| With the development of times, because of the advantages such as high efficiency, small size, light weight and so on, switching power supply has been the main part of the power management ICs, and its market share is gradually expanding. The rapid development of electronic products especially portable electronics requires longer operating life of power supply. The technology of switching power supply needs to be improved to adapt to challenges.A kind of high power, synchronous step-down converter is designed in this paper. The converter can deliver up to3A output current from4.5V to23V input supply. It has the features of fixed340KHz switching frequency, output under voltage protection, over current protection and thermal shutdown protection. The converter is widely used in green electronics, computer peripherals, LCD monitors, TVs and so on.Under the design objective,the contens of peak current mode control and pulse width modulation are analysed in this paper, then system loop is established. Slop compensation is adopted to eliminate oscillations caused by peak current mode control. Chip peripheral components are designed according to loop stability, voltage ripple and current ripple. Then power switchs, delay of gate driving circuit, dead zone time control circuit, bootstrap circuit, level shifter and reverse current limitation of synchronous rectifiers are designed and simulated by HSPICE.System performances such as voltage ripple, current ripple, line regulation, protection, reverse current limitation of synchronous rectifiers are simulated with loop and submodules designed in previous chapters. The results show the system is well designed. |
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