本文旨在提出一種採用初級側電流循環電路之 LLC 串聯諧振轉換器，以 實現轉換器輕負載電壓調節之目的。該轉換器特點為電流循環電路於主動功率 開關切換瞬間，具有導引諧振電感電流於變壓器初級側產生迴流之功效。此作 法得以防止諧振電感對變壓器初級側繞組之寄生電容進行過度充電，進而次級 側繞組與輸出電容不致因此產生突波電流，且使得諧振轉換器所產生之輸出電 壓在輕負載狀況下能有效地維持在一定範圍內。最後，為確認所提轉換器工作 原理之可行性，本文實際研製一輸出規格為300 W/24 V 之電路原型機，實驗 結果證明所提出的方案可以有效且低成本的解決商用化的問題，不僅主動開關 切換所造成的突波下降、CISPR 22 Class B EMI 電磁干擾測試結果也令人滿意。

This paper presents a LLC series-resonant converter (LLC-SRC) with a primary side current-circulating circuit to enable light-load voltage regulation. The proposed converter topology utilized a current-circulating circuit to guide the resonant inductor current into the primary side circulation loop during the switching transient of active power switches. The parasitic capacitance of primary winding of the LLC-SRC was thereby prevented from resonating with the resonant inductor and from being overcharged. Thus, neither the secondary winding nor the output capacitor of the LLC-SRC would have spike currents, so as to effectively maintain output voltage of the LLC-SRC in a certain range when under a light load. Finally, a 300 W/24 V circuit prototype was implemented to verify its feasibility. The results showed that not only the voltage spike can be reduced, but also the performance of CISPR 22 Class B EMI test was satisfied.