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29 Qorvo 2022 Introduction Silicon carbide (SiC) MOSFETs are firmly establishing themselves as a contender for the semiconductor switches in all stages of electric vehicle (EV) on-board chargers at power levels of 22kW and higher. The UnitedSiC (now Qorvo) SiC FETs, with their unique cascode construction of a Si MOSFET and SiC JFET, outperform IGBTs in efficiency, and are more attractive than superjunction MOSFETs. It's not just about overall converter system losses, though. Cost, size, and weight are also important factors that matter to an EV owner. Designers have a choice of different package styles for semiconductor power switches in EV on-board chargers, including surface mount variants that can be viable up to tens of kW when SiC FETs are used. In this blog, we will look at some SiC FET performance figures. SiC FETs in OBC Chargers At the typical power levels seen in EVs, even with 98%+ efficiency, on-board chargers still need to dissipate hundreds of watts from a small housing in a hot environment. As a result, heatsinking is needed, often with liquid cooling. A major design consideration is how the switches connect to this heatsinking arrangement for optimal thermal transfer, yield reliability, and low assembly cost. It is common to find SiC FETs in a TO-247-4L package that delivers excellent thermal performance, around 1.0°C/W from the junction to the cooling fluid, using UnitedSiC (now Qorvo)'s wafer-thinning technology with a silver-sinter die and a ceramic isolator pad. However, a downside of the TO-247-4L package is that it needs mechanical fixing and through-hole soldering. It also has significant package inductance and limited creepage and clearance between its pins. In addition, the package has less distance between PCB pads unless the leads are 'joggled' in a complicated and expensive way. SiC FETs in OBC Chargers Good Things Come in Small Packages (Source: Qorvo) Semiconductor power switches in EV on-board chargers and surface mount variants can be viable up to tens of kW when SiC FETs are used. We will look at some performance figures. Mike Zhu Senior Product Apps Engineer, Qorvo