| Integrated switching power supplies have been widely used in communication systems, computers, and consumer electronics etc. Motivated by portable applications that demand high performance, switching power supplies are developed mainly aiming to high efficiency, high precision and high integration.The primary circuit structure, basic principle and control methods of buck DC-DC converters are introduced firstly. Then each loss source of DC-DC converter is studied. New synchronous controllers according to different loads are proposed to do this job. Synchronous rectifying and soft-switching techniques are integrated skillfully, and decrease switching-loss effectively and increase the converter's conversion efficiency greatly. Also a new over-current protection circuit for DC-DC regulator is presented to protect the chip.In the practical design part, we start with the power stage, which includes the type and parameters selection of electronic devices, then a synchronous step-down DC-DC converter with PWM/PFM automatic switching is designed with 0.5μm CMOS process. According to the results of hspice simulation, the system is stable and other performance specifications required is attained.
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