The vehicle electrification drive, where every pound matters, is increasingly looking toward two wide bandgap semiconductor technologies: silicon carbide (SiC) and gallium nitride (GaN). These semiconductor materials can withstand much higher voltages and temperatures than silicon and thus offer greater reliability and durability while using less energy.
Converters and inverters in electric vehicles. Image via Yole.
The SiC-based MOSFETs are already replacing silicon IGBTs in the main inverters that convert battery voltage into 3-phase AC voltage to drive motor. Wolfspeed, for example, has recently supplied the SiC power module to Ford for powertrain in electric vehicle (EV). The 400-A power module contains four MOSFETs connected in parallel to achieve 2.5 mΩ Rds(on); the module is designed around the 900 V, 10 mΩ chip. Wolfspeed has also demonstrated these chips to create an 800 A, 1.25 mΩ module.
It’s worth noting that Wolfspeed, a unit of Cree, has already been offering SiC components for on-board charging and DC-to-DC power conversion systems in EVs. The SiC module, compared to IGBT modules, reduce switching losses by as much as 75 percent. That makes the inverter significantly smaller and lighter by boosting power throughput as well as thermal management. Moreover, lower switching losses contribute to a more compact cooling system.
So while SiC components are steadily gaining adoption in electric vehicles, where do GaN chips stand? The market research firm Yole sees the charging of the high-voltage drive battery, the DC-AC auxiliary power supply, and the DC-DC buck conversion to 12 V and 48 V battery as potential markets for GaN due to its high-speed switching capability.
Transphorm is a case in point. The supplier of high-voltage GaN FETs has recently secured a $15 million investment from Yaskawa Electric. Earlier, in March 2017, Transphorm unveiled a 650V chip that according to the company is the first GaN solution to earn automotive qualification.
Transphorm’s GaN FET has passed the AEC-Q101 stress tests for automotive-grade discrete semiconductors. The chipmaker is targeting the TPH3205WSBQA chip for on-board charger and DC-to-DC systems in plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEV).
The choice between SiC and GaN components generally depends on a lot of design considerations. However, SiC chips are considered more suitable for high-power DC/AC inverters and DC/DC converters. And GaN components are more adaptable to low- to medium-power DC/DC and AC/DC converters.
In 2018, industry watchers are anticipating a lot of momentum for vehicle electrification, especially for hybrid electric vehicles. Both SiC and GaN power components are likely to be an important part of this automotive industry upheaval.
Majeed Ahmad is the former Editor-in-Chief of EE Times Asia. He is a journalist with an engineering background and two decades of experience in writing and editing technical content. He is also the author of six books on electronics: Smartphone, Nokia’s Smartphone Problem, The Next Web of 50 Billion Devices, Mobile Commerce 2.0, Age of Mobile Data, and Essential 4G Guide.