Research Of DC-DC Constant Current Control Algorithm

With the purpose of reducing cost and improving practicality of the control circuit from the authorized China invention patent,this dissertation aims at integrating the involved modules including LED driving,battery charging,controlling and power management,on the premise of meeting LED constant current control and battery limiting current charge requirement.Firstly,according to the characteristics of Buck-Boost circuit,the LED constant current control algorithm characterized with fast dropping flow,precise adjustment and inefficient avoiding is designed based on analyzing the relationship between PWM and power convex function.On the one hand,this algorithm avoids the damage to device from current mutation caused by external factors,on the other hand it enhances the efficiency of power supply.Secondly,on the basis of the characteristics of Buck circuit,the battery limiting current charge algorithm characterized with step control is designed.While the batteries are being charged rapidly,the charging current is limited,which can effectively prolong the service life of batteries.At the same time,combined with the driving circuit,LED powering and battery charging are not happened all at once,which is promised to reduce the power requirements.Thirdly,the LPC1114 is configured through Keil ?Vision4 and ULINK2.By means of analyzing the relationships between voltage ripple and ADC resolution and well balancing the relationship between voltage ripple and PWM resolution,the related parameters are designed for reducing the influence of the voltage ripple to luminous efficiency and precision of LED constant current control.Fourthly,in order to ensure reliable operation of the modules and improve the effective utilization of the battery,the power management module jointly outputs and manages voltages needed of each module.Finally,by using the MOSFET driving circuit based on totem poles,the switching loss of MOSFET is reduced and the scope of frequency and power for circuit controlling is expanded;by adding a low bias voltage with high stability to the differential amplification circuit with single supply and single Op-Amp,the problem of minimum output voltage is effectively solved,which is conducive to accurate reading of sampling voltage and precise adjustment of PWM.The results of experiment show that the algorithm of LED constant current control and battery limiting current charge have fulfilled the DC-DC constant current control requirements and the module integration of LED drive module,battery charge module and other moduleshas achieved.