本論文利用氮化鎵功率元件研製一直流轉換器，電路架構使用具同步整流之主動箝位式順向轉換器。轉換器電路架構是採用低側主動箝位順向式電源轉換器，此電路可達到變壓器之磁通重置機制，回收變壓器漏電感能量，抑制開關元件電壓突波，並使開關元件達到零電壓切換，以減少開關元件之切換損失；再以同步整流電路降低導通損失提升效率。最後，實作一符合鐵道系統應用之直流電源轉換器，輸入電壓為43~160 V，滿載輸出5 V/20 A，切換頻率為300 kHz之電路，分析與討論以Si MOSFET與GaN FET為主開關之轉換器特性。實測結果顯示於60%負載時可達92.15%，滿載效率為90.5%。

In this thesis, a dc-to-dc converter using GaN power device is proposed. Active clamped forward technique is adopted in conjunction with synchronous rectification. The implementation of a low-side active clamp forward converter shows the ability to demagnetize the transformer, thus leading to the leakage inductance energy recovery, voltage surge suppression for switching devices, zero voltage switching realization; Additionally, the conduction loss is also reduced and improve efficiency due to the output synchronous rectification circuit. Finally, implement a dc to dc converter that meets the railway system applications specifications with an input voltage of 43~160 V, a full load output of 5 V/20 A, and a switching frequency of 300 kHz for a 100 W circuit in order to verify the result of proposed converter. The experimental results of GaN FET and Si MOSFET are also compared with power conversion efficiency. The experimental results reveal that the maximum efficiency is 92.15% at 60% load and the full load efficiency is 90.5%.

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