Loss Distribution among Paralleled GaN HEMTs

Abstract

The market and opportunities are growing for GaN HEMTs in high-power applications. In many cases, GaN HEMTs need to be paralleled to increase the power capability or to enhance the efficiency. Unbalanced loss distribution among paralleled switches could cause overtemperature issues potentially, which will result in the derating of the power stage or even cause system failure. An analytical loss model is derived to analyze the tolerance of device characteristics variation for parallel. An auto-balancing mechanism for both switching loss and conduction loss is observed with paralleled GaN HEMTs due to the negative temperature coefficient of transconductance in the whole operating range. Stable operation is expected under all conditions without preselecting GaN HEMTs for parallel. Metal-core PCB based 240A/650V power modules are built with randomly selected GaN HEMTs and tested under high-power conditions. The junction temperatures of paralleled GaN HEMTs are measured to monitor the loss distribution, and the characteristic of GaN HEMTs in parallel is verified.