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Isolated DC-DC Converters with eGaN® FETs
Keywords: Gallium Nitride, Isolated DC-DC Converters, High Frequency
The intermediate bus architecture (IBA) is currently the most popular power system architecture in computing and telecommunications equipment. It typically consists of a +48 V system power distribution bus that feeds on-board isolated converters, which in turn supply power to a 12 V power bus. In this paper we demonstrate substantial performance gains achieved in isolated DC-DC converters using enhancement mode gallium nitride power transistors that have been commercially available for over three years. These transistors, also known as eGaN® FETs are making significant inroads replacing the aging silicon power MOSFET. Two topologies are explored; a full bridge topology [1] and a soft-switched resonant topology [2]. The fully regulated eGaN FET-based full bridge topology is able to operate at much higher frequencies and produce higher power densities than corresponding isolated converters using power MOSFETs. Using eGaN FETs for the primary side devices, 60% lower output charge (QOSS) losses and a staggering 93% reduction in switching figure of merit (FOM) (RDS(ON) x QGD) can be achieved. This paper will also demonstrate the ability of the eGaN FET to improve efficiency and output power density in a high frequency soft switching application, as compared to what is achievable with existing power MOSFET devices. An isolated 48 V intermediate bus converter (IBC) with a nominal 12 V output utilizing a resonant topology operating above 1 MHz is presented. Due to almost a factor of 2 decrease in output charge provided by the primary and secondary eGaN FETs compared to state of the art MOSFETs, the ZVS transition is achieved in a proportionally shorter period, increasing the effective duty cycle and improving the overall converter performance. The eGaN FET-based converter is able to deliver over 375 W compared with 310 W for the silicon-based resonant circuit. A significant savings can be realized by adopting the new generation of isolated DC-DC converters that use gallium nitride-based transistors. The two examples presented here each enable a 20 percent efficiency improvement in addition to tighter regulation, faster transient response, and higher power density.
David Reusch, Director of Applications Engineering
Efficient Power Conversion (EPC)
Blacksburg, Virginia

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