Novel AC coupled gate driver for ultra fast switching of normally-off SiC JFETs

Abstract

Over the last years, more and more SiC power semiconductor switches became available in low production volumes in order to prove their superior behavior with respect to fast switching speed, low on-resistance per chip area, high voltage range and high temperature operation. A very promising device among those introduced in numerous publications over the last years is the 1200 V 30 A JFET introduced by SemiSouth. It features a very low on-resistance (2.8m Ω cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), switching operation within 20 ns, a normally-off characteristic and has already been commercialized in contrast to many other SiC switches. To fully exploit the potential of the SiC normally-off JFET, conventional gate drivers for unipolar devices must be adapted to this device due to its special requirements: During on-state the gate voltage must not exceed 3 V, while a current of around 300 mA must be fed into the gate, during switching operation the transient gate voltage should be around ±15 V and the low threshold voltage of 0.7 V requires a high noise immunity which is a severe challenge as the device has a comparably low gate-source but high gate-drain capacitance. To meet these requirements, several concepts have been published recently. They deal with the challenges mentioned, but they also note certain limitations (e. g. frequency and duty cycle limitations or need for additional cooling). In this paper, a novel gate driver consisting only of one standard gate driver IC, resistors, capacitors and diodes is designed and experimentally validated. It supplies enough gate current for minimum on-resistance, allows fast switching operation, features a high noise immunity and can be used for any duty cycle and usual switching frequencies without significant self-heating.