| Due to the portability and easy to use characteristics, digital cameras are more and more popular in our daily life. It is capable to faithfully record the most precious and beautiful moment for everyone, so it becomes an essential part in our life. The target of this paper is to design a switching mode DC-DC boost convertor for a digital camera application. It could be used as the power of lens control, automatic focus and shuttle control circuitry.Since the design is for digital camera application, the DC-DC boost convertor need to be capable for a wide range of input voltage, to produce stable output voltage and relative high output current capability. To achieve the high efficiency, it was a PWM (Pulse Width Modulation) based Boost converter, using voltage control mode and the switching frequency could be adjusted basing on the application requirement. SMSP (Switch Mode Power Supply) was called as high efficiency & power saving power supply in the industry. It presents the developing direction of power supplies. And now, it has been the most popular product in the electrical market. When it works, Switching power MOSFET is in the high frequency switching mode, so the equivalent resistance is very low. If the high current flows through the switching power MOSFET, the power dissipation on this power MOSFET is very low. So the SMSP could achieve high power efficiency, sometimes nearly one time higher than normal linear power supply. SMSP has many advantages like high integrated rate, simple peripheral circuitry, high power efficiency, etc. It was widely used in various electrical products, especially in the battery powered handset systems. SMSP has already become the very important part of modern complex electronic system.DC-DC Boost converter in this paper contains several sub-modules, like band-gap module, saw wave generator module, over current protection module, error amplifier module, etc. To meet digital camera application requirement, the design target of Boost DC-DC convertor are listed here: Input voltage from 4V to 12V, output voltage is designed to be 20V. The maximum continuous load current is 150mA. The over voltage protection threshold is set to be 110%*output voltage; while the short circuit protection threshold is set to be 90%*output voltage. The soft start time will be no longer than 5ms and the over current protection current will be in the range of 1.4A~2.4A. This DC-DC convertor will be designed under Freescale advanced 0.28um CMOS Fab technology.In this paper, the first chapter introduces the basic knowledge of SMPS, its history and developing direction. And then it explains DC-DC switching power supply principles in detail, including the basic topologies of DC-DC convertors, switching modulation methodology and feedback control modes, etc. Following with this knowledge, this paper clearly describes the design target and specific parameters, including the top level circuit topology and analysis for each sub-module. Then Cadence simulation tool was used to simulate and analyze the design target and parameter. As the end chapter of the paper, it analyzed and compared the lab test results and waveforms with automatic real test data from the final product. |
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