Contents Chinese abstract ………………………………Ⅰ English bstract…………………………………Ⅱ Acknowledgement…………………………………Ⅳ Contents……………………………………………Ⅴ List of Figures…………………………………Ⅷ Chapter 1 Introduction 1.1 Background and Review…………………………1 1.2 Key issues for LED driver IC…………………….2 1.3 Motivation………………………………………………………5 1.4 Market application and analysis………………………6 1.5 Thesis Organization……………………………………………8 1.6 References……………………………………………………9 Chapter 2 Basics of LED driver circuit 2.1 Introduction of LEDs…………………………………10 2.1.1 Characteristics of LED…………………………………10 2.1.2 Generation white-light with LEDs………………………11 2.2 Key words of optical sources………………………………12 2.3 White-light LED driver analysis…………………………13 2.3.1 Voltage modulation with RB mode………………………14 2.3.2 Current source with R B mode……………………………14 2.3.3 Multi-constant current of single channel mode……15 2.3.4 Constant current of boost voltage mode………………15 2.4 LED array………………………………………………………16 2.4.1 Matrix Circuit……………………………………………16 2.4.2 Series Circuit……………………………………………18 2.4.3 Matrix Circuit vs. Serial Circuit…………………19 2.5 LED backlight (3 series 7 parallel)…………………20 2.6 references…………………………………………………21 Chapter3 Principle of the boost converter 3.1 Introduction of power processing………………………22 3.2 Analysis of the ideal circuit…………………………24 3.2.1 Inductor current with switch closed………………25 3.2.2 Inductor current with switch open……………………26 3.2.3 The dc/dc transformer model……………………………29 3.2.4 Efficiency…………………………………………………29 3.3 Specifications and Definitions of LED Module Circuit..31 3.3.1 Power diodes………………………………………………32 3.3.2 Power MOSFET……………………………………………34 3.3.3 Capacitor…………………………………………………35 3.3.4 Layout method……………………………………………36 3.3.5 Application………………………………………………36 3.4 Load Regulation…………………………………………36 3.5 Line Regulation……………………………………………37 3.6 ESR of Output Capacitor……………………………………38 3.7 Noise………………………………………………………………40 3.8 Electro-Magnetic Interference (EMI)……………………40 3.9 Transient Response……………………………………………41 3.10 Protection Circuits…………………………………………41 3.11 Summary………………………………………………………43 3.12 references…………………………………………………44 Chapter4 Design and Analysis of the Circuits 4.1 Simulation Software…………………………………………………46 4.2 Single LED Model……………………………………………47 4.3 LED Driver Module……………………………………………49 4.4 Power stage……………………………………………………52 4.5 PWM control stage……………………………………………54 4.5.1 Error Amplifier IC (LM358)……………………………55 4.5.2 Comparator (NCS2200)……………………………………57 4.5.3 Voltage Control Oscillator (TLC555)……………………58 4.5.4 SR-Latch………………………………………………………60 4.6 PSpice simulation results……………………………………62 4.7 references………………………………………………………64 Chapter 5 Conclusions and Future Work 5.1 Experiment results…………………………………………65 5.2 The key issues for improving the efficiency……………67 5.3 Conclusion………………………………………………………68 5.4 Future Work……………………………………………………69 List of Figures Figure 1.1 The regulator bridges the PCB and the internal core circuits Figure 1.2 The traditional double charge pump converter Figure 1.3 Another type of charge pump converter (LinearLTC3210) Figure 1.4 Series type of the circuit structure (Linear LT3465) in LED array Figure 1.5 Series type of the circuit structure in LED array Figure 1.6 A schottky diode is used by the boost (step-up) converter transistor Figure 1.7 LEDs integrated into medical goggles worn by a substantial weight savings and fulfills the stringent requirements of high-quality color rendition required during medical operations Figure 1.8 Audi Corporation in 2004 using Lumileds Lighting’s Luxeon devices Figure 1.9 LEDs in large-scale display and signage applications continues unabated Figure 1.10 A seven-story high display and an animated pedestrian traffic signal Figure 1.11 The accent-lighted Stone Bridge across the Danube River located in Regensburg Figure 1.12 The flexible light piece by piece can use for marking paths and contours (ex. escape routes, borders and stairs) Figure 2.1 LED-based approaches for white sources including single-chip and multiple-chip, di-chromatic, tri-chroamtic, and tetra-chromatic approaches. Figure 2.2 The voltage source with R B mode Figure 2.3 The current sources with R B mode Figure 2.4 Multi-constant current of single channel mode Figure 2.5 Constant current of boost voltage mode Figure 2.6 The Matrix structure applies in LED array Figure 2.7 One LED fails in Matrix structure Figure 2.8 The Series structure applies in LED array Figure 2.9 One LED fails in Series structure Figure 2.10 The output current when the output voltage from 7V to 11V Figure 3.1 Three basic dc-dc converters Figure 3.2 The magnitude of v ripple (t) has been exaggerated Figure 3.3 The circuit of boost converter can be split into two parts Figure 3.4 When the switch is closed, the equivalent circuit that is applicable Figure 3.5 When the switch is open, the circuit that is applicable Figure 3.6 The waveforms of inductor voltage and inductor current Figure 3.7 The dc/dc transformer model Figure 3.8 The equivalent circuit model also allows us compute the converter efficiency η Figure 3.9 This is easier to do at low duty cycle, where D’ is close to unity, than at high duty cycle where D’ approaches zero Figure 3.10 Closing the switch causes current to build up through the inductor, as shown in the simplified LED driver module Figure 3.11 An LED driver module uses an on-chip MOSFET and PWM control circuit to perform the same functions as the simplified circuit Figure 3.12 Typical n-channel MOSFET static switch characteristics Figure 3.13 The effects of different ESR Figure 3.14 LED module vendors provide the domain of stability equivalent series resistance Figure 3.15 The characteristics of IOUT vs. VIN Figure 3.16 I-V curve of the LED module and the load line of a loading powered by this LED module Figure 4.1 The affordable, high-performance OrCAD product line is easily scalable with the full complement of Cadence Allegro PCB design solutions Figure 4.2 The process parameter of HT-U158BP’s data sheets Figure 4.3 Graph of forward voltage versus forward current for HT-U158BP Figure 4.4 Use HT-U158BP’s process parameter in PSpice to simulate ideal I-V curve Figure 4.5 Simulation result with external resistance of I-V curve by HT-U158BP Figure 4.6 Actual testing result of I-V curve by HT-U158BP Figure 4.7 A current-mode boost converter Figure 4.8 The PSpice’s schematic of power stage Figure 4.9 when frequency in 300 kHz, duty cycle is changed from 20% to 90%, the corresponding variations in output voltage Figure 4.10 when frequency in different value, duty cycle is changed from 20% to 90%, the corresponding variations in output voltage Figure 4.11 The analog-voltage control mode of PWM control circuit Figure 4.12 A differential pair circuits used by LM358 Figure 4.13 when RL in 2kΩ and 20kΩ is used, supply voltage versus voltage gain form Figure 4.14 when TA = 25°C is used, supply voltage versus input current form Figure 4.15 NCS2200 Series Supply Current versus Temperature Figure 4.16 NCS2200 Series Supply Current versus Supply Voltage Figure 4.17 NCS2200 Series Supply Current versus Output Transition Frequency Figure 4.18 NCS2200 Series Propagation Delay versus Temperature Figure 4.19 The PSpice’s schematic of TLC555 Figure 4.20 The results of PSpice simulation with TLC555 Figure 4.21 Power Supply Current versus Power Supply Voltage Figure 4.22 Input Bias Current versus Supply Voltage Figure 4.23 The SR-Latch of the circuit diagram Figure 4.24 Input signal of the SR-Latch Figure 4.25 The output voltage and current in PSpice simulation Figure 5.1 The testing board of LED array Figure 5.2 The output current versus time in testing board of LED array Figure 5.3 The specification of switching converter in general