Design Of Multi-Mode Quasi-Resonant Fly-back Switching Power Supply Controller

Recently, as the rapid development of information industry, modem switching power supplies are more and more widely applied to different electronic apparatus. And the higher performances are strongly requested for them, among which the high efficiency is one of importance. A high efficient power supply is helpful to heat dissipating and battery lifetime prolonging, which is critical for portable devices. Besides, it should be noticed that the worldwide trend for saving energy source also requires high efficiency of power supply. In face of the fact that huge amount of energy is wasted by the standby power of household electrical appliances and office devices, many countries have presented stricter laws to save energy source. The saving-energy guideline carried out in March 2006 by China allows 3W of standby power or less and 1.1 of efficiency index only. And the standby power of 1W or less and efficiency index of 0.75 or less will be carried out in March 2009 according to the guideline. All these challenge the future switch power supply design.Therefore, the thesis emphasized on the design of high efficient switch power supply controller, especially the improvement of the efficiency under light load condition. The working principles of fly-back topology power supplier, quasi-resonant technology and multi-mode control were fully investigated. And a novel multi-mode fly-back quasi-resonant controller was proposed. The controller adopted the quasi-resonant mode, frequency fold-back mode and burst mode respectively at different load condition to reduce its energy loss and improve its efficiency. And the quasi-resonant soft switch technique was applied to reduce switch loss.Up to now, a lot of efforts were put into the research on optimizing the switch power design and improving its efficiency. One approach is the soft switch technique that is used to reduce switch loss. And another way is so-called multi-mode control one that could hold high efficiency under all load conditions. The multi-mode means to use different control maneuver under different load conditions.The main innovation of the thesis is as follows. First, the complete structure of \ multi-mode quasi-resonant fly-back controller was proposed and developed and its operation principles were analyzed in details. Based on it, the complete circuit was designed. Some critical techniques were discussed and the solutions were given, which include multi-mode control, valley signal detecting, complex protection methods and so on.After completing the system design, all of the function blocks were designed using 1.5um BCD process. The circuit was simulated and verified by Cadence Specters. The results showed that all proposed functions were successfully achieved. The system using this controller was also simulated and verified. The performance of the system was consistent with expectation well.