Mathematical And Physical Model And Characteristics Of In GaN/GaN Light-emitting Diode And Its Optimal Drive Current

Indium gallium nitride (InGaN) and gallium nitride (GaN) based white lightemitting diode (LED) luminaire system presents a pathway to alleviate the energy crisisfacing the whole world. Research and exploration of the electrical, optical and thermalcharacteristics of the LED play a critical role to enhance feasibility, reliability andefficacy for LED lighting, therefore it is significant to the development of the solid statelighting industry.InGaN/GaN LED is an optoelectronic device converting the electrical energy tolight and exhibits complex characteristics. After analyzing the typical LED lightingsystem, the characteristics are extraordinarily complicated, especially by pulse-widthmodulation (PWM) waveform to drive the LED. With the experimental study andmodeling analysis, an understanding of LED characteristics and its mechanism can beenhanced, which provides an important experimental and theoretical guidance to theoptimal design of LED package and its current drive.To solve the weakness of commercial LED test system in measuring the electro-optical and thermal coupling characteristics, the key units including the digital currentsource, temperature controller, and PWM current-driver are developed, and they havebeen integrated into the commercial system by virtual instrument software to improvethe performances of the test platform. Moreover, the basic principles and methods ofexperiments are discussed. All these efforts provide the hardware support and methodguidance for the experimental study of the characteristics of InGaN/GaN LED.For an in-depth study of the electro-opto-thermal coupling effect in InGaN/GaNLED applications, numerous experimental, modeling and analysis studies of InGaN/GaN LEDs have been carried out according to the built platform, and the parameterextraction algorithms for the mathematical physics model and their accuracy have beenaddressed, furthermore, the improved algorithms are reported. Additionally, thecharacteristics and laws of the quantities for the InGaN/GaN LED are obtained, whichprovides a reference to understand microscopic mechanism and optimize the design.In order to obtain the microscopic understandings on the InGaN/GaN LEDcharacteristics, the collected data and their features of the single-chip LED have beeninvestigated according to the LED material properties, the package structures and thecarrier transports. The results can benefit the microscopic interpretations on InGaN/GaN LED light output decay and improvements of InGaN/GaN LED studies in the wholefabrication chain.For meeting the demand for multi-chips InGaN/GaN LED characteristics inhigh-power lighting applications, the mathematical and physical modeling on electro-opto-thermal characteristics of multi-chips LEDs has been conducted based on that ofthe single-chip LED, and the model parameters optimization process is given.Furthermore, a novel multi-chips on board (COB) package method is proposed, and an9-chips module prototype and its characteristics are demonstrated, which provides thetheoretical and practical guidance for the design and development of high powerInGaN/GaN LED.Focusing on parameters of drive current on InGaN/GaN LED, a simplifiedcurrent-light output model involving the electro-opto-thermal coupling characteristics ofsingle-chip LED has been derived from the experimental study and modeling of thecharacteristics. Furthermore, the drive currents at a quantitative and the maximum lightoutput have been obtained from the model, additionally; an optimization controlprinciple of the driving current is suggested combining the constraint of the estimatedlifetime. The results provide an important theoretical guidance for the InGaN/GaN LEDdriver design.To reduce junction temperature measurement complexity in the optimum currentdrive for multi-chips InGaN/GaN LEDs, the the superimposed thermal resistanceequivalent circuit network is derived from the characteristics of multi-chips InGaN/GaN LEDs, and a sensorless method to estimate the junction temperature is suggested,moreover, a current redistribution control strategy with the minimal junctiontemperature is given. The advantage casts a light on low-cost realization of the optimaldrive for multi-chips InGaN/GaN LEDs.Finally, based on the suggested9-chips module and optimal driving principle, ahigh-power street lighting lamp is illustrated to realize the adaptive current drive formulti-chips InGaN/GaN LEDs, in which the temperature sensor is not required, andmeanwhile, the further energy saving can be reached.