Evaluation and application of 600V GaN HEMT in cascode structure

Gallium nitride high electron mobility transistor (GaN HEMT) has matured dramatically over the last few years. More and more devices have been manufactured and field in applications ranging from low power voltage regulator to high power infrastructure base-stations. Compared to the state of art silicon MOSFET, GaN HEMT has much better figure of merit and is potential for high frequency application. In general, 600V GaN HEMT is intrinsically normally-on device. To easily apply depletion mode GaN HEMT in circuit design, a low voltage silicon MOSFET is in series to drive the GaN HEMT, which is well known as cascode structure. This paper studies the characteristics and operation principles of 600V cascode GaN HEMT. Evaluations of GaN HEMT performance based on Buck converter under hard-switching and soft-switching conditions are presented. Experimental results illustrate that GaN HEMT is superior than silicon MOSFET but still needs soft-switching in high frequency operation due to considerable package and layout parasitic inductors and capacitors. Then GaN HEMT is applied to a 1MHz 300W 400V/12V LLC converter. Comparison of experimental results with state of art silicon MOSFET is provided to validate the advantages of GaN HEMT.