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Increasing efficiency and shrinking GaN devices

Nov 19, 2012
Fraunhofer ISE has explored the limits of a new technology with gallium nitride power transistors

Scientists at the Fraunhofer Institute for Solar Energy Systems ISE have successfully tested new types of power transistors made of gallium nitride in power electronic systems.

With these transistors, the size of charging inverters for electric vehicles and the weight of power converters for aircrafts can be reduced and power supplies for server farms could gain efficiency.

Fraunhofer ISE 1MHz LLC resonant converter

Gallium nitride (GaN) has been in the centre of interest of many semiconductor researchers for a long time.

“With power transistors made of GaN, significantly higher switching frequencies are achievable than with ordinary silicon power transistors. In contrast to SiC, GaN is particularly suited for the lower voltage range. Especially resonant topologies can fully utilise the advantages of GaN power transistors,” says Bruno Burger, head of the department “Power Electronics” at Fraunhofer ISE.

Despite the substantial need for research, impressing results have been obtained in an internal study. A DC/DC converter with rated output power of one kilowatt was operated at a switching frequency of one megahertz providing 94 percent peak efficiency. “With regard to the 600V GaN transistor the switching frequency and also the efficiency of the DC/DC converter could have been raised to an even higher level. The limiting factor was the high-frequency transformer,” points out Arne Hendrik Wienhausen who performed the experiments.

Until today, only transistors made of silicon have been used in power electronic systems with voltages up to 600V. Switching and conduction losses of these transistors are significantly higher than those of transistors made of GaN. Therefore high losses are generated in the transistors which need to be dissipated in a complex way.

In addition to the higher efficiency, GaN provides the opportunity of increasing the switching frequency to exceed the state-of-the-art multiple fold. As a result, the passive components like inductors, transformers and capacitors can be much smaller leading to more compact and light-weight designs and expensive materials can be saved.

The scientists at Fraunhofer ISE predict that GaN will permanently change the world of power electronics. In all applications where system weight and volume are crucial, power transistors made of GaN and operated at high frequency offer great advantages over other technologies. It can be assumed that the switching frequency of one megahertz demonstrated in the DC/DC converter is only a first step towards much higher switching frequencies while maintaining high efficiency.

Converter efficiency of the 1MHz LLC resonant converter

The GaN power transistors used in the converter were produced by Panasonic.
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