2018.11.22 SiC Power Device
In this article, as important points in utilizing full-SiC modules, in addition to the snubber capacitors that were discussed in the previous article we explain improvements to switching characteristics when a specialized gate driver is used.
Driving Specifications and Basic Configuration of Full-SiC Modules
The characteristics resulting when using snubber capacitors and specialized gate drivers are compared for the following conditions and circuit configuration. The circuit configuration is provided with the electrolytic capacitors and film capacitors described in the previous article. When a specialized gate driver is not used, as a false gate turn-on countermeasure, a capacitance CGS of microfarad order is added, and -5 V is applied to VGS as a negative bias (for the case of a full-SiC module equipped with second-generation SiC MOSFETs).
Specialized Gate Driver Board for Full-SiC Module Evaluation and Ceramic Snubber Capacitor Module
These are a specialized gate driver and snubber capacitor for addition to the above basic configuration. They are made available for use in evaluating full-SiC modules.
This is actual equipment with these components installed.
Effect of Specialized Gate Driver and Snubber Module
To begin with, waveforms are compared when the equipment is turned on, both before and after installing the specialized gate driver and the snubber capacitors.
In order from the top, the ID, VD, and VG waveforms are shown, with red and orange representing the waveforms for cases in which the specialized gate driver and the snubber module are installed, and the blue and green representing waveforms when they are not installed. It is clearly seen that surges and ringing are suppressed.
Next, the turn-off waveforms are shown.
Surges and ringing are likewise greatly reduced.
Where losses are concerned, Eon is increased from 4.3 mJ to 5.3 mJ, while Eoff is reduced from 5.3 mJ to 3.8 mJ. This is because with decreasing inductance, which exerts a large influence, Eon increases while Eoff decreases. On comparing the overall loss (Eon+Eoff), we see that loss is reduced by 0.4 mJ.
In conclusion, we can say that in order to fully utilize the performance of a full-SiC module, it is a good idea to add a snubber and use a gate driver with a specialized design. Up till now, taking as our theme important points in utilizing full-SiC modules, we have considered gate drivers and explained the effect of snubbers, and, in this article, the use of specialized gate drivers. In order to perform extremely high-speed switching of high voltages and large currents, the use of such complementary components, as well as adjustments based on evaluations, are important points. Particularly during initial evaluations, using an evaluation board and other tools can greatly smooth development.
・Surges and ringing can be dramatically suppressed by using a specialized gate driver and a snubber module.
・Where losses are concerned, there is an increase in Eon and a decrease in Eoff. When comparing overall losses (Eon+Eoff), losses are reduced.