Switching Characteristics of Gallium Nitride Transistors: System-Level Issues

Abstract

The use of gallium nitride devices is gathering momentum, with a number of recent market introductions for a wide range of applications such as point-of-load (POL) converters, off-line switching power supplies, battery chargers, and motor drives. GaN devices have a much lower gate charge and lower output capacitance than silicon MOSFETs and, therefore, are capable of operating at a switching frequency 10 times greater. This can significantly impact the power density of power converters, their form factor, and even current design and manufacturing practices. To realize the benefits of GaN devices resulting from significantly higher operating frequencies, a number of issues have to be addressed, such as converter topology, magnetics, control, packaging , and thermal management. This chapter studies the switching characteristics of high-voltage GaN devices including some specific issues related to the cascode GaN. An evaluation is presented of the cascode GaN based on a buck converter in hard-switching and soft-switching modes, which shows the necessity of soft switching for cascode GaN devices at high frequencies. High dv/dt- and di/dt-related gate drive issues associated with the higher switching speed of GaN devices are addressed, and many important design considerations are presented. Additionally, this chapter illustrates the utilization of GaN in a wide range of emerging applications.