A 10-MHz eGaN FETs based isolated class-Φ2 DCX

One of the challenge of multi-MHz resonant converters is to drive the power FETs efficiently in wide input voltage range, for the reason that the phase angle between the drain-to-source voltage and gate drive voltage of the power FETs varies with the input voltage. The phase angle variation results in high reverse conduction loss and switching loss seriously at high frequency, especially for the eGaN FETs due to the reverse conduction mechanism with the switching period of hundreds of ns. In this paper, it is interesting to find that if the output voltage is controlled to follow the input voltage proportionally, the phase angle remains fixed, so that the drain-to-source voltage and gate drive voltage of the power FETs matches well in wide input voltage range. Owing to the characteristics, the reverse conduction loss of the control FET and SR FET can be minimized. Therefore, a voltage following control method was proposed for the multi-MHz resonant converters. With this voltage following control, the reference voltage of the hysteresis control follows the input voltage proportionally to have the output voltage follow the input voltage proportionally, so that a DC Transformer (DCX) can be realized efficiently. An 18-24 V input, 18 W/ 2 A output, 10-MHz prototype of the DCX with eGaN FETs was built to verify the functionality and advantages.