The Design Of A High-precision Non-isolated Constant Current LED Driver’s Chip

With the rapid development of China’s economy during these years, energy consumptions are largely increasing and the environmental pollution is becoming a major problem which plagues the country’s further development and improvement. As a result, energy conservation turns out to be an important research subject nowadays. Considering the fact that the lighting consumption accounts for 12% of the overall energy consumption, the implementation of energy-efficiency in lighting market is of great necessity-----LED lighting is acting such a role due to its low cost and high energy-efficiency, making it a prospective lighting technology in the future.For the reason that LED lighting has social benefits such as low carbon emission, environmental friendly, etc, it is believed to prevail in a broad market. This paper designs a high-precision non-isolated feedback constant current LED driver chip to meet the demand for the driving power of LED lighting. The design is based on CSMC 0.25um 25V BCD Process platform. This chip is a constant current LED driver chip with high-precision. It can be applied in LED constant current driving power, supporting full input voltage from AC85V to AC265V. The chip uses primary side feedback technology, which realizes constant current drive without secondary feedback, and there’s no need of auxiliary transformer winding to supply power for the chip or to detect the transformer’s demagnetization. This method greatly reduces the peripheral components and the cost as well as the size of the whole system. This chip integrates high precision current sensing circuit, which ensures the accuracy of LED’s output current within ±3%, linear adjustment rate below 3%, and load adjustment rate within 2%. Meanwhile it can achieve a conversion efficiency of more than 90%. This chip has a complete protection function and outputs the detection of overvoltage, which triggers the chip to work in the "hiccup" state, during the time of transformer demagnetization. It also integrates a circuit which can detect short-circuited output, in which situation the chip will work in a lower frequency to limit the output power. In addition, the protection function of the chip also includes overcurrent protection, open or short circuit protection of the CS sensing resistance, undervoltage protection of the chip supply power, over-temperature protection, etc. All of these are aimed to ensure the whole system working safely and reliably in harsh working environments.With regards to the design of this chip, the main work of this paper can be summarized as follows:firstly, it introduces the design of this chip’s various functions on system level and the method of realizing each function of the chip. Secondly, it introduces the specific design and simulation of every module. Finally, this paper gives the test result of every parameter and function.In the open-loop test, the starting current, starting voltage, working current are basically met the specifications, the clamping and brown voltage of VCC’s threshold point are basically agreement with the design value. Other parameters also meet the design requirements. In the closed-loop test, the line voltage regulation and load regulation of system are all within the scope of design requirements. Now, the chip has been verified and entered mass production phase...