Design Of High Precisely Constant Current Controller XD1102Based On Fly-back Primary Side Feedback

In recent years, more and more attention has been paid to power managementprojects with high performance, low cost and small scale with the popularization andrapid growth of portable electronic products. The paper is based on the key project“Theoretical Research and Design of Key Technique for Power Management IC” of theinstitute of High Speed Circuit Design in xidian university. In the project, the workingprinciple of fly-back converter based on the primary side feedback control is analyzedand a high precision constant output current control IC XD1102for fly-back converteris designed.Firstly, a brief introduction is given to the development history, present conditionand prospect in switch-mode power supply, as well as the basic working principle of it.Then based on the introduction the basic structure and working principle of the fly-backconverter, together with the characteristics of different control methods are introducedin detail. And a new type of feedback control method which is the primary sidefeedback is introduced for fly-back converter. In addition, the system circuit structure isresearched and designed, main electrical characteristics are set and the system stabilityis analyzed according to the function and characteristics of the IC. Afterward, the designand simulation of key sub-circuits are presented such as power supply, voltage reference,discharge time detect, output current calculation, error amplifier, oscillator etc. Finally,the typical application circuits and simulation results of the whole chip are given.XD1102controls the output current precisely with the information on the primaryside which can not only remove the output current sensing loss but also eliminate allsecondary feedback circuit resulting in simple application circuit, with reduced cost andhigh efficiency. The normal working frequency of the IC is42kHz and the maximimumduty cycle of the output signal is80%with the precision of output current control up to10%. At the mean time, some protection circuits are intergrated such as under voltageprotection, over voltage protection, over current protection, making the system safe andreliable.