A High-Efficiency, High-Frequency Boost Converter using Enhancement Mode GaN DHFETs on Silicon

A boost converter was constructed using a high voltage enhancement mode (E-mode) AlGaN/GaN/AlGaN DHFET transistor grown on Si <111>. The very low dynamic on-resistance (R-dyn approximate to 0.23 Omega) and very low gate-charges (e.g. Q(gate) approximate to 15 nC at V-DS = 200 V) result in minor transistor losses. Together with a proper design of the passive components and the use of SiC diodes, very high overall efficiencies are reached. Measurements show high conversion efficiencies of 96.1% (P-out = 106 W, 76 to 142 V at 512.5 kHz) and 93.9% (P-out = 97.5 W, 78 to 142 V at 845.2 kHz). These are, to our knowledge, the highest efficiencies reported for an enhancement mode GaN DHFET on Si in this frequency range. The transistor switching losses are concentrated in the turn-on interval, and dominate at high frequencies. This is due to a limited positive gate-voltage swing, as the gate-source diode restricts the positive drive voltage.