Abstract：This paper proposed an isolated gate driving circuit for Silicon Carbide MOSFET, which could survive high environment temperature up to 200℃. In this circuit, bipolar junction transistors (BJTs) were used as switch devices instead of Si MOSFETs because high temperature would weaken their turn-off capability. This circuit included two branches, gate charging branch and gate discharging branch, by which the source driving signal of 0V/5V could be adjusted to driving level of -5V/18V. Each branch used a bootstrap capacitor to accelerate the BJT turn-on process, thereby speeding up the gate driving current. The equivalent model of the driving circuit was built. The equation for calculating four main passive components was obtained, and the relationship between the main passive components and BJT current amplification coefficients was available. Accordingly, the temperature compensation principle was introduced. With the load condition of 85V/14.5A, the results from double-pulse test under a series of step-up temperature points were obtained. The turn-on time of SiC MOSFET decreased from 133.6ns at room temperature to 112.4ns at 200℃, while the turn-off time increased from 99.2ns at room temperature to 109.8 ns at 200℃. The influence of temperature is that, with the increase of temperature, the transconductance of SiC MOSFET increases, and the Miller platform voltage declines, which in turn affects the turn-on and turn-off time.
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2018, Vol. 33 
