GaN HEMT Gate Driver Circuit Utilizing Variable Capacitors

Active gate drivers promise lowered switching energies, decreased over-voltages, and improved system EMI. Controllability of gate charging process in available active drivers is limited by discrete, multi-step changes in voltage and gate resistance, or single-shot pulsed charge injection. This work investigates using a charge-coupled variable capacitor instead, to drive a GaN transistor with a controllable, near-linear current source gate driver. The proposed circuit can potentially offer higher efficiency than a standard voltage source driver, without introducing duty cycle or switching frequency limitations as in e.g. resonant gate drivers. Due to the current lack of suitable commercially available variable capacitors it is an exploratory work, utilizing a custom plate capacitor driven by an electric motor to experimentally validate the concept.