A Current Limit Of Ac / Dc Converter Chip Design

Just like human's heart, power supply is indispensable in all kinds of electronic equipment. Switch power supply(SPS) is dominant in the power supply market because of its advantages in performance, size, price and efficiency. In recent years, with the enhanced awareness of environmental protection, most developed countries increase in demand for energy-saving gradually and develop standards about green power, so SPS is required to improve performance and reduce power consumption.Under the premise of researching PWM, PFM, voltage mode and current mode of SPS, an AC/DC IC with low power consumption and current limit control is designed in this dissertation. This IC integrates a power MOSFET with 700V blocking voltage. Its input voltage is 85VAC-265VAC and rated output power is 6W. This chip has many functions, such as current limit state machine, over-temperature protection, frequency jitter, leading edge blanking, auto-restart.In this dissertation, the development tendency of SPS was presented first. This dissertation then analyzed the PSM and current limit control of the chip, and described the operating principle, overall structure and application of the chip.In this paper, the author finished the analysis and design of some sub-circuit, such as bandgap reference, current limit state machine, over-temperature protection and auto-restart counter. Then the whole chip circuits were simulated with Hspice. The results indicated that the IC had achieved the design requirements, which demonstrates the excellent performance of chip in this dissertation.At the end of the dissertation, the layout of the sub-circuits and the whole-chip circuit and the test result of the chip were proposed.