It is well established that the CMOS inverter and DRAM are the two basic building blocks of digital signal processing. Decades of improving inverter switching speed and memory density under Moore's Law has unearthed numerous applications that were previously unimaginable. Power processing is built upon two similar functional building blocks: power switches and energy storage devices, such as the inductor and capacitor. The push for higher switching frequencies has always been a major catalyst for performance improvement and size reduction.

Since its introduction in the mid‐1970s, the power MOSFET, with its greater switching speed, has replaced the bipolar transistor. To date, the power MOSFET has been perfected up to its theoretical limit. Device switching losses can be reduced further with the help of soft‐switching techniques. However, its gate‐drive loss is still excessive, limiting the switching frequency to the low hundreds of kilohertz in most applications.

The recent introduction of GaN, with much improved figures of merit, opens the door for operating frequencies well into the megahertz range. A number of design examples are illustrated in this book and other literatures, citing impressive power density improvements by a factor of 5 or 10. However, I believe the potential contribution of GaN goes beyond the simple measures of efficiency and power density. GaN has the potential to have a profound impact on our design practice, including a possible paradigm shift.

Power electronics is interdisciplinary. The essential constituencies of a power electronics system include switches, energy storage devices, circuit topology, system packaging, electromagnetic interactions, thermal management, EMC/EMI, and manufacturing considerations. When the switching frequency is low, these various constituencies are loosely coupled. Current design practices address these issues in piecemeal fashion. When a system is designed for a much higher frequency, the components are arranged in close proximity to minimize undesirable parasitics. This invariably leads to unwanted electromagnetic coupling and thermal interaction.

This increasing intricacy between components and circuits requires a more holistic approach, concurrently taking into account all electrical, mechanical, electromagnetic, and thermal considerations. Furthermore, all operations should be executed correctly, both spatially and temporally. These challenges would prompt circuit designers to pursue a more integrated approach. For power electronics, integration will take place at the functional level or the subsystem level whenever feasible and practical. These integrated modules will serve as the basic building blocks of further system integration. In this manner, customization can be achieved using standardized building blocks, in much the same way as digital electronics systems. With the economy of scale in manufacturing, this will bring significant cost reduction in power electronics equipment and unearth numerous new applications previously precluded due to high cost.

GaN will create fertile ground for research and technology innovations for years to come. Dr. Alex Lidow mentions in this book that it took 30 years for power MOSFET to reach its current state of maturity. While GaN is still in an early stage of development, a few technical challenges require immediate attention. These issues are recognized by the authors and addressed in the book.

1. High dv/dt and high di/dt render most of the commercially available gate drive circuits unsuitable for GaN devices, especially for the high‐side switch. Chapter 3 offers many important insights into the design of the gate drive circuit.
2. Device packaging and circuit layout are critical. The unwanted effects of parasitics should be contained. Soft‐switching techniques can be very useful for this purpose. A number of important issues related to packaging and layout are addressed in detail in Chapters 4 to 6.
3. High‐frequency magnetic design is critical. The choice of suitable magnetics materials becomes rather limited when the switching frequency goes beyond 2–3 MHz. Additionally, more creative high‐frequency magnetics design practice should be explored. Several recent publications suggest design practices that defy the conventional wisdom and practice, yielding interesting results.
4. The impact of high frequency to EMI/EMC has yet to be explored.

Dr. Alex Lidow is a well‐respected leader in the field. Alex has always been in the forefront of technology and a trendsetter. While serving as the CEO of International Rectifier, he initiated GaN development in the early 2000s. He also led the team in developing the first integrated DrMOS and DirectFET®, which are now commonly used in powering the new generation of microprocessors and many other applications.

This book is a gift to power electronics engineers. It offers a comprehensive view, from device physics, characteristics, and modeling to device and circuit layout considerations and gate drive design, with design considerations for both hard switching and soft switching. Additionally, it further illustrates the utilization of GaN in a wide range of emerging applications.

It is very gratifying to note that three of the five authors of this book are from CPES, joining with Dr. Lidow in the effort to develop this new generation of wide‐band‐gap power switches – presumably a game‐changing device with a scale of impact yet to be defined.

The authors wish to acknowledge the many exceptional contributions toward the content of this book from our colleagues.

Dr. Edward Jones contributed to Chapters 3, 6, and 7 with significant content and excellent insights into these as well as several other chapters. Dr. Yuanzhe Zhang is the resident expert on envelope tracking and created much of the work behind Chapter 14 as well as numerous insights and suggestions on other chapters. Dr. Suvankar Biswas did work supporting Chapters 5, 10, and 11. Steve Colino was the driving force behind our class D audio in Chapter 12, while giving many suggestions and insights into almost every chapter. Mohamed Ahmed, in addition to being a star Ph.D. candidate at Virginia Tech, was a brilliant intern for EPC during the summer of 2018 and did much of the experimental work behind the LLC converters in Chapter 10.

We would also like to acknowledge Jianjun (Joe) Cao, Robert Beach, Alana Nakata, Guang Yuan Zhao, Yanping Ma, Robert Strittmatter, and Seshadri Kolluri for providing much of the technical foundation behind GaN transistors and integrated circuits.

A special thank you is due to Joe Engle who, in addition to reviewing and editing all corners of this work, put all the logistics together to make it happen. Sometimes this logistics meant long continuous hours of editing, coupled with amazing diplomacy working with a wide spectrum of personalities. Jenny Somers, the lead graphic artist on this work, as well as many other GaN‐related papers and application notes, deserves a medal of honor as well as an honorary degree in GaN for her creative, and extremely accurate, projection of scientific data into documentary communications.

A note of gratitude to the editors and staff at Wiley who were instrumental in undertaking a diligent review of the text and shepherding the book through the production process.

Finally, we would like to thank Archie Huang and Sue Lin for believing in GaN from the beginning. Their vision and support will change the semiconductor industry forever.