Silicon Carbide (SiC), aka Carborundum, is a silicon and carbon chemical compound. Its material properties enable SiC devices to have high blocking voltage capabilities and low specific ON resistance. Such properties allow superfast switching speeds and the ability to operate at high temperatures, making SiC a viable successor to traditional silicon-based (Si) devices in power electronics. The technology can be adapted into prominent applications, such as automotive EV/HEV and charging, solar and energy storage systems, data and communications power and UPS, industrial drives, HVAC, and welding.
Schottky diodes (SBDs) and MOSFETs are commonly specified SiC devices. SiC devices have five critical advantages over Si devices:
- The switching frequency of the power converter influences factors such as switching losses, transformer losses, overall converter size/weight, and converter level electromagnetic interference (EMI). Compared to Si switches, SiC MOSFETs have low switching loss energy and ultra-low gate charge, which enables a higher switching frequency for a more compact transformer design with reduced power loss.
- The ON resistance (RDS(ON)) is the resistance between the source and the drain of a MOSFET. The lower the ON resistance, the lower the power loss. A low RDS(ON) also translates to lower heat generation. The specific ON resistance of 1700 V SiC MOSFETs is much lower than that of 2000 V and above-rated Si MOSFETs. Smaller packages can be used, with the same ON resistance rating, thereby improving the cost-performance of a 1700 V SiC MOSFET. SiC SBDs offer more rugged performance at junction temperatures (TJ) above 150 °C.
- SiC MOSFETs have lower switching losses than Si MOSFETs, which can improve converter efficiency. The heatsink can be reduced in size or even removed altogether. Lower switching losses also provide an option to increase the switching frequency of the auxiliary power supply to minimize transformer size and weight. Ultra-low switching losses and fast switching speed can support a significant increase in energy efficiency.
- SiC devices have a wide bandgap; bandgap refers to the difference in energy between the top of the valence band and the bottom of the conduction band. The large distance enables devices to operate at higher voltages, temperatures, and frequencies. DiscreteSiC Schottky diode and SiC MOSFETs devices have wide-bandgap (4H-SiC has 3.3eV) that allow low conduction and switching losses. In comparing SiC and Si semiconductor dies with identical structures and dimensions, the SiC die exhibits a lower specific ON resistance and a higher breakdown voltage than the Si die.
- SiC has a thermal conductivity that improves upon common Si by a factor of three. SiC can also tolerate voltages up to 10 times higher than ordinary Si. Improved thermal conductivity can lead to reduced system complexity and cost. SiC MOSFET devices blend high operating voltages and fast switching speeds, a combination typically not available with traditional power transistors.
As depicted in the Figure 1, SiC devices exhibit low switching and conduction losses, resulting in smaller component sizes and improved power density. They operate at high junction temperatures and feature low gate resistance, low gate charge, low output capacitance, and ultra-low ON resistance.
Figure 1: Converter-level benefits Source: [Littelfuse: Unleash SiCMOSFETs- Extract the Best Performance]
Littelfuse SiC Schottky Diodes, such as the LSIC2SD065CxxA and LSIC2SD065AxxA series, are available with a variety of current ratings (6A, 8A, 10A, 16A or 20A). They offer power electronics system designers a variety of performance advantages, including negligible reverse recovery current, high surge capability, and a maximum operating junction temperature of 175°C; specifications that make them suitable for enhanced efficiency, reliability, and thermal management applications.
The SiC MOSFET device structure enables lower per-cycle switching losses and improved light load efficiency when compared to similarly rated IGBTs. SiC’s inherent material properties allow SiC MOSFETs to outperform similarly rated Si MOSFETs in terms of blocking voltage, specific resistance, and junction capacitances. The Littelfuse LSIC1MO170E0750 is an N-Channel SiC MOSFET supporting a maximum drain to source voltage (Vds) of 1700V, ON resistance (RDS(ON)) of 750 mΩ, and a maximum operating junction temperature of 175 ºC. Its pin arrangement simplifies the PCB routing and the Kelvin source connection reduces stray inductance in the gate drive circuit, improving efficiency, EMI behavior, and switching performance.