Research On Charge Management Circuit For Wireless Sensor Network Nodes

In recent years,the wireless sensor network has developed rapidly and has become the frontier and the hot spot of current research.Among them,the wireless sensor network has a large amount of nodes.They are maintained difficultly in the later period,and its own energy is limited,which greatly affects the service life of the wireless sensor network node.At the same time,the rapid development of portable electronic products has greatly promoted the development of power charging management technology.The application of efficient and low-power power supply management technology to wireless sensor network nodes can effectively solve the problem of low energy supply and short lifetime.This paper designs a Li-Ion battery charging management circuit based on the BOOST structure for the self-powered wireless sensor network node to charge its own energy storage battery.The chip has a high degree of integration.The power switch,the rectifier switch and the charge current limiting switch are all integrated in the chip,hance it can help to reduce the size of the power management system and the wireless sensor network node.The chip adopts TC-CC-CV charging mode technology: at the beginning,TC mode is used to activate the internal reactants in the battery;then,CC charging technology is used to shorten the charging time;after that the constant voltage charging is used to make sure that the reaction inside the battery will be completed.The chip also features high efficiency that is because the synchronous rectification technology is adopted.The synchronous rectification greatly reduces the loss caused by rectifier power switch,hence it improves the conversion efficiency of the system.In addition,when the chip operates in the TC mode,the PFM(Pulse Frequency Modulation)mode is used to adjust the system switch frequency.The combination of the PFM modulation mode and the PWM(Pulse Width Modulation)mode in the CC mode and the CV mode greatly improves the conversion efficiency of the chip.In terms of security protection,the chip has the function of protecting the temperature of the battery,hence it can ensure the safety of the battery and avoide the explosion and damage to the battery under high temperature conditions of the battery or low temperature conditions of the battery;it also has over-temperature protection,input over-voltage protection,input under-voltage protection,short circuit protection and charging time protection circuit.The overall simulation of the designed charge management circuit and the simulation of the main functional modules are performed.The technical specifications achieved are as follows: Improved bandgap reference circuit,the voltage deviation is only 871.9?V and the average temperature coefficient is 4.292ppm/°C in the temperature range of-40~+120°C.Charging current detection circuit in the trickle mode,the image charging current error is 0.2%;in the constant current charging mode,the image charging current error is 0.125%.The circuit has a high precision current mirroring capability.In the overall simulation,the TC(Trickle Current)-CC(Constant Current)-CV(Constant Voltage)charging process is verified.It is verified that in the TC mode,the chip system operates in the PFM mode,and the operating frequency is 260KHz;in the CC mode,the system operates at the PWM mode with the fixed frequency of 1MHz;in the CV mode,the system operating state changes from heavy load to light load.In terms of system conversion efficiency simulation,the conversion efficiency can reach 95.5% in CC mode and 94% in CV mode.The simulation results show that the charge management circuit designed for wireless sensor network nodes in this paper works normally and has high efficiency performance.