具動態頻率選擇器以改善效率之準諧振控制反馳式直流電壓轉換器

Abstract

在日常生活中的許多電器用品中，隔絕式的電源轉換器是不可或缺的。特別是反馳式轉換器，經常被選用於低瓦數的應用。而其中準諧振的控制方式，很常用在返馳式電壓轉換器上。為了使反馳式轉換器可以達到極高的效率，以及盡可能的縮小外部元件來符合綠色能源，此論文提出動態頻率選擇器的技術來改善效率，尤其是在負載較輕的情況下。此種轉換器將自動的切換在不連續導通的模式下。而且此種諧振形式的軟切換以能夠減少切換次數的頻率調變方式，可以將系統的切換能量損失減小到最低。此外，定電流啟動電路可以確保整體的低靜態功耗以便更進一步減少能量損失。另外，系統穩定度的問題當然也要嚴加考慮。只要在光耦合放大器上使用比例積分補償器即可確保系統在所有負載的條件下都可以穩定。此晶片使用0.5微米的500伏極高壓製程所實現，晶圓面積為3.6平方毫米。系統在一般負載的操作頻率是25千赫茲到125千赫茲之間，而在極輕載的狀況下頻率為2千赫茲左右。相較於傳統的控制法，在輸出為80瓦的時候整體效率的峰值可以達到92%，而輕載效率可達到85%。

For many electrical devices in our day life, a power supply with isolated converter is indispensable. Especially in low output power application the flyback converter is a better candidate. A quasi resonant (QR) control scheme is widely used in DC-DC flyback converters. To achieve a high efficiency flyback converter with minimized external components, this thesis proposes the dynamic frequency selector (DFS) technique to improve efficiency especially at light loads for green power. The converter automatically switches to the discontinuous conduction mode (DCM). The resonant type of soft switching and the frequency modulation for reducing switching frequency can minimize the switching power loss. Besides, low quiescent current can be guaranteed by the constant current startup (CCS) circuit to further reduce power loss. In addition, the system’s stability is also considered carefully. Utilizing the proportion integral (PI) compensator with opto-coupler amplifier can make sure the system is stable at all loads. The chip was fabricated by 0.5μm 500V UHV process occupied 3.6 mm2 active silicon area. The switching frequency can operate between 25 kHz to 125 kHz at normal loads, and about 2 kHz at ultra-light loads. The peak efficiency is 92% at load of 80W and 85% efficiency at light load of 5W.