主動箝位之柔性切換返馳式轉換器之分析與實現

Analysis and Implementation of Soft Switching Flyback Converter with an Active Clamp Circuit

傳統的脈波寬度調變返馳式電源轉換器由於功率開關使用硬性切換，會產生嚴重的電磁干擾與轉換效率低的問題。本文研製一主動箝位之柔性切換返馳式轉換器架構，在傳統的脈波寬度調變返馳式轉換器增加主動箝位電路，使得主開關和輔助開關具有零電壓切換的優點，能有效地抑制開關上的電壓突波，減少切換損失，因此可以降低切換損失以提升轉換器的整體效率。根據主動箝位之柔性切換返馳式轉換器的電路狀態分析，在不連續導通模式 （DCM） 與連續導通模式 （CCM） 設計出諧振電容與臨界諧振電感的關係，使主動箝位之柔性切換返馳式轉換器操作在CCM 與DCM 時都能達到主開關與輔助開關零電壓切換。為了驗證本文所研製之電路架構的可行性，將實作一組輸入直流電壓為127~183 V，輸出電壓為24 V，輸出功率為120 W，操作頻率為50 kHz 之主動箝位之柔性切換返馳式轉換器。從實驗結果中得知，此主動箝位之柔性切換返馳式轉換器之效率在滿載的情況下可達到82.3%。

Traditional pulse-width-modulated (PWM) flyback converters sufferfrom serious electromagnetic interference (EMI) and have lower conversionefficiencies due to hard switching operations. This paper proposesa soft switching flyback converter with an active-clamp circuit. Anactive clamp circuit was added to the traditional PWM flyback converter,in order to achieve zero-voltage-switching (ZVS) at both the main andauxiliary switches. This design could reduce most of the switching lossand voltage spikes across the switches and improve the overall efficiencyof the converter. The boundary resonant inductor and capacitor were designed to achieve ZVS in both discontinuous conduction mode (DCM)and continuous conduction mode (CCM). The theoretical analysis of theproposed converter was verified using a prototype with the followingproperties: 120 W with DC 127~183 V input voltage, 24 V output voltage,and 50 kHz operated frequency. Based on the experimental results, theefficiency of the proposed soft switching flyback converter was approximately82.3% at rated output power.