Design And Realization Of Constant Voltage Loop For AC-DC Converter Based On Principle Of PSR

Switching Power Supply, which has a widely application in a great variety of electrical products and its terminal devices nowadays, have to meet new requirements of small size, light weight, and high efficiency for the"Green Energy"standard. Compared with the traditional one with photo-coupler feedback, the AC-DC converter based on the PSR(Primary Side Regulation) technology does not depend on the feedback loop in the secondary coil, then results in smaller size and lower cost of system and more convenient make and test. Referred to these advantages, it is of great significance for the study of this AC-DC converter based on the PSR technology.Therefore, firstly, the analysis of system operating principle is presented of this AC-DC converter. Functional modules are classified inside the converter chip. Then, external components and other parameters of this system are designed according to the defined technological parameters. Additionally, the loop characteristic of this converter based on PFM modulation is investigated, which leads to the mathematical expression of ideal logarithmic function for the generation of PFM-modulated signal with a satisfactory result of constant low-frequency loop gain in different cases of loads. Furthermore, transfer function of loop gain is obtained referred to the loop stability law, and that of error amplifier is made as well. An optimized curve of four successive segments is derived to approximate the ideal logarithmic function through the introduction of an error function, and is also realized in circuit by a method of switching capacitor with voltage feedback. For other sub-module circuits, the responding designs and simulations are also given. Finally, the defined specifications are verified through the total system simulations with related analysis and other discussion.