Analysis And Application Of Active Clamped Forward Converters

With the rapid development of society and constant improvement of the electric,a variety of and electrical equipment appeared.Switching power supply,a kind of power electronic equipment,plays a significant and irreplaceable role in various fields such as the industrial automation control,the military equipment,the medical equipment,the instruments and apparatus,and digital products.In order to meet the characteristics of small size,large power and strong stability of modem power electronic equipment,the development of switching power supply tends to be lightweight and high frequency.However,the switching losses of semiconductor components are directly proportional to the switching frequency.The higher the switching frequency is,the greater the loss,and the lower the efficiency.In order to solve the above problems,the main contents of this thesis are as follows:(1)A new type of soft switching technology is proposed to overcome the disadvantage of increased switching losses due to the increase of switching frequency.The design does not increase the complexity of the whole circuit,but effectively inhibits the conduction loss of the primary side,and realizes switch tube ZVS(Zero-voltage-switching)conduction.The efficiency of the whole machine is improved,and the switching loss and electromagnetic interference are reduced.(2)In view of the problem that the core of the forward circuit transformer can not be reset automatically,the active clamp forward circuit topology is proposed.The main method of implementation is to add a branch on the basis of the traditional converter,which is connected with clamping switches and capacitors in series.This method can not only complete the magnetic reset effectively,but also make the transformer work in an efficient one or three quadrant so as to improve the efficiency of the whole system.(3)According to the working principle of active clamp forward converter,the working cycle is divided into seven stages,and on the basis of which,the physical design scheme is summed up.Then a prototype of 50W is built and simulated by PSPICE.The simulation results verify the rationality and accuracy of the design.At last,on the basis of theoretical analysis and circuit simulation,a switching power supply with LM5025 as control chip,operating range of 18V-75V,output voltage rating of 5V,output current of 20A,and working frequency of 200KHZ,all the performance indexes of the finished product conform to the design requirements.The experimental results show that the switching loss is significantly reduced and the efficiency is improved by 2%-3%compared with hard switching.Secondly,under different voltage input,the efficiency curve is basically consistent and output is stable.Finally,by active clamping,the core reset can be performed perfectly.To sum up,the research content described in this paper has high superiority and practical engineering significance.