本論文主要提出一雙模式控制返馳式轉換器(Dual-Mode Control
Flyback Conventer)控制電路，目的是使返馳式轉換器可同時操作在不
連續導通模式(Discontinuous Conduction Mode, DCM)和連續電流導
通模式(Continuous Conduction Mode, CCM)。操作在準諧振切換模式
返馳式轉換器之功率晶體，其導通時之切換損耗(Switching Loss)較傳
統返馳式轉換器低；但電路在準諧振切換模式下電感電流峰值較大，
此特性會造成功率級元件之導通損耗(Conduction Loss)增加，當負載
越重時損耗越大。連續導通模式下輸出二極體有逆向恢復時間，導致
一次側功率晶體在導通時之切換損耗增加，當負載越輕時操作頻率越
高此現象越明顯；但電路操作在此模式下電感電流峰值電流較小，此
特性使電路在重載時功率級元件之導通損耗較小。所以本論文提出一
新型控制電路，使返馳式轉換器在輕載時操作於準諧振切換模式，重
載時操作於連續導通模式，結合了上述兩個不同導通模式之優點，也
消除各自之缺點。

本論文先就兩導通模式之返馳式轉換器做損耗分析，計算出以輸
出功率200W 為設計條件時各個負載下之效率分布，因此可找出雙模
式控制返馳式轉換器的最佳轉態點。最後實際製作一200W 雙模式控
制返馳式轉換器，以實驗驗證論文中所提之分析與設計考量是否合
理。經測量結果證明，輕載下確實操作於不連續導通模式以減少切換
損耗；而重載下確實操作於連續導通模式以減少導通損耗。

The main purpose of this thesis is to propose a new control method for a
dual-mode control flyback converter. The presented flyback converter can be
operated under discontinuous conduction mode (DCM) at lighter loads, and
continuous conduction mode (CCM) at heavier loads. It is known that the turn-on
switching loss of a quasi-resonant (QR) flyback converter is lower than that of a traditional flyback converter. However, a higher peak inductor current is produced in a QR flyback converter. This will cause an increased conduction loss proportional to the load level in the power stage. The output diode suffers from a reverse recovery time under CCM operation, causing an increased turn-on switching loss at the primary side. This phenomenon is more obvious as the load gets lighter and the switching frequency gets higher. Nevertheless, the peak inductor current is lower under CCM. This results in a smaller conduction loss at heavier loads. A new control method is presented in this thesis to combine the advantages and to eliminate the disadvantages of these two modes. The flyback converter is operated under QR mode at light loads, while under CCM at heavy loads.

First, the loss distributions of the flyback converter at various load levels for both QR mode and CCM are analyzed. Therefore, a most suitable
transition point can be found to switch between the two operation modes. A 200-W dual-mode flyback converter prototype is built to verify the circuit analysis and design considerations. Experimental results show that the studied flyback converter actually operates under QR mode at light loads to reduce the switching loss, and under CCM at heavy loads to reduce the conduction loss.

[1] K. Harada and H. Sakamoto, “Switched snubber for high frequency
switching, ” in Proc. Power Electron. Spec.Conf ,pp.181-187,1990.
[2] C.P. Basso,“How to deal with leakage elements in flyback
converters, ” On Semiconductor, AN1679/D.
[3] M. Bildgen, “Resonant converter topologies, ”ST Microelectronics,
AN658/1194.
[4] K. Liu, R. Oruganti, and F. C. Lee, “Resonant switches topologies
and characteristics,” IEEE Trans. On Power Electronics, Vol. PE-2,
No.1, pp. 62-74,1987.
[5] V.Vorpe’rian,“Quasi-square-wave converters: topologies and
analysis,” IEEE Trans. On Power Electronics, Vol. 3, No.2, pp.
183-191,1998.
[6] E. Ismail and A. Sebzali,“A new class of quazi-square wave
resonant converters with ZCS,” IEEE . Applied Power Electronics
Specialists Conf., Vol. 1 and 2, pp. 1381-1387,1997.
[7] ST Microelectronics “Solution for designing a 400W fixed off-time
controlled PFC pre-regulator with the L6562A,” application note,
2008.
[8] Data Sheet, NCP1207A, NCP1207B “PWM current-mode controller
for free running quasi-resonant operation,” On Semiconductor, Nov,
2007 ,Rev. 8.
[9] ST Microelectronics, “ L6561, enhanced transition mode power
factor corrector,” Application Note, AN966, March. 2003.
[10] B.R.Lin, H.K.Chiang, C.E.Huang and K.C.Chen,“Analysis of an
active clamp forward converter,” IEEE PEDS 2005, pp.
140-145.
[11] 鄭玉南，「返馳式轉換器緩振電路研究」，國立台灣科技大學電
子工程系研究所碩士論文，民國92 年。
[12] 梁適安，「交換式電源供應器之理論與實務設計」，全華科技圖
書出版，民國93 年10 月。
[13] 原田耕介，新型柔性切換式電源技術入門，第一版，全華科技
圖書股份有限公司，1992 年。
[14] TDK Ferrite Cores for Power Supply and EMI/RFI Filter, 2007.
[15] 陳冠廷，「具功率因數修正器關閉功能之雙模式返馳式轉換器
研製」，國立台灣科技大學電子工程系研究所碩士論文，民國
99 年
[16] 陳宏安，「戶外交接箱饋電系統之研製」，國立台灣科技大學電
子工程系研究所碩士論文，民國98 年。
[17] P. Lidak,“ Implementing NCP1207 in QR 24W AC-DC converter
with synchronous rectifier,” On Semiconductor, AND8127/D.
[18] 林彥廷，「雙模式功率因數修正器之研製」，國立台灣科技大學
電子工程系研究所碩士論文，民國99 年。
[19] 黃健淳，「250W 局部零電壓切換準諧振升壓型功率因數修正器
之研製」，國立台灣科技大學電子工程系研究所碩士論文，民國
98 年。
[20] R.W. Erickson, D, Maksimovic, “ Fundamentals of Power
Electronics,” 2nd Edition, 2000.
[21] C.P. Basso, “SWITCH-MODE POWER SUPPLIES, SPICE
Simulations and Practical Designs,” 1st Edition, 2008.
[22] TDK Ferrite Cores in Switching Power Supplies,2007
[23] 林建宇，「雙模式升壓型功率因數修正器最佳化設計」，國立台
灣科技大學電子工程系研究所碩士論文，民國99 年。
[24] ST Microelectronics, “ L6561, POWER FACTOR CORRECTOR,”
Data Sheet, 2003.
[25] 劉宇晨，「700W 雙組輸出備援式直流直流轉換器研製」國立台
灣科技大學電子工程系研究所碩士論文，民國97 年。