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GaN voltage regulator on a chip: 10 times higher switching frequency

GaN voltage regulator on a chip: 10 times higher switching frequency

Technology News |
By Christoph Hammerschmidt



In monolithic integration, several components are combined on a single GaN chip. This allows particularly small, space-saving systems. Monolithic integration makes the half-bridge circuitry not only very compact, but also significantly improves the electronic properties: for example, the switching frequency can be increased by a factor of 10 by comparison with conventional voltage transformers. “With a switching frequency of up to 3 MHz, we can achieve a much higher power density. This is very important, among other things, in electromobility, where many, as efficient converters have to be installed in a small space,” says Richard Reiner, research assistant at the Fraunhofer IAF (Freiburg, Germany). The monolithic integrated half-bridge saves chip area, reduces the assembly complexity and increases the reliability.

In their R&D project, the Fraunhofer researchers already had a specific application field in mind: Electric vehicles. Because to make such vehicles suitable for mass markets, it takes not only powerful and affordable batteries. E-cars must be lightweight and as economical as possible in terms of energy consumption. This is only possible with novel semiconductor materials such as gallium nitride (GaN), which offers a significant advantage over the competing (and currently more mature) silicon carbide (SiC), says Fraunhofer. GaN enables higher power densities and higher energy efficiency for electronic components in electric vehicles. The aim of automotive manufacturers and users is to develop as small, highly efficient on-board chargers for electric vehicles as possible.

 

The compact design reduces negative influences such as, for example, line impedances. This improves the electrical switching characteristics. The integration of additional sensors, such as a thermal monitoring system, allows for optimized operation. “With this innovative approach, we can achieve a new level of performance, efficiency, robustness, functionality and reliability in electric mobility,” explains Dr. Patrick Waltereit, Deputy Business Unit Manager for Power Electronics at Fraunhofer IAF.

 

The half-bridge circuit of the Fraunhofer IAF consists of two GaN HEMTs (high-electron mobility transistors) and two integrated free-wheel diodes. The HEMTs feature a blocking voltage of over 600 volts and a transmission resistance of 120 mΩ. A folded chip layout allows tight connection of a DC link capacitance between supply voltage and ground. This design allows an optimized power path and vibration-free switching at high frequencies. The operation of this circuit was demonstrated in a down converter from 400 to 200 volts at a switching frequency of 3 MHz.

Even more complex circuits such as a monolithically integrated multilevel inverter have already been implemented in this GaN-on-Si technology. In this topology, ten GaN circuit breakers are located on a chip with the area of 2 × 3 mm 2. Each switch has a blocking voltage of 400 V and a resistance of 350 mΩ in the forward mode. Compared to conventional converters, multilevel inverters generate smaller noise levels during DC / AC conversion. As a result, interference suppression and output filters can be dimensioned smaller. Thus, the monolithic integration not only reduces the cost but makes the voltage converters more compact and lighter. The function of this converter could be demonstrated in inverter operation with American mains voltage (120 V).

The monolithic integrated half-bridge circuit will be presented by Fraunhofer IAF from 16 to 18 May 2017 at PCIM Europe in Nuremberg (Hall 7, Stand 237).

More information: https://www.iaf.fraunhofer.de/en.html

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