enhancement mode GaN transistors, a single-phase10-A 800 W/in3 5-MHz converter, and a two-phase 20-A 1100 W/in3 5-MHz converter using the depletion mode GaN transistors. These converters offer unmatched power density compared to state-of-the-art industry products and research.

High-Frequency High Power Density 3-D Integrated Gallium-Nitride-Based Point of Load Module Design

The introduction of Gallium Nitride (GaN) based power devices offers the potential to achieve higher efficiency and higher switching frequencies than possible with Silicon MOSFET's. This paper will discuss the GaN device characteristics, packaging impact on performance, gate driving methods, and the integration possibilities using GaN technology. The final demonstration being an integrated 3D point of load (POL) converter operating at a switching frequency of 2MHz for a 12V to 1.2V buck converter with a full load current of 20A. This 3D converter employs a low profile low temperature co-fired ceramic (LTCC) inductor and can achieve a full load efficiency of 83% and a power density of 750W/in3 which doubles the power density of current integrated POL converters on the market today.

David Reusch

Papers

GaN Transistors for Efficient Power Conversion

Understanding the Effect of PCB Layout on Circuit Performance in a High-Frequency Gallium-Nitride-Based Point of Load Converter

Understanding the effect of PCB layout on circuit performance in a high frequency gallium nitride based point of load converter

High-Frequency High Power Density 3-D Integrated Gallium-Nitride-Based Point of Load Module Design

Gallium Nitride based 3D integrated non-isolated point of load module