A novel variable frequency modulation technique to improve light-load efficiency for multiphase synchronous rectified VRM

作者：Ou Sheng Yuan^*; Hsiao Ho Pu; Su Huei Fa

来源：International Journal of Circuit Theory and Applications, 2012, 40(11): 1085-1105.

DOI：10.1002/cta.773

• variable switching frequency modulation
• synchronous rectified
• multiphase interleaved control
• zero voltage switching
• VRM
• conduction loss analysis

A novel variable frequency modulation technique for multiphase synchronous rectified voltage regulator module (VRM) is proposed in this paper. The proposed technique provides zero voltage switching (ZVS) for high-side and low-side power switches under both light- and heavy-load conditions, thereby increasing the efficiency as compared to the conventional approach. The dependency of switching frequency on the load condition for the proposed modulation technique and the related conduction loss are analyzed. It will be shown that the frequency increases for light-load condition in order to retain ZVS and decrease the conduction loss. Although the switching loss will slightly increase due to the increase of switching frequency, the analysis and experimental results will show that the contribution of frequency increasing can cover this additional loss. Experimental results derived from a single-phase and an eight-phase synchronous rectified VRM show that the proposed modulation technique is superior to the conventional one and compared to conventional constant switching frequency techniques with 250 and 550thinspacekHz, the efficiency can be increased up to 17 and 5% for single-phase VRM and 8 and 4% for eight-phase VRM under various load conditions. Even an off-the-shelf controller with an additional simple and cheap control circuit comprising one switch, two operational amplifiers and several resistors is used to realize the proposed technique, that is, a very low cost and small circuitry is attached to gain the significant benefit.

• 出版日期2012-11