The Design Of A Precision Primary-side Feedback Constant Current LED Driver Chip

In recent years, with the growing awareness o f environmental protection andsupport of national policy, LED lighting which is real environmental, low carbonemission and efficient develops very rapidly. Nowadays，because of the improvementof its manufacturing technology and the falling prices, LED’s future market isunlimited.Basing on many benefits such as broad market space, low carbon emission,environmental, etc., this paper designs a precision primary-side feedback constantcurrent LED driver chip to meet the demand for the driving power of LED lighting.Thedesign and tape out of this chip is based on CSMC0.25μm25V BCD Processtechnology platform.This chip is an offline constant current LED driver chip withhigh-precision. It can be used in LED constant current driving power, supporting fullinput voltage, AC85V~265V. The chip uses primary side feedback technology, whichcan realize constant current drive without secondary feedback. It also doesn’t needauxiliary transformer winding to supply power for the chip or detect the transformer’sdemagnetization. These methods greatly reduce the peripheral components and savethe cost as well as the size of the whole system. This chip integrates high precisioncurrent sensing circuit, which ensure the accuracy of LED’s output current within±3％, linear adjustment rate below3％, load adjustment rate within3％. Meanwhile itcan achieve more than80％conversion efficiency. This chip has perfect function ofprotection. It uses the time of transformer demagnetization to detect the outputovervoltage. The chip will enter the hiccup working state as soon as the overvoltagesignal is detected. This chip integrates the circuit which can detect output short circuitstate. It will working in lower frequency state to limit the output power as soon as theshort circuit signal is exported. In addition to all of the above, the protection functionof the chip also includes over-current protection of the transformer primary side, openor short circuit protection of the CS sensing resistance, under-voltage protection of thechip supply power, over-temperature protection, etc. All of these are aimed to ensurethe whole system working safely and reliably in harsh working environments.Against the design of this chip,the main work of this paper can be summarized asfollows: firstly,it introduces the design of this chip’s various functions on system level,in other words,the method of realizing each function of the chip.Secondly,it introduces the specific design and simulation of its each module. Finally, this paper gives the testresult of each parameter and functional. Now, the chip has been verified and enteredproduction phase.