Design and Implementation of a Self-Dimming LED Driver With Pulse Width Modulation Feature

[[abstract]]本論文的LED (Light Emitting Diode)驅動電路主要以升壓式轉換器(Boost converter)、PWM(Pulse Width Modulation)技術、LED與系統控制 IC LT3761 建構而成。升壓式轉換器具有一個開關，其藉由電壓源與電感器組成的電流源輸入形式，經過開關的切換與低通濾波器濾波後，可產生大於輸入電壓源的輸出電壓。在本論文中，利用光敏電阻(Light Dependent Resistor)的特性，在環境光源越暗時電阻值會增加，反之光線較亮時，電阻值就會降低，藉此特性調變輸入控制 LT3761 IC的電壓，進而自動調控LED的亮度。在本研究實測過程中證實，藉著光敏電阻的特性與控制 IC內調光訊號產生器，來調變PWMOUT接腳的切換頻率，當照射光源愈亮時，其切換頻率愈小，反之，光源愈暗時，則切換頻率則愈大。因LED發光的強度與驅動電流的大小成正比，由此可得知，本論文的LED驅動電路，確實可以依照光源的強弱來調整輸出電流的大小，以達到節能的目的。[[abstract]]This thesis presents a driving circuit for light emitting diode (LED) which consists of a dc/dc converter and an auto-dimming mechanism Since it is connected to a lower voltage dc source a boost-type converter is employed to convert the lower voltage to required level This circuit utilizes IC LT3761 to achieve pulse-width modulation (PWM) feature of which pin assignment and function are introduced in this thesis The impedance of light dependent resistor increases with increasing light and vice versa Therefore LT3761 can automatically control the illuminance of LEDs according to a feedback signal determined by light dependent resistance The operation principle theoretical analysis and the control mechanism of the presented system are thoroughly described in this thesis Finally a prototype is built and tested to verify the correctness and feasibility of presented circui