| With the development of electronics industry, DC-DC converters have been widely used in lots of electronic equipments. The power efficiency of DC-DC converter must be improved so that the lifetime of battery in portable electronic products can be prolonged.The primary circuit structure and basic principle of buck DC-DC converter are introduced firstly. Then the sources of power dissipation of DC-DC converter are discussed. The control methods of DC-DC converter such as pulse width modulation (PWM), pulse frequency modulation (PFM) and PWM/PFM hybrid control are analyzed together with their power efficiency. The result shows that PWM is high efficiency in high load and PFM is high efficiency in light load. So PWM/PFM automatic switching DC-DC converter is proposed to lower the power loss and improve the power efficiency. The switching is according to the variation of the load. The proposed system integrates summing mode PWM, skipping cycles and current limited PFM into one system. It makes the whole system works efficiently.The key circuits including reference, error amplifier, current feedback circuit, mixer, oscillator, and PWM/PFM selector etc. are designed and simulated with 0.5μm CMOS process. Finally, the whole system built with these circuits is simulated and debugged. The simulation results show that the system can work properly, PWM/PFM automatic switching is achieved. Its performance meets the design requirements. |
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