The Research And Design Of LED Drive Circuit With Automatically Adjustable Current And Low-power

Known as the21st century "Energy Star" LED has been rapidly developing in recentyears. LED light source as a green and environmental friendly light, has advantages oflong life, high luminous efficiency, performance and stability, as well as multiple color,and its scope of application also continue to expand in the fields of LED display, LEDtraffic lights, LED indoor illumination, street lights architectural illumination, as well asautomotive lamps etc.Studies have shown that LED forward voltage has a great influenceon its forward current, mainly the voltage slightly change caused dramatic changes in thecurrent, The dramatic changes of current lead to thet rapid increase in heat release, islikely to burn out the LED and restricting the LED’s use and promotion of security andstability.Thereforer, constant voltage drive is not suitable for LED. Experiments showthat LED is a current driven device, the luminous intensity is determined by its forwardcurrent.Its performance stability is determined by its constant current.Therefore, in orderto play the LED as a new light source superiority, usually, LED need to have a specialconstant current chip in the course of its use and constant current chip performance has agreat influence on the LED promotional value. Especially in the field of high power LEDlighting, it need a higher demand to constant current chip. Therefore, stable performance,high integration, high conversion efficiency, cost-effective drive chip has a practicalsignificance to LED’s promotement simple peripheral circuit design drive on a widerange of applications of the LED has practical significance.In the view of requirements of over-temperature protection, overvoltage protection,long life, constant current output and low power requirements about LED drive circuits,this paper introduces a LED drive chip from the following three aspects:(1) The basic framework of the commonly used high-power LED driver chips wasanalyzed, as well as the problems in terms of constant-current,over-temperature,over-voltage be discussed in this paper. Based on the existing chip, the feasibility ofimproving the chip feature was explored.(2) In order to obtain the low-power and high-precision constant current output, inthis paper, constant current module is determined by using the operational amplifier andCMOS tube.the current mirror is designed by controlling CMOS tube’s drain with theoperational amplifier and operating in the linear region of the CMOS tubecommon-source, common-gate characteristics.It can achieve constant current module dual feedback, and make the power CMOS module can achieve low power consumptionand constant current output tube in the linear region.(3) In order to achieve over-temperature protection when the chip temperaturebecomes higher, this paper presents an automatically adjustable current programs.Theprogram makes over-temperature protection module into automatically adjust currentmode. Through the PN junction voltage changes to sense the change in temperature of thechip, then the changes of the PN junction voltage to control of the reference current,thenachieve the chip output current automatically adjustable.The design research of this paper has a reference value to LED drive circuit’sdevelopment.