Research On Key Technologies Of High Performance Solid-State Lighting Driver Circuits And Systems

Lighting consumes around 15% of the world’s electric energy production. Represented by incandescent bulbs, fluorescent lamps and halogen lamps, the last generation of lighting technology suffers from poor efficiency, some of the materials also turn out to have water and soil hazards. Research of new light sources and relative lighting technologies are of great significance to reduce greenhouse gases and environmental pollutions. As the most promising candidate from the light sources of the next generation, LED has the advantages of high efficacy, eco-friendly and long lifetime. As LED develops towards high voltage and high current applications, the demands for the relative solid-state lighting driver circuits design is growing. The key issue is to achieve high PF, low EMI/THD and low cost while maintaining high efficiency.This dissertation focuses on the most typical LED driver topologies:the PSR fly-back converter and the sectional linear LED driver. Under the guidance of efficient and precise mathematic models, this dissertation performs deep analysis on the efficiency, stability, electro-magnetic compatibility, reliability and functional expansibility of both structures. Motivated by present flaws of relative driving circuits, this dissertation provides specific optimizing methodologies including control strategies, technical approaches and circuitry implementations. The key innovations of this dissertation are as follows.1. A mathematic model of PSR fly-back converter under DCM is established using discrete-time equations. Based on the proposed model, traditional PSM scheme is introduced to fly-back converters. The simulation results of the output voltage iterative map and modulation factor variation are obtained, showing that although traditional PSM scheme is incompatible with the sampling mechanism of the PSR structure, the output voltage shows no chaotic phenomenon and the ripple is low. The simulation provides adequate theoretical foundations to the introduction of PSM scheme to PSR fly-back converters. According to the variation rules of the modulation factor produced by the traditional PSM scheme, this dissertation provides a self-adaptive PSM strategy suitable for PSR fly-back topology. Through the dynamic evaluation of current load status, the strategy automatically adjusts the modulation factor to achieve stable output voltage with minor ripple. Based on the strategy, the controller is realized by means of combinational and sequential logic circuits, thus introducing PSM scheme to PSR fly-back converters at the cost of a small layout size. The circuitry is realized based on a 1 μm 5V/40V/700V BCD technology. The light-load efficiency of this kind of converter can be optimized by the proposed self-adaptive PSM strategy.2. Aiming at reducing the input current spike in conventional sectional linear LED drivers, a multi-lane fast-feedback structure is proposed. The simulation and experimental results are obtained from the macro model and the prototype, respectively, showing that smooth switching of LED string loads can be achieved, which greatly reduces the EMI and THD signatures of the driver system.3. On the basis of the behavioral pattern of the three-lane fast-feedback sectional linear LED driver and the Ⅰ/Ⅴ curve of LED strings, a behavioural mathematical model is proposed. In comparison with the macro model from Spice simulation tools, the proposed model can accurately predict the key performances of the driver while dramatically reduces the amount of computation, which enables the large-scale traversal operation of the LED amount in each LED sub-string. A three-lane fast-feedback sectional linear LED driver CAD software is developed using the behavioural model. The software can help user to obtain the optimized design parameters, and plot key current and voltage waveforms via GUI. The three-lane fast-feedback sectional linear LED driver is realized by a 1 μm 5V/20V/500V SOI process. A light engine is established based on this driver, so the proposed behavioral model along with the CAD software can be verified. The design productivity is thereby enhanced, to help designers obtain optimum design parameters within short time.4. Based upon the proposed multi-lane fast-feedback structure, a slow-feedback lane structure is introduced by both voltage-varying and impedance-varying methods, thus a connection between the average LED current and a dimming voltage is established. The stability issues are discussed. The slow-feedback lane can greatly expand the design flexibility of sectional linear LED drivers.5. Input voltage tolerance compensation, active OTP, and linear/PWM dimming techniques are proposed based on the slow-feedback lane, aiming at solving relative drawbacks of sectional linear LED drivers. Corresponding circuit implementation methods are provided, and the driver is realized by a 1 μm 5V/20V/500V BCD technology. In order to ease the twice-mains-frequency flickering produced by sectional linear LED drivers, a phase shift technology has been proposed. Certain amount of energy is restored when the input voltage is at the top of its envelope, and will be released to LED strings while the input voltage is at the bottom. Several tests have been performed under different circuit parameter conditions, the experimental results show that the phase shift technology can effectively reduce flicker index and percent flicker with relatively high PF and low THD, which provides more application possibilities for sectional linear LED drivers.