Negative bias supply is another common requirement for driving SiC MOSFETs. High-power applications may result in high dv/dt that induces current through the Miller capacitances of the SiC MOSFET and charges the gate of the SiC MOSFET. The SiC MOSFET can inadvertently turn on and result in destructive consequences. Negative bias voltage can be used to prevent spikes from reaching the turn-on threshold, verifying that the SiC MOSFET stays off (also known as bipolar drive). Figure 3-2 shows how a transient 2.5V spike can affect a SiC MOSFET with a 2.5V gate-source threshold: using 0V turn-off results in accidental turn-on, while using -5V turn-off verifies that the SiC MOSFET stays off.

Figure 3-2 Turn-Off Level Comparison