This article was published in full in IEEE Transactions on Transportation Electrification.

Authors: R. Hou, Y. Shen, H. Zhao, H. Hu, J. Lu and T. Long

Gallium Nitride enhancement-mode high electron mobility transistors (GaN E-HEMTs) can achieve high frequency and high efficiency due to its excellent switching performance compared with conventional Si transistors. Nevertheless, GaN HEMTs exhibit a more pronounced dynamic on-state resistance RDS(on) than silicon transistors. The variation of RDS(on) is caused by both the static RDS(on) due to junction temperature rise and the dynamic RDS(on) due to the electron trapping.

Without a careful decoupling analysis, it is difficult to calculate and model the dynamic RDS(on) portion. This paper introduces a comprehensive approach of dynamic RDS(on) evaluation, comprising four techniques: 1) a clamping circuit for both the hard-switching (HS) device and synchronous rectification (SR) device; 2) a junction temperature monitoring technique; 3) control of both the pulse test and soak time; 4) continuous operation of device under test.

Based on the dynamic RDS(on) test results, a new model of the RDS(on) variation is developed where two coefficients: kTj and kdR are defined to model the contribution of the heating effect and the impact of the trapping effect, respectively. The RDS(on) model is validated by the comparison between the calculated and measured junction temperatures of a 650 V/30 A GaN-based half-bridge. Furthermore, a detailed loss breakdown analysis is conducted for the GaN-based hard-switching half-bridge. Results show that the switching losses, Eon and Eoff are the dominant loss factors with high switching frequency. At last, the possible efficiency improvements are also discussed in detail.

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