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Wide-Input-Voltage-Range Dual-Output GaN-based Isolated DC-DC Converter for Aero-space Applications

Year: 2017 | Author: Xingye Liu | Paper: D3.4
Wire layout of DC converter
Fig. 1. Converter topology
In aerospace applications, a power converter may have to deal with harsh working conditions. These can include a wide input or output voltage range and a wide range of operation tempera-tures. This dc-dc converter is designed to accommodate a wide input voltage range and pro-vide two fixed output voltages. The new topology is designed with EPC GaN devices to divide the input voltages using an additional switch. The total volume is controlled and the efficiency is taken into account, and the converter shows peaks efficiency higher than 92&percnt when working at full power. The converter works just like a traditional active-clamp flyback circuit. The additional high-side switch needs additional design for its driving loop, but the operation mode does not change much. A few steps have been taken to design a planar transformer which fits the volume requirement and maintains good performance. Thanks to the new material ML91S from Hitachi, the transformer loss can be reduced, and a high-frequency converter with high efficiency and small volume can be realized.

With the current topology and operation level, the main challenge is efficiency over a wide range of input voltage. Even though the lowest and highest input occur at start-up and transient re-sponse, maintaining efficiency for input voltages from 18V to 70V still requires a significant tradeoff in design. In addition, the potential ability for control should be checked in order to limit the duty cycle to a reasonable range. In terms of efficiency, switches (or diodes) and transform-ers are the two main components responsible for most of the power loss. By selecting proper devices and designing a customized transformer, the whole range loss is controlled, but there is still some sacrifice at specific operation points.

In terms of manufacturing, the layout is critical, and gate driving loops for such devices on the primary side are more sensitive to noise than other converters. The final version of the converter has optimized the gate driving loop inductance and the layout is optimized for a smaller size and better power loop design.

Percent efficiency to input voltage. Waveforms shown for "with snubber", "without snubber", and "calculated"
Fig. 2. Converter efficiency

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