The Design Of Solar Energy Harvest Circuit In Dim Lighting

IoT smart nodes are generally powered by batteries.For long-term applications,large-capacity batteries are required to ensure long-term stable operation and the application cost of the nodes will be increased obviously.The working life of the smart node can be extended by reducing the power consumption of the circuit node and supplementing the energy.Through the energy harvesting circuit,the smart node can be supplemented with energy during the entire working life cycle.Compared with other energy sources,solar energy has certain advantages in terms of power density and energy conversion efficiency.In order to enable the smart node to collect energy in dim lighting(usually when the light intensity is less than 200 lux),a solar energy harvesting circuit adapted to dim light conditions is designed.The basic principle and implementation method of energy harvesting in dim lighting is systematically elaborated.For the solar cell output characteristics,a dual comparator control method was used to stabilize the input voltage of the energy harvesting circuit at the maximum output power point of the solar cell.The output voltage of solar cell can be sampled by the sampling clock circuit and the input-voltage detection module.In order to realize the self-starting function of the energy harvesting circuit,a cold start circuit based on the multiplying charge pump was designed.In addition,the output signal of the input detection module is selected to conduct different numbers of power mos,which achieves the minimum sum of switching loss and conduction loss of the power tube under different input conditions.Finally,the hysteresis voltage regulation was used to control the stability of the output voltage and the secondary voltage.This design is implemented based on the GF130nm process with area of 0.25mm~2.The post-simulation results show that under the condition of TT process and ambient temperature of 27°C,the circuit can realize the self-starting function under the input voltage 200mV.After the circuit is started,the output voltage can be raised to 3V by continuous energy acquisition at the lowest input condition of 100mV,and the energy conversion efficiency can reach 49%.When the input voltage is 300 mV,the energy conversion efficiency can rise to 83%.