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Loss Analysis of 600V Gallium Nitride HEMT in Cascode Structure with Simulation Model

Fig. 1. GaN HEMT cascode structure and package parasitic inductance.
The emerging Gallium Nitride (GaN) high electron mobility transistor (HEMT) is considered as a promising candidate for future power conversion technology due to its much better figure of merit when compared to the state-of-the-art silicon MOSFET. So far in high voltage range, the GaN HEMT in cascode structure (Fig. 1) is widely used. In order to better evaluate the characteristics of the 600V GaN HEMT in cascode structure, a good behavior level simulation model is in need. This paper presents the development of simulation model for the 600V cascode GaN HEMT. A method is proposed to accurately extract the device package parasitic inductance, which is of vital importance to better predict the high frequency performance of the device. The accuracy of the simulation model is verified by the experiment. The simulation results match well with the experiment in both switching waveforms (Fig. 2) and switching loss. Based on the simulation model, a detailed Buck converter loss breakdown (Fig. 3) is made, which indicates that the switching loss is dominant in hard switching conditions; and soft switching is still critical to achieve the high frequency and high efficiency operation of the high voltage cascode GaN HEMT.

Fig. 2. GaN HEMT switching waveforms matching between simulation and experiment.


Fig. 3. Buck converter efficiency and loss breakdown at Vin=380V, Vout=200V condition.
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