| With the fast development of information technology as well as the establishment of the Web of things based on big data,it is easy for people to obtain required information and control equipment with a personal terminal.Being the most popular and the most representative one,cellphone has experienced more than 20 years development since the first smart phone IBM Simon appeared in 1993,and it has been an indispensable equipment for us to deal with various kinds of things.At the same time,with the number of functions becomes more and more,the size of screen becomes larger and larger,endurance of batteries is given increasing concerns.While,limited by the Lithium-ion battery technology,it is hard to abidingly enlarge the capacity of battery with the restrain of a small volume.Generally,the adaptor that composed of constant current constant voltage(CC-CV)AC-DC converter usually characterized by a constant current control accuracy about ±5%,and has a maximum output power of less than 5W(5V/1A)with the transfer efficiency less than 73%.Such poor performance of the traditional CC-CV converter system does harm to the battery and leads to a long charging time as well as an obvious heating of the adaptor.In this condition,to research quick-charge technique that characterized by high constant current control accuracy of ±2%,high transfer efficiency of more than 80% and large output power of more than 5W are of great importance,and focused researches are made in this dissertation to solve these problems.Generally,a mobile phone adaptor is composed of a AC-DC converter system.Focused on a typical PSR Flyback AC-DC converter system,which can be divided into three states when operation,they are start-up state,constant current output state and constant voltage state.As to each state,there are some drawbacks,such as large quiescent current during start-up state,low accuracy of current output in constant current output state and low transfer efficiency when constant voltage state.To overcome the problems mentioned above,corresponding strategies are proposed in this dissertation after research,they are,1.A high precision constant current control method is proposed.Nowadays,portable device charging system and LED driver call for high precision output current,and an inaccurate charging current does harm to the safety as well as the lifetime of portable devices.For the control precision of existing constant current control technique rely on the stability of process,in this dissertation,a novel knee point detection method is proposed to dilute the influence of the variation of process.Firstly,sensing and amplifying the ripple of auxiliary voltage with a capacitor amplifier,then making a comparison with given threshold voltages,when the amplified ripple voltage lies between the threshold voltages for a certain time,a pulse is generated and signifies the knee point is detected.In this way,the accuracy of output current can reach a level as high as ±0.8% and has nothing to do with the process.2.A power stage model of a Flyback converter system is established based on steady state method.To deduce the power loss of a Flyback converter system and satisfy the latest Do E.6 energy standard,a power stage model is derived after researching the loss mechanism of each part of the system,making the model suits for engineering application compared with these partial or excessive complicated models.The model proposed contains the factors such as switching frequency,primary side sensing resistor,primary side peak current,ratio of Flyback transformer,secondary rectifier diode and the like,which making the model able to give a comprehensive reflection of both quiescent loss and switching loss of a converter system,providing the theoretical bases of low power loss as well as high efficiency design.3.An optimized constant voltage control technique is proposed to improve the transfer efficiency.According to the model derived previously,simulation and analyzation are made to find the power loss and the variation tendency of different factors,after that the proportions the total of different loss factors can be obtained.Based on which,control curves of these factors can be determined.Simulation as well as testing results show that,by adopting the mentioned control strategy,the average transfer efficiency of the Flyback converter system at 0.5A,1A,1.5A as well as 2A load conditions can reach a level as high as 84.7% at 5V/1A output.4.A gain adjustable high precision load current sensing circuit is proposed to recognize the current protocol.The sensing circuit characterized by a high symmetric structure and consists of two kinds of feedback loops,they are common mode negative feedback loop and differential mode positive feedback loop.By this means,the error aroused by process can be well restrained,and the amplification time of small signal is adjustable and quite stable,more over,the detection resolution can as low as 5m V.The proposed circuit is realized in a 30 V BCD process,simulation and testing results verify that the detection error with temperature range from-40° to 125° is less than ±3% at all corners.5.An ultra-low operating current under voltage detection circuit with high precision is derived to reduce the quiescent power loss in start-up process.The circuit is designed based on subthreshold and bandgap theory,and the working sequence of this block is not lag behand the bandgap circuit,hence,the operating current is greatly decreased.Experimental results verify that the operating current of the proposed circuit is less than1 u A,the detection accuracy is within 1V.So that,the problem of quiescent power loss is well resolved. |
