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This thesis mainly presents a LED driver circuit based on single-stage Flyback converter with power factor correction. Power factor correction technique is applied for constant current driver. Accroding to different magnetize inductance current operating mode, two methods are used to improve the drawbacks of Flyback converter which is operated in open loop. Discontinuous conduction mode is controlled by single loop which is called voltage follower control. Continuous conduction mode is controlled by dual loop, that applied to nonlinear carrier control(NLC). Multiplier is usually used to traditional power factor correction, but it is expensive. To reduce the system cost, a multiplier is removed from NLC. The designed circuit is verified by SPICE software and experiments. From simulation and experimental results, it shows the proposed system achieves the goal with high power factor and constant output current.

In the thesis, a LED driver circuit that is applied in low power LED lighting with constant output current and Power Factor Correction (PFC) is presented. For power stage of LED driver, a non-insulated switching Buck power converter without transformer is used, and develop equivalent mathematical model and block diagram of Buck converter while its inductor current operating in Continuous Conduction Mode(CCM). Furthermore, the closed loop PFC control circuit is designed by time-domain and frequency-domain analysis. In addition, because of the classical PFC control configuration needs the expensive multiplier, a LED driver circuit with PFC without multiplier is presented in this thesis in order to reduce the system cost and space of the circuit. Then, we confirm the designed circuit by simulation and experiment. By the results, the proposed system achieves constant output current control and power factor can reach to 0.92.

In the thesis, an LED driver circuit with Power Factor Correction (PFC) and constant output current is presented. For open-loop LED driver, an insulated switching Flyback power converter is designed, and the Flyback converter will be operated in Continuous Conduction Mode(CCM). One develops equivalent mathematical model for the drivers system. The main part of this thesis is about the design and the study of a closed loop PFC control circuit using inductor voltage sensing technology. In addition, one introduces another traditional inductor current sensing control technique is included to compare with the designed control circuit. Then, one confirms the designed circuits by simulation and the experiment. From the results, the power factor can reach to 0.97, and the expected constant output current control has also been achieved.

This thesis is to design an LED driver circuit with constant output current and Power Factor Correction(PFC) control. Switching power converter is applied for power stage of the LED driver circuit, a non-insulated Buck converter without transformer is used, and the inductor current of Buck converter is operating in Continuous Conduction Mode(CCM). According to the operating principle of Buck converter, the equivalent mathematical model and system block diagram is developed to establish the traditional closed loop PFC control circuit. The controller parameters are set up by time-domain and frequency-domain analysis to achieve the goal with constant output current and PFC control. Furthermore, the thesis presents a more effective PFC control method to reduce the cost of multiplier used in traditional PFC control method and overcome the congenital defect of Buck converter. Both two PFC control methods are confirmed and compared by simulation and experiment. The results show that the proposed control method has more effective performance and achieve constant output current for LED with high power factor by 0.966 under full-load condition.

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No description available.

LED is widely used in many applications, such as indoor lighting, backlighting and street lighting, etc. For these application, multiple LED strings structure is adopted for reasons of cost-effectiveness, reliability and safety concerns. Several methods and topologies have been proposed to drive multiple LED strings. However, the output current balance and efficiency are always the two major concerns for LED driver. A simple two-stage multi-channel LED driver is proposed. It is composed of a buck converter as the first stage and a multi-channel constant current (MC3) CLL resonant converter as the second stage. For the CLL resonant converter, the magnetizing inductance of the transformer can be as large as possible. Therefore, the magnetizing current of the transformer has little influence on the output currents. In addition, the currents of two LED strings driven by the same transformer is balanced by a DC blocking capacitor. As a result, the current balance among LED strings is very good, even if the load is severely unbalanced. Meanwhile, the current flowing through the external inductance Lr1, instead of the magnetizing current is used to help the primary-side switches to achieve ZVS. Therefore, large magnetizing inductance is good for current balance and properly designed Lr1 is helpful for ZVS achievement. These properties of MC3 CLL are preferred to drive multi-channel LED strings. In the design procedure of MC3 CLL resonant converter, the parasitic junction capacitor of the secondary-side rectifier is taken into account. It influences the operation during dead time significantly when the voltage step-up transformer is applied. The junction capacitors of the secondary-side rectifiers, and the output capacitors of the primary-side switches will resonate with the inductor Le2 during the dead time. Finally, this resonance impact the ZVS achievement of the primary-side switches. Therefore, the inductors Lr1 and Le2 should be designed according the charge needed to achieve ZVS with considering the resonance. Additionally, the control strategy for this two-stage structure is simple. Only the current of one specific LED string is sensed for feedback control to regulate the bus voltage, and the currents of other LED strings are cross-regulated. Furthermore, the MC3 CLL is unregulated and always working around the resonant frequency point to achieve best efficiency. The compensator is designed based on the derived small signal model of this two-stage LED driver. Due to the special electrical characteristics of LED, the soft start-up process with a delayed dimming signal is adopted and investigated. With the soft start-up, there is no overshoot for the output current. Finally, a prototype of the two-stage LED driver is built. The current balance capability of the LED driver is verified with the experiment. Good current balance is achieved under balanced and severely unbalanced load condition. In addition, the efficiency of the LED driver is also presented. High efficiency is guaranteed within a wide load range. Therefore, this two-stage structure is a very promising candidate for multi-channel LED driving applications. / Master of Science

With superior longevity, approximately 5 times that of compact fluorescents (CFLs), and high efficacy, around 1.5 times that of CFLs, LEDs are now attracting vast attention from both academic and industrial sectors. Unfortunately, current power supply drivers for LEDs have the following drawbacks: (1) for a two-stage configuration, the power factor correction (PFC) circuit can help LEDs achieve good operating performance but contain too many components and are large in size, have low efficiency and relatively high cost; (2) a single-stage configuration can perform well in PFC and efficiency, however reliability issues occur due to the use of the electrolytic capacitor. In this thesis, the theoretical analysis and implementation of two high power factor, soft-switched, electrolytic-capacitor-less LED drivers are presented. The two drivers solve the aforementioned issues while minimizing its size and cost. The detailed theoretical analysis illustrates the advantages of the presented circuits and provides insight into their design and operation. The simulated and experimental implementations verified the performance of both circuits, which achieve a high power factor, indicating that the drivers have good operating performance. Elimination of the electrolytic capacitors improves the LED drivers’ reliability. In addition, with the help of soft-switching capability, high efficiency is achieved. Simulation and experimental results are presented to support all merits of the two circuits. / Thesis (Master, Electrical & Computer Engineering) -- Queen's University, 2013-04-30 13:22:28.471

In the thesis, LED driver circuits which are applied in low power lighting LED with constant output current and Power Factor Correction are presented. The non-isolated Buck converter are used for the LED drivers. According to different operating mode of inductance current, Power Factor Correction are realized with both the method of Voltage Follower Approach Control under Discontinuous Conduction Mode and the method of Nonlinear Carrier Control under Continuous Conduction Mode. NLC doesn¡¦t need the multiplier which is used in traditional power factor correction, therefore NLC can reduce the system cost. The designed circuits are verified by simulation of IsSpice software and practical experiments. From simulation and experimental results, it shows the proposed approaches achieve the goal with high power factor and constant output current.