Dual Modulation Technique for High Efficiency in High-switching Buck Converters Over a Wide Load Range

• Main Authors: Huang, Tsung-Ying, 黃琮瑛
• Other Authors: Chen, Ke-Horng
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/94546776259846184595

碩士 === 國立交通大學 === 電控工程研究所 === 99 === For today’s portable electronic device applications, high performance and compact size voltage regulator plays an important role to provide system power. To reduce the size of output filter, a high switching dc-dc buck converter is presented to achieve high integration. However, the conventional current mode DC-DC buck converter is not suitable for high switching operation, because the system conversion efficiency deceases drastically at light load condition and the operational amplifiers of control circuits restrict system’s bandwidth. That is to say, the drop of the efficiency at light load makes the converter not suitable for commercial application and the limitation of circuit bandwidth causes incorrect operation at a high switching frequency. To solve these issues mentioned above, the dual modulation technique is presented in this thesis. Owing the dual modulation technique, the AC ripple detector in primary modulator not only makes converter operate at a high switching frequency correctly but also speeds up the transient response, and the hopping switching pulse produced by secondary modulator reduces switching times of power switches to raise efficiency at the light load condition. In this thesis, a dual modulation technique to improve power conversion efficiency with minimal increase in output voltage ripple is presented. The worsening switching noise caused by parasitic resistance and inductance due to high-switching operation can also be alleviated by the proposed AC ripple detector. Furthermore, the dual modulation method can speed up the load transient response since the switching frequency can increase to 10 MHz during the transient period. At very light loads, the switching frequency is always kept higher than the acoustic frequency to avoid noisy sound. Experiment results show that the converter operates at 5MHz using a small inductor of 1μH. The load transient response time is shorter than 3μs when load current changes from 150 to 450mA or vice versa. Power efficiency is kept higher than 85% over a wide load current range. Specifically, light efficiency can be raised to about 45% above that of the conventional design.