Research On Application Of GaN Power Transistors

The performance of silicon power devices have come to their theoretical limits and it is hard to satisfy the requirements requested by switching power supplies, which feature with high frequency, high efficiency and high power density. On behalf of the wide band semiconductors, Gallium nitride(Ga N) power transistors recieve widespread concern due to the fact that they enjoy fast switching capability, small parasitic parameters and excellent electric parameters. In recent years several manufacturers have developed the Ga N power transistor devices. Therefore it’s urgent to conduct the research on the application of Ga N power transistor.Firstly this paper analyses the advantages and disadvantages of high voltage Ga N and low voltage Ga N power transistor respectively. Low voltage enhancement Ga N power transistor has small size and small parasitic parameters, which makes it suitable in high frequency application. However its reverse conduction voltage drop is high and the range for driving voltage is narrow. The high voltage depletion Ga N power transistor has simple driving technique and good reverse recovery characteristic. However it cannot realize the strictly defined zero voltage switching for power switches, which restrains the increase of switching frequency to some extent.Based on the characteristic analysis, this paper proposes an improved three-level driving method for low voltage Ga N transistor applied in synchronous buck converter to solve the issue of high reverse conduction voltage drop and narrow driving voltage range. This method reasonably sets the dead time and takes the advantage of the false turn-on. This way, the reverse conduction power loss is decreased and the ringing on driving voltage is suppressed. A 12 V input, 1.2V/20 A output, 1MHz prototype is built to verify the analysis.For high voltage Ga N power transistor, this paper clarifies the effects of parasitic parameters of different packages on their performance in high frequency application and reaches the conclusion that surface mounted devices are more suitable for the high frequency application. Further this paper indicates that the small junction capacitor feature is beneficial to the decreasing of the dead time, which will help reduce the turn-off power loss and improve the conversion efficiency. A 400 V input, 12V/25 A output, 1MHz prototype is fabricated and the experimental results show that Ga N power transistor has superor high frequency switching capability and efficiency advantage compared to that of Si MOSFET.