Design considerations for a self-powered gate driver for normally-ON SiC junction field-effect transistors

The very low on-state resistance, the voltage-controlled gate, and the relative simplicity of fabrication of the normally-ON silicon carbide junction field effect transistor make this device the most important player among all state-of-the-art silicon carbide transistors. However, the normally-ON nature counts as the main factor which keeps this device far from being considered as an alternative to the silicon insulated-gate bipolar transistor. A self-powered gate driver without external power supply for normally-ON silicon carbide junction field effect transistors is presented in this paper. The proposed circuit is able to handle the shoot-through current when the devices are subjected to the dc-link voltage by utilizing the energy associated with this current. On the other hand it supplies the necessary negative gate-source voltage during the steady-state operation. A detailed description of the operating states of the proposed circuit along with various design considerations are presented. From experiments which were performed in a half-bridge converter, it is shown that the shoot-through current can be turned off within approximately 15 μs. Moreover, it is shown that the proposed gate driver can properly switch the devices.