A Design Of Costant Current LED Driver Based On COT Technology

As a novel and efficient green lighting product, LED lighting attracts widespreadattention with the advantages of environmental protection, energy saving, and highluminous efficiency. Current banning on the import and sale of general lightingincandescent lamps provides an excellent opportunity for LED lighting to penetrate thegeneral lighting market. With the wide application of LED lighting devices, LED driverchip, the core components of LED drivers, draws more and more attention. LED driverare developing towards the directions of high efficiency, small size, high reliability, highpower factor, high-accuracy current, rapid dimming, highly integrated density, long-lifeand intelligent control. And also the system architecture is gradually developing towardsthe direction of the single-stage architecture.This thesis talks about a constant current LED driver chip based on the technologyof COT (constant on-time).This chip is designed with the characteristics of a wide inputvoltage range (6V to54V), high efficiency, high integration, high reliability, small size.This chip is also integrated a1.6A power NMOS. To improve the reliability of thesystem, this chip has integrated several modules with the functions of powerunder-voltage protection, power MOS under-voltage for gate-to-source voltage,over-temperature protection, over-current protection, and power MOS current protectionwith high-end sampling.In this thesis, first, the basic characteristics and drive mode of high-power LED areintroduced, especially introducing the Buck constant current LED driver based on thehysterestic control mode and the COT control mode. Considering the indicators of thechip, the Buck constant current LED driver based on COT control mode is the bestchoice, at the sane time the hysteretic control mode as a protective mode of this chip.Then, the thesis explains the principle of the LED driver circuit based on COT mode. Inaddition, some important sub-module circuit based on0.25μm60V BCD process in thechip are analyzed and simulated. The simulation results of the whole circuit are showedthat the average output current is700mA, and the output current ripple is80mA whichis11%of the average output current, and the efficiency can reach98.4%. According to the simulation results, it is that the chip’s performance and functionality meet all thedesign requirements.This thesis describes the BCD process and layout design of this chip, andelaborates some layout problems that need attention in the core circuit. Then, accordingto the test results of this chip, this thesis gives the failure analysis of this chip and someeffective improvement measures.