Analyse And Design Of Isolated Switch Mode Power Supply Controller For Current Mode Control

Recently,like the growth of consumer electronic equipment,automobile using electricity or hybrid new energy have also begun to emerge.PMIC has become demanding.Current mode control and isolated power converters have many advantages,especially in distributed power system,which plays a very important role.In this paper,by using BCD process manufactured by Shanghai Huahong grace Semiconductor Manufacturing Co.Ltd,a chip is for an isolated power supply has been designed.In a typical application,input varies from 36 V to 76V(100V highest),while achieves 30 A output current.It has under voltage protection,over temperature protection,overcurrent protection and soft start function.Firstly,this paper analyzed switching power supply topology and its control strategy.Especially the active clamp forward topology and the PWM peak current mode,thus establishing the controller overall structure.Meanwhile,this paper also deduced the small signal model based on harmonic balance method.This small signal model can effectively avoid sub-harmonic oscillation,which is important for the design of the power supply loop.It enhances the performance of the converter.This paper also introduces the top-down design methodology.Comparing to the traditional design method,top-down design methodology can help make the design much more efficiency.It is also very helpful to find and solve problems effectively.Subsequently,this paper introduces the design of some of the key circuits of the chip,such as current generation circuit,PWM comparator circuit,high voltage regulator circuit and oscillator with pulse generation circuit.This paper analyzed these circuits theoretically and verified by circuit simulations(corner,AC and DC)Through this graduation project,the author has completed chip for peak current mode control and isolated switching mode power supply.Because of the ability of the author is limited,and many knowledge and understanding is not enough,the chip design still has some imperfect place,many function development is also limited,but the author believe that,soon or later,the PWM controller design will become more and more mature with much more functions.