Mitsubishi Electric has developed a highly accurate Simulation Program with Integrated Circuit Emphasis (SPICE) model to analyze the electronic circuitry of discrete silicon carbide SiC power devices.
The SiC SPICE model is deployed in the company’s N-series 1200V SiC MOSFET samples which will begin shipping in July. The model simulates high-speed-switching waveforms almost as well as actual measurements, says the company. This is expected to lead to more efficient circuit designs for power converters as Mitsubishi Electric adds several temperature-dependent parameters to enable its SiC SPICE model to work at high temperature.
The SiC MOSFET controls the current (drain current) flowing from the drain electrode to the source electrode depending on the voltage that is imposed on the gate electrode. The MOSFET has parasitic capacitances that accumulate charges and determine switching speed. When a voltage is applied to the electrodes of the device, the capacitance values change due to changes in distance between the layers that accumulate the positive and negative charge changes, resulting in changes in the switching speed. When the distance between layers decreases, the capacitance value increases and the switching speed decreases, and conversely, when the distance between layers increases, the capacitance value decreases and the switching speed increases.
The SiC SPICE model uses carefully evaluated voltage dependencies of the parasitic capacitances. These allow high-precision simulations of current waveforms during high-speed switching which was not achievable with the previous model. For example, for turn-on switching in which the SiC MOSFET switches from non-conducting to conducting, the simulated waveforms of all voltages and currents are in good agreement with actual experimental waveforms. The error in drain current rise has been reduced from 40 percent to 15 percent.
The new model enables high-precision simulation of the drain current flowing through the power conversion circuit over the entire rated current range. Circuit designers can spend less time complementing data with experiments, raising work efficiency from the early stages of power converter development. The new model also achieves high-precision simulation of the current waveform (gate current waveform) driving the SiC MOSFET, unlike in the past making it possible to reduce costs by selecting optimum devices that assure sufficient current for driving the SiC-MOSFET.
The 1200V N series SiC MOSFET uses junction field effect transistor (JFET) doping technology that reduces both switching loss and on-resistance, achieving a figure of merit (FOM) of 1,450mΩ·nC. Power consumption in power-supply systems is reduced by approximately 85 percent compared to using conventional Si-IGBTs. The devices start sampling in July 2020 and will include AEC-101 qualified parts for automotive on-board chargers in ewlectreic vehicles.
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