Silicon Carbide (SiC) power semiconductors are rapidly emerging in the commercial market. These devices offer several benefits over conventional Silicon-based power semiconductors. SiC MOSFETs can improve overall system efficiency by more than 10%, and the higher switching capability can reduce the overall system size and cost.

Avago Technologies gate drive optocouplers are used extensively to drive Silicon-based semiconductors like IGBT and Power MOSFETs. Optocouplers are used to provide reinforced galvanic insulation between the control circuits from the high voltages and the power semiconductors. The ability to reject high common mode noise (CMR) will prevent erroneous driving of the power semiconductors during high frequency switching. We will discuss how the next generation of gate drive optocouplers can be used to protect and drive SiC MOSFETs.

Silicon Carbide is a wide bandgap (3.2 eV) compound. Wide-bandgap SiC, besides being able to operate at high voltage, frequency and temperature, exhibits on-resistance and gate charge by an order of magnitude lower than silicon material. In an evaluation conducted by CREE to compare the second generation 1200 V/20 A SiC MOSFET with a silicon high speed 1200 V/40 A H3 IGBT using a 10 KW hard-switching interleaved boost dc-to-dc converter, the results showed that even with five times the switching frequency, the SiC solution was able to achieve a maximum efficiency of 99.3% at 100 KHz, reducing losses by 18% from the best efficiency of the IGBT solution at 20 KHz.

CREE’s recent release of the C2M family of MOSFETs give engineers a wide range of competitively priced 1200 V and 1700 V SiC MOSFETs for a wide range of applications.  Cree has been able to bring the MOSFET’s cost down significantly, while providing improved switching performance and lower Rds (on).  Increasing the switching frequency can significantly reduce the size of the inductor. The lower conduction and switching losses allow engineers to reduce the size of the heat sink, or potentially remove fans and move to passive cooling solutions. Although a SiC semiconductor costs more than Si, the overall system BOM costs can be lower than Si technology by 20%.