| Portable power is increasingly becoming the most important application area for power semiconductor integrated circuits (ICs). Small form factor, high efficiency and low cost are the most desired features for portable power ICs. This paper focuses on the conversion efficiency of DC-DC boost converter, which must be improved so that the lifetime of battery in portable electronic products can be prolonged. The method, implementation and optimization will be discussed.The primary circuit structure and basic principle of boost converter are introduced firstly. Then the sources of power dissipation of DC-DC converter are discussed and modeled. The relationship between the system efficiency and load current is derived, as well as frequency. It shows that the efficiency becomes better in PFM (Pulse frequency modulation) mode than in PWM (Pulse width modulation) mode under light load. So the PFM/PWM hybrid mode is proposed to realize the high efficiency in a wide load range. The PFM/PWM control logic circuit is designed, by which the system can operate in PWM when driving medium to heavy load and automatically switches to PFM mode if the load required less power. The optimized methods of the primary dissipated sources are discussed, such as power transistors, driver circuit and synchronous rectifier.The boost converter is designed and simulated based on 0.6um BiCMOS process. Finally, the full system is simulated and debugged. The simulation results show that the system not only can work properly, but also have high efficiency in full load range.
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