The Control Circuit Design Of Quasi-resonant Primary-side-regulation Flyback Switching Power

Quasi-resonant primary-side-regulation flyback switching power has become a hot research topic of the flyback switching power supply because the utility model has the advantages of simple structure, low cost, low switching losses and low electromagnetic interference which buring from quasi-resonant technology. However, due to the time waiting for valley bottom which buring from quasi-resonant, the sampling error, the output cable resistance, the bus voltage and other factors, so that the accuracy of constant current and constant voltage are decreased. In this thesis, a new type of quasi-resonant primary-side-regulation flyback switching power supply control circuit is designed which works in quasi-resonant mode while maintaining a high constant current and constant voltage precision.In this thesis, firstly the principle of the primary side feedback and quasi resonant technique are analyzed, and some shortcomings of the current quasi-resonant primary-side-regulation flyback switching power supply are proposed. Then a complete set of quasi resonant primary side feedback switching power supply control method is presented. In constant voltage mode a2/3 of the demagnetization time sampling technology and chip built output cable compensation are used to improve the precision of constant voltage. In constant current mode a new boundary conduction quasi-resonant control method is used to solve the problem of the constant current precision decreasing caused by the time waiting for valley bottom. At the same time, the bus voltage compensation technology is integrated to improve the accuracy of the constant current under different bus voltage. Next, the design of the controller circuit and the simulation of each module are given this thesis. Finally, the system simulation is carried out in Saber and Cadence, which verify the feasibility of the control method and circuit given in this thesis.According to the results of simulation the design of quasi-resonant primary-side-regulation flyback switching power supply control circuit achieve the stable output of 5V-1A under the input voltage range of 90-220Vac. The accuracy of constant current and constant voltage is higher than 96%. And it also achieve precise valley switching which meet the design requirements.