| As the development of economy and progress of scientific, our society focuses more andmore attention on saving energy. Governments and industry associations make energystandards to conform to this trend. The laws and regulations to restrict the maximum power ofususlly consumer electronic devices in standby and load mode.Not only to save energy, butalso to satisfy relevant regulations, it is singnificant to make a study of reducing power loss.In this article, the system composition of flyback converter, working principle andswitching power loss were studied firstly. Then three modulation modes and peak currentcontrol modes of the switching power supply are analyzed. Compared with PWM, PFM hassmaller power losses under light load. The control signal shields off part of the clock cycleunder the BURST mode, which reduces power losses in standby. In order to reduce powerloss and improve transforming efficiency, a switch controller is designed based on muti-modeautomatic switching technology. The circuit is modularized according to the functional needsand design requirements, and every partial module of the circuit is separately designed andsimulated.The total circuit is simulated with the simulation software spectre of the tool Cadenceunder0.5um BCD process model. Simulation results show that the working mode of the chipis shifted according to the feedback voltage: When the VFB <0.4V,the chip works in cyclemode; When0.4V<VFB<1.2V, the chip works in PFM mode; When the VFB>1.2V, the chipworks in PWM mode. The simulation results verify the feasibility of the design and thecorrectness of the theory analysis and achieve the desired requirements. |
