For several years, the Fraunhofer Institute for Applied Solid State Physics IAF has been conducting research on monolithic integration in the field of GaN-based power electronics. Back in 2014, the integrated intrinsic freewheeling diodes and gate drivers on a 600 V-class power transistor. In 2017, a monolithic GaN half bridge was then operated at 400 V for the first time. With their latest research results, current and temperature sensors are now being added.
As part of the GaNIAL research project, the researchers have provided functional verification of full functionality in a GaN power IC. The full title of the GaNIAL project is »Integrated and efficient power electronics based on gallium nitride«. The project is funded by the German Federal Ministry of Education and Research; since 2016, this collaboration between Fraunhofer IAF and the BMW Group, Robert Bosch, Finepower and the University of Stuttgart has been working to develop powerful, compact GaN-based components for electromobility.
Project partner Finepower will be displaying the newly developed GaN power module at this year’s PCIM Europe (Hall 9, booth 440). Researchers from Fraunhofer IAF will unveil their latest research results and developments in the field of power electronics at the accompanying conference.
Integrated sensors for direct control
Compared to conventional power converters, the newly developed circuit simultaneously not only enables higher switching frequencies and a higher power density; it also provides fast and accurate condition monitoring within the chip itself. »Although the increased switching frequency of GaN-based power electronics allows for increasingly compact designs, this results in higher requirements for monitoring and control. This means that having sensors integrated within the same chip is a considerable advantage«, emphasizes Stefan Mönch, a researcher in the Power Electronics business unit at Fraunhofer IAF.
Previously, current and temperature sensors were implemented outside the GaN chip. Thanks to the integrated current sensor, the transistor current can be measured reaction-free for regulation and for short-circuit protection, and space is saved compared to conventional external current sensors. By the integrated temperature sensor the temperature of the power transistor can be measured directly. This enables this thermally critical point to be mapped much more accurately and quickly than previous external sensors, since the distance and resulting temperature difference between sensor and measuring-point is eliminated by the monolithic integration.
»The monolithic integration of the GaN power electronics with sensors and control circuit saves space on the chip surface, reduces the outlay on assembly and improves reliability. For applications that require lots of very small, efficient systems to be installed in limited space, such as in electromobility, this is crucial«, says Mönch, who designed the integrated circuit for the GaN chip. Measuring just 4 mm x 3 mm, the GaN chip might be the basis for the further development of more compact on-board chargers. This development might pave the way for more compact and efficient on-board chargers in electric vehicles. As this charging technology is carried in the vehicle, it must be as small and lightweight as possible, and also cost-efficient. It therefore requires extremely compact yet efficient power electronics systems.