| Today,energy harvesting technology can collect electrical energy from many different types of environmental energy sources,such as solar energy,thermal energy,and vibration energy.In an ideal state,electronic equipment can run independently under the support of energy harvesting technology.Traditional IoT devices use lithium battery as the power source,which can meet most applications,but the limited capacity of the battery is always difficult to meet the user’s requirements for battery life.Traditional IoT devices use lithium battery as the power source,which can meet most applications,and the limited energy density of the battery is always difficult to meet the requirements for battery life.The energy harvesting technology can be used to charge the battery of IoT devices to extend battery life.Because the output power of the transducer is unstable,a complete energy harvesting system must include a charge and discharge management circuit to ensure that the charge and discharge process is safe and controllable.This paper proposes a lithium battery charge and discharge management system for energy harvesting.The proposed battery management system consists of three main building blocks: a pulse charger,an adaptive boost converter,and a power path controller.The pulse charger can work in a variety of charging modes,such as trickle mode,fixed frequency fast charging mode,fixed frequency slow charging mode and variable frequency charging mode.The built-in resistance compensation technology under pulse charging technology is proposed to speed up the charging time of a lithium battery.Pulse charging can eliminate concentration polarization,help the effective diffusion of lithium ions,and extend battery life.Adopt fast charge(75% duty cycle)and slow charge(25% duty cycle)to adapt to the characteristics of lithium batteries in different stages;The power path controller is used to control the power path and cooperate with pulse charger to select the optimal charging path.It can help the charging circuit to work better in the energy harvesting scenario.An adaptive boost converter that provides a power rail for a lithium battery charging circuit is designed for practical needs.It can convert an input voltage within a certain range to the power supply voltage required by the charging circuit,and the output voltage dynamically tracks the battery voltage of the lithium battery to minimize losses on the charging path.The lithium battery charge and discharge management circuit is implemented on a 0.18 μm CMOS technology process.This design is performed in two stages.In the first stage,the adaptive front-stage boost converter is designed.The input voltage range is 1.5V-2.5V,the output voltage range is 3.2V-4.7V,the switching frequency is 1MHz,and the maximum load current is 300 mA.In the second stage,the charging circuit and power path controller are designed.The system can charge lithium batteries with a maximum capacity of 300 mAh at a rate of 1C,a charging termination voltage of 4.2V,and a maximum compensation resistance of 200mΩ. |
