Stable cascode GaN HEMT operation by direct gate drive

We describe a proposed cascode GaN device configuration that allows stable operation during zero voltage switching (ZVS) turn-on transition and suppresses non-ZVS losses. We verified that application of our proposed device to an LLC resonant converter resulted in stable operation. In our device configuration, a GaN high-electron-mobility transistor (HEMT) gate is directly driven by a commercial Si MOSFET driver via a charge pump circuit. This allows the slew rate (dv/dt) to be controlled by an external gate resistance. In addition, we demonstrate that the 650-V normally-on GaN HEMT used in our proposed device configuration has highly reliable characteristics. The predicted lifetime for a 0.1% failure rate under actual bias conditions (Vds = 500 V at (150°C)) exceeds 1000 years (8.76 $\times $ 106)hr).