改善USB產品待機轉換效率之直流降壓轉換器

Power Efficiency Improvement for USB Product in Suspend-Mode Using DC Buck Converter

蔡鴻璋(Hung-Chang Tsai)

指導教授 ： 宋國明

國立臺北科技大學/電資學院/電資碩士班/碩士(2011年)

https://doi.org/10.6841/NTUT.2011.00080

摘要

由於綠能科技的提倡，目前多數電子產品都具有待機模式，一些常見的電子規範甚至還有制定待機模式時最大功耗的規格，例如通用序列匯流排(USB)標準規範中規定待機模式電流限制必須在2.5mA以下。本論文提出一個可切換電壓轉換模式的直流降壓轉換器，以提昇待機模式時的轉換效率。一般電感型切換式降壓轉換器會在負載電流改變時，變換脈衝調變模式來提高轉換效率。藉由負載電流偵測器，電感型切換式降壓轉換器會在高電流負載時，使用脈衝寬度調變模式；在低電流負載時，使用脈衝頻率調變模式。雖然脈衝頻率調變模式在低電流負載時的轉換效率比脈衝寬度調變模式高，但是越低的電流負載，其轉換效率越低的情況卻是一樣的。當USB產品進入待機模式時，一般電感型切換式降壓轉換器的超低電流轉換效率往往不到20%。
本文提出一種可切換電壓轉換模式的架構：在待機模式時，電路會將切換式降壓模式改變成低壓降線性穩壓模式，並且針對USB產品的電流負載曲線，捨棄脈衝頻率調變模式，直接讓電壓轉換模式在脈衝寬度調變模式及低壓降線性穩壓模式之間切換。此電路架構不僅可以改善USB產品待機模式轉換效率，亦可達到縮短電路設計時間及節省電路晶片面積的目標。

關鍵字

脈衝寬度調變 ； 脈衝頻率調變 ； 低壓降線性穩壓 ； USB產品待機模式轉換效率

並列摘要

Because of the promotion of Green-Technology, all electronic products operate with the suspend-mode. Some specifications of common electronic product also have the rules about maximum power consumption in suspend-mode. For example of the Universal Serial Bus (USB); the specification requests the device just sinks maximum current 2.5mA from 5V bus power. A popular Buck Converter, changed with pulse width modulation, is used to improve power conversion efficiency when the load changes. In general, the popular Buck Converter uses the pulse width modulation (PWM) with the heavy current load, whereas the pulse frequency modulation (PFM) is used with light current load. Notify that the power conversion efficiency of PFM is better than that of PWM in light load. However, the conversion efficiency of Buck Converter is less than 20% when USB product works in suspend-mode.
In this thesis, we design a new Buck Converter with multi-operation mode to improve the power conversion efficiency in suspend-mode. That is, the Buck Converter changes in low dropout (LDO) mode when USB product operates in suspend-mode. According to the operational current waveform of USB product, it gives up the PFM mode, but switching between PWM mode and LDO mode. The proposed circuit can improve the conversion efficiency when USB product works in suspend-mode. The merit of the proposed structure not only speeds up the circuit design, but also reduces the chip size.

並列關鍵字

PWM ； PFM ； LDO ； power conversion efficiency ； suspend-mode

參考文獻

[2] H. W. Whittington, B. W. Flynn, D. E. Macpherson, “Switched Mode Power Supplies: Design and Construction,” Wiley, 1997.

[4] B. Wolbert, “Design with Low Dropout Voltage Regulators,” Micrel Semiconductor, 1998.

[5] George C. Chryssis, “High Frequency Switching Power Supplies: Theory and Design,” McGraw-Hill Companies, 1989.

[7] Phillip E. Allen and Douglas R. Holberg, “CMOS Analog Integrated Circuit Design,” oxford University, 2002.

[8] C. F. Lee and P. K. T. Mok, “A monolithic current-mode CMOS DC-DC converter with on-chip current-sensing technologies,” IEEE J. Solid-State Circuits, vol. 39, no. 1, pp. 3-14, Jan. 2004.