eGaN® FETs in Wireless Power Transfer Systems
●INTRODUCTION
■The popularity of wireless energy transfer has increased over the last few years and in particular for applications targeting portable device charging. In this article, the focus will be on loosely coupled coils, highly-resonant wireless solutions suitable for the A4WP [1] standard operating at either 6.78 MHz or 13.56 MHz unlicensed Industrial, Scientific and Medical (ISM) [2] band.
■Many of the wireless energy transfer solutions have targeted portable device charging that require features such as low profile, high efficiency, robustness to changing operating conditions and, in some cases, light weight. These requirements translate into designs that need to be efficient and able to operate without a bulky heatsink. Furthermore the design must be able to operate over a wide range of coupling and load variations. There are a few amplifier topologies that can be considered such as the voltage mode class-D, current mode class-D and class-E. The class-E has become the choice for many wireless energy solutions as it can operate with very high conversion efficiency.
■eGaN® FETs have been previously demonstrated in a wireless energy transfer application using a voltage mode class-D topology [3, 4] and showed superior performance when compared to a system utilizing equivalent MOSFETs by as much as four percentage points higher peak conversion efficiency. At output power levels above 12 W, the design required a heatsink to provide additional cooling to the switching devices and gate driver. In addition, the traditional voltage mode class-D topology requires that the resonant coils be operated above resonance to appear inductive to the amplifier. This is needed to allow the amplifier to operate in the ZVS mode and overcome the COSS of the devices that would otherwise lead to high losses in the devices as opposed to being operated in the ZCS mode. Operating the coils above resonance comes at the cost of coil transfer efficiency and high losses associated with the matching inductor due to the presence of reactive energy.
■eGaN FETs have also been demonstrated in a class-E topology by Chen et al [5] with up to 25.6 W power delivered to the load while operating at 13.56 MHz. The wireless en-ergy transfer system was operated with very high load resistance (350 Ω) which ensured a high Q resonance, and the system efficiency was measured at 73.4% including gate power consumption. The shunt capacitor in that example was completely embedded in the EPC1010 device used in the experimental setup, thereby keeping the component count low.
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Technical Documentation |
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Please see the document for details |
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English Chinese Chinese and English Japanese |
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2017/06/16 |
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WP014 |
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5.8 MB |
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