Research And Design Of Constant Voltage Constant Current Buck DC-DC Converter With Average Current Mode Control

Under the premise of the rapid development of the power electronics industry,many applications such as LED modules have a strong demand for stable current or constant voltage.Based on the development status of LED drive power and charge IC and the challenges faced by power supply equipment suitable for these scenarios,combined with the requirements of power management,there is an urgent need for power chips or modules that can meet constant current drive or constant voltage output.The Buck DC-DC converter in the power management chip has the advantages of low power consumption,high efficiency,wide input voltage range,etc.,and can be used as an ideal choice for LED driving circuits or charging control circuits.This article first outlines the basic knowledge of the classification and working principle of the two circuits of LED drive power and charger IC.Taking constant voltage or constant current as the common starting point,the implementation of the two circuits is discussed,and the design goal of PWM step-down DC-DC converter is established.The circuit architecture,component characteristics,conduction mode and control method are expounded,and the design principle with average current mode control as the core is determined.Then,according to the circuit architecture of average current mode control,a new implementation method is proposed.The average inductor current is controlled by amplifying the error between the voltage difference on the internal resistance by the control current and the voltage difference on the sensing resistor by the average inductor current.The output current adjustment part is added to adjust the output current under the condition that the current maximum output limit is met,to adapt to the application requirements of different current sizes.When the chip drives high-power loads or high-current applications,the maximum current can be reduced in time according to the operating temperature to protect the load.In applications with temperature limitations,the output current can be reduced if the load temperature increases.Secondly,based on the prerequisites for the stability of the average current mode current loop,the gain extreme value of the error amplifier is determined,and the zero pole position of the loop after adding compensation is clarified.Finally,the chip system framework,pin functions and working principles are given,and peripheral circuits and application suggestions are given for some typical applications such as constant current LED driver and lithium ion battery constant current and constant voltage charging.The main design analyzes the bandgap reference,pre-conditioning circuit,error amplifier,oscillator and some protection circuits.The integrated step-down DC-DC converter chip XD2001B designed for constant current drive or constant voltage output is designed based on the above content.On the basis of the average current mode control,the regulation of output current is satisfied,and a certain amount of regulation accuracy is guaranteed.The precision design of internal control ensures a high output voltage regulation accuracy.The wide input and output voltage range can meet a variety of loads.Using external resistors to adjust the switching frequency or using external synchronization frequency can meet the needs.The parallel use of multiple chips can increase the output current without being limited by the different input voltages.Adding a variety of auxiliary circuits such as soft-start,overvoltage protection,overtemperature protection and current limit protection increases the chip’s safety performance.The chip is based on the 0.35μm BCD process,using the spectre simulation tool of the Cadence software platform to simulate the parameters and performance of some modules,and also to verify the overall circuit of the chip.The result can meet the predetermined 1.2V～24V output voltage range and 0A～12 A current control range,and the efficiency of various application scenarios can reach more than 90%.Realized the design requirements of efficient constant voltage and constant current.