The Design And Realization Of A Low-power Ac-dc Chip

With the development of electric and electronic technology, the electric and electronic equipments have been used broadly in our work and life. Every electronic equipment can not work without reliable power. In 1990s the switching power had been used in all kinds of fields, such as exchanger, communication and control equipments. The core of switching power is control integrated circuits. Because it has the characteristics of high integration, most cost effective, simple periphery circuit and high efficiency. So it has been used broadly.The switching power supply unifies all kinds of advanced technology. It is suitable for high power AC-DC Adapters for Notebooks, Offline Battery Chargers, Set-Top Boxes Power Supplies, TV, Monitors, etc. Therefore the project is worth studying. A current-mode PWM switching power supply circuit is designed in this thesis. It is based on CSMC 1um 40VSPDMBiCMOS process. The system is controlled by current mode feedback loop on the basis of flyback topology. It is optimized for high performance low standby power and cost effective offline flyback converter applications in sub 10W range. It works at 50KHz frequency and maximum duty is 80 percent. Slope compensation maintains stability at duty more than 50 percent. Soft-start can eliminate the inrush current when the power switch starts. The chip itself goes into burst mode at light loads. Inter frequency jitter function is used for improved EMI. Over current,over voltage and over load protection are provided.This thesis first introduces the basic theory of current mode switching power. The operating theory of this circuit has been demonstrated. The operating principle and simulation analysis about UVLO, internal supply,gate driver, bandgap reference , current reference, voltage regulator, bias circuit, frequency jitter control, OSC, operating mode control, protection block, counter, logic and trim have been particularly expounded in the end of this thesis. Simulation results have declared the circuit function has been achieved and the performance characteristics have been obtained.This thesis then introduces the essences of BiCMOS process and layout. Some important devices'structure and layout are declared. The thesis also analyses layouts of some sub-circuits. At the same time, the whole layout of this chip has been provided and has passed the check of DRC and LVS.At last, the chip designed in this paper is summarized and the trend of this research is introduced.