Evaluation of Trench-Gate Bipolar-Mode JFETs Used as High-Side Transistors in Low-Voltage Buck Converters

For the first time, power loss comparison between 20V-rated devices including a trench MOSFET and four kinds of trench-gate bipolar-mode JFETs (TB-JFETs) was carried out with the help of simulation based on static analysis and mixed-mode dynamic analysis using an inductive switching circuit. With at least 14% power loss improvement at 1 MHz and 19% at 2 MHz compared to that of the trench MOSFET, the calculation results have generated the confidence to take normally-on TB-JFETs, especially the one with buried oxide (BOX) to reduce the gate-drain capacitance C_GD which can provide 6% more improvement at both 1 and 2 MHz, as competitive candidates to replace trench MOSFETs as a high-side switch in low-voltage high-frequency buck converters. Experimental data of C_GD for normally-on JFETs with and without BOX agree to the simulated results and account for the extra improvement in dynamic loss provided by the device with BOX. On the other hand, the normally-off devices (with and without BOX) always perform the worst within the commonly used frequency range, which implies their uselessness.