Design Of Digital Multi-Mode Control With High Efficiency For Primary Side Flyback Converter

PSR flyback converter is widely popular in the field of medium and small-sized portable power adapter, for its advantages of low cost, high precision, high integration, high reusability and flexibility. In the background of increasingly scarce energy, improving the efficiency of power supply, especially the efficiency in the light load, has become the urgent request of power design now. Multi-mode control can choose different control modes according to the load status reasonably to improve the conversion efficiency. Therefore, digital multi-mode control design has been the hotspot in the power management chip design.A digital multi-mode (PWM/PFM/NPSM/DPFM) control adapted for the PSR flyback converter was designed in the thesis, which could improve the full-load range, especially the light-load conversion efficiency effectively. Firstly, the basic working principle of PSR flyback converter was introduced, and both the advantages and disadvantages of existing multi-mode control schemes were analyzed. Next, a NPSM control scheme adapted for the PSR flyback converter was designed, which could improve the light-load efficiency without the effect of audible noise. A detailed research on the output voltage ripple in NPSM control was carried out, and then the sources of system loss were modeled and analyzed. Based on the efficiency model, each function module of the digital multi-mode control was implemented, including the load range of segmented NPSM control, the switch of the multi-mode control and the adaptable valley switching. Finally, the overall design was simulated and tested in the prototype to verify its feasibility and validity.The result showed that, the digital multi-mode control design could achieve the basic functions of 5V/1A PSR flyback converter. Also, the accurate sampling, the stable switching of multi-mode and valley-switching were all realized. The constant voltage accuracy was ±0.9%, the output voltage ripple was below 90mV. What' more, the peak efficiency was 80.13%, the average efficiency was 79.54% and the efficiency of 10% load was 74.61% without audible noise, and the standby power consumption was no more than 47mW. The result mainly met the request of the thesis.