Design And Research Of A High Efficiency Boost Charger

In recent years the demand for portable electronic device in consumer electronics market is increasing rapidly.Portable electronic devices such as mobile phones and laptops are indispensable in people's daily life.With the development of portable electronic device,consumers put forward higher performance requirements for the power supply system of the devices.To provide safe and reliable battery and power management for the devices has become an important concern of scholars.Based on this research background,a high efficiency lithium-ion battery charger chip was designed and studied to provide battery and power management solutions for portable electronic device.The service life of portable electronic devices is closely related to the service life of their batteries.Nowadays,with the lightweight development of portable electronic devices,most of the devices are powered by lithium-ion batteries with high energy density.However,in the process of charging lithium-ion batteries,overcharging and undercharging are easily occured to damage the batteries leading to the reducing of batteries capacity,the shorten of the equipment standby time and even battery explosion,resulting in safety accidents in the end.Therefore,prolonging battery life and improving the security of charging process have become one of the difficulties in the design of lithium-ion battery charger chip.In order to improve the battery charging efficiency and shorten the charging time,a Boost DC-DC converter to provide stable power supply and a battery charging management circuit were integrated together in this paper.Based on the consideration of the safety and reliability in the charging process,a three stage charging mode of trickle current/constant current/constant voltage was designed to charge lithium-ion batteries.At the beginning of charging,a low constant current is used to pre-charge the battery to activate the reactants inside the battery without causing the excessive temperature rise;with the continuous charging of the low current,the battery voltage gradually rises to the set trickle current/constant current switching threshold,at this time,the constant current charging mode will be used to increase the charging rate.But it is difficult to judge the stopping condition of constant current charging mode.Therefore,the constant current/constant voltage switching threshold is set before the battery voltage rises to the saturation value.At this time,the charging current decreases gradually,and finally the battery will be fully charged.For the design of Boost DC-DC converter,synchronous rectification technology was adopted,and the low-impedance NMOS power transistor was used to replace the rectifier diode to improve the convertion efficicency.In addition,in order to reduce the power consumption of the system within the full load range,the switching off time of the switch can be adjusted according to the load current of the Boost DC-DC converter by adaptive frequency reduction technology.In order to improve the reliability of the chip,a complete protection mechanism was introduced into the chip,which includes battery temperature protection,over-temperature protection,output short circuit protection,input current limiting protection and so on.The charging chip was designed and simulated in a 0.35 ?m BCD process of CSMC.The simulation results show that the chip has trickle current/constant current/constant voltage charging function and meets the design requirements.In the constant current charging stage,the conversion efficiency can be as high as 96.3%,and in the constant voltage charging stage,the conversion efficiency can be as high as 95.7%.