本論文研製一架構簡單、高效率之低功率應用電源供應器，在不外加其他輕載控制策略的情況下可維持良好的輕載效率，重載效率也能達到相當的水準。前級電路架構採用簡單、易於實現之升壓型功率因數修正器，主要操作在邊界導通模式，開關有近似零電壓切換的效果，同時輸出二極體可達到零電流截止；而在輸入電壓零交越處則操作於不連續導通模式以減少切換損失。後級架構選用準諧振半橋轉換器，藉由固定操作頻率、調整開關責任週期的方式穩定輸出電壓。在上下橋開關同時截止之死區時間內，利用開關寄生電容與諧振電感諧振，在開關跨壓下降至相對低電壓波谷時導通；輕載時開關切換頻率固定，而非高頻操作，因此可有效抑制切換損失的增加；在輸出側另加入同步整流技術，降低導通損耗，提升整機效率。本篇論文實作電路規格為輸出功率90 W、輸入電壓90 ~ 264 Vac、輸出電壓19.5 V、滿載4.62 A，輕載(20%)時效率可達85%以上，整機最高效率可達92.61%。

This thesis studies and implements a simple, high-efficiency power supply for low-power applications. Without any additional light-load control strategies, the efficiency performances at both light and heavy loads are satisfactory. The front stage is a boost power factor corrector (PFC) operating mainly under critical conduction mode to fulfill near zero-voltage switching for the switch and zero-current switching for the output diode. Around zero crossings of the input voltage, the PFC operates under discontinuous conduction mode to reduce the switching loss. The post stage is a quasi-resonant half bridge (QRHB) converter. Since the switching frequency is fixed, the output voltage regulation is achieved by the duty cycle modulation. During the dead times, the switch parasitic capacitor and the resonant inductor form a resonant tank. The switch is turned on at a relatively low valley voltage. The switching frequency at light load remains constant, rather than goes high. These contribute to low switching losses. Moreover, the secondary synchronous rectifiers help reduce the conduction losses. A 90-W prototype circuit is implemented with universal input voltage and a rated 19.5-V/4.62-A output. The light-load (20%-load) efficiency reaches 85% and the peak efficiency can achieve 92.61%.

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