Multi-mode controller IC for soft-switched flyback converter with high efficiency over the entire load range

• Published in: Journal of Zhejiang University. A. Science Vol. 9; no. 10; pp. 1411 - 1419
• Main Authors: Chen, Hai, Zhao, Meng-lian, Wu, Xiao-bo, Yan, Xiao-lang
• Format: Journal Article
• Language: English
• Published: Hangzhou Zhejiang University Press 01.10.2008; Institute of VLSI Design, Zhejiang University, Hangzhou 310027, China
• Subjects: Civil Engineering; Classical and Continuum Physics; Engineering; Industrial Chemistry/Chemical Engineering; Mechanical Engineering; 回扫转换器; 多模控制器; 检测方法; 集成电路; Multi-mode controller; A; Valley detection; Integrated circuit; TN4; Soft-switched flyback converter; TN86
• ISSN: 1673-565X; 1862-1775
• DOI: 10.1631/jzus.A0820142

This paper presents a multi-mode control scheme for a soft-switched flyback converter to achieve high efficiency and excellent load regulation over the entire load range. At heavy load, critical conduction mode with valley switching （CCMVS） is employed to realize soft switching so as to reduce turn-on loss of power switch as well as conducted electromagnetic interference （EMI）. At light load, the converter operates in discontinuous conduction mode （DCM） with valley switching and adaptive off-time control （AOT） to limit the switching frequency range and maintain load regulation. At extremely light load or in standby mode, burst mode operation is adopted to provide low power consumption through reducing both switching frequency and static power dissipation of the controller. The multi-mode control is implemented by an oscillator whose pulse duration is adjusted by output feedback. An accurate valley switching control circuit guarantees the minimum turn-on voltage drop of power switch. The prototype of the controller IC was fabricated in a 1.5-μm BiCMOS process and applied to a 310 V/20 V, 90 W flyback DC/DC converter circuitry. Experimental results showed that all expected functions were realized successfully. The flyback converter achieved a high efficiency of over 80% from full load down to 2.5 W, with the maximum reaching 88.8%, while the total power consumption in standby mode was about 300 mW.