Single stage switched capacitor LED driver with high power factor and reduced current ripple

This paper proposes a resonant switched capacitor-based converter to driver high power light emitting diodes (LEDs). Unlike the traditional switched capacitor based one, the proposed converter uses an inductor to avoid the forced charging and discharging operation reducing stress current in circuit. The proposed converter provides inherent power factor correction (PFC) and the switched capacitors are used as isolation capacitors. The basic description of the topologcy is presented and a 49 W, 220 V ac grid laboratory prototypes has been implemented. The experimental results presented demonstrate the technical feasibility of the proposed converter applied as LED driver.

The proposal of this paper is a modular three-phase ac-dc light-emitting diode (LED) driver for high-power luminaires based on LEDs that uses each phase to control an independent LED load removing in the process both the electrolytic capacitor and the second stage to increase both the lifetime and the efficiency. The driving of each LED load is done by means of a dc-dc converter operating as a loss-free resistor responsible for controlling the current across it. Furthermore, each dc-dc converter needs to achieve power factor correction (PFC) to comply with the restrictive IEC 61000-3-2 class C requirements, hence, achieving unity power factor and low total harmonic distortion. Taking advantage of the light properties, the output of the LED driver will be the sum of the light of each of the phases. Therefore, a theoretical study will be carried out to observe the feasibility of removing the electrolytic capacitor while guaranteeing a flicker-free behavior of the LED luminaire, even if the current of each string is pulsating at twice the mains frequency. This particular performance under high output current and voltage ripples requires reevaluating the well-known limits between the conduction modes in PFC converters. In addition, the theoretical analysis also discusses and proposes control methods for the LED driver, which thanks to its modularity can easily scale in power to drive high-power luminaires. In order to validate the theoretical analysis, a prototype has been built comprised three PFC boost converters disposing of their electrolytic capacitors. The designed prototype operates in the full range of the European three-phase line voltage, which varies between 380 and 420 V, and supplies an output light of 42.000 lm at a maximum power of 300 W while achieving an electrical efficiency of 97.5%.

A conventional offline single-stage light-emitting diode (LED) driver with a high power factor usually produces a significant twice-line-frequency ripple LED current, where the ripple LED current is presented as flickering to human eye. This paper introduces a ripple cancellation method to remove the twice-line-frequency voltage ripple for an offline single-stage LED driver with a power factor correction. Consequently, a dc LED current can be produced to achieve flicker-free LED driving performance. At the same time, the required storage capacitor for the proposed LED driver can be greatly reduced, and the circuit implementation to achieve ripple cancellation is simple. Thus, the overall cost of the proposed LED driver is low. The proposed LED driver also features high efficiency because of its power structure. A 35-W Flyback experimental prototype and a 10-W Buck–Boost experimental prototype have been built to validate the proposed design and demonstrate its optimal performance.

In this paper, a light-emitting diode (LED) driver with a high power factor (PF) and low-frequency current ripple suppression over a wide input range is presented, and a flyback converter is designed to operate in the discontinuous conduction mode (DCM), with a digital controller used to keep the duty cycle constant for half of the utility cycle under a fixed load and input voltage. This method ensures that the input current is in phase with the universal input voltage, thus achieving a high power factor without utilizing feedforward control. Furthermore, on the secondary side, the time of the zero point of the utility voltage can be attained so that the duty cycle can be updated at this time. In addition, a simple auxiliary circuit is connected parallel to the output side to absorb the excess output current of the flyback converter or to release the current to the load to make up for the shortage of the output current of the flyback converter so that the low-frequency ripple of the output current can be inhibited. There are only two current-detecting resistors used in this study: one is the output current-sensing resistor of the flyback converter, and the other is the output current-sensing resistor of the auxiliary circuit.

This paper proposes a single-stage high-efficacy fly back power-factor-correction (PFC) converter with optimization efficiency control for driving multi-string light-emitting diodes (LEDs). The LED driver consists of a fly back converter with PFC mechanism and a constant-current drive circuit with functionalities of efficiency optimization and dimming control. The proposed single-stage LED driver topology features benefits of high power factor and low total harmonic distortion (THD) in low-cost outlay. The pulse width modulation (PWM) dimming mechanism cooperating with the constant-current control circuit completes the LED dimming control. In order to reduce the power dissipations of the dimming circuits, a dynamic voltage regulation (DVR) control is presented to regulate the LED supply voltage by means of the sensing of the drain voltage of the MOSFET in the current controller. While maintaining the desired LED brightness, the DVR technique can minimize the voltage drop of the dimming circuit to enhance the LED driver efficiency further. A 30W white LED driver is devised and a corresponding driver prototype is realized. Testing results are shown experimentally to verify the effectiveness and performance improved of the proposed scheme.

This paper presents the optimal combination design of the light-emitting diode (LED) array for the single-loop continuous-conduction-mode (CCM) buck-boost LED driver. Based on the Taylor series to describe the LED exponential function, the dc and small-signal transfer functions of LED arrays are derived for the system analysis of the employed single-loop CCM buck-boost LED driver. In this paper, the derived system transfer functions of the employed LED driver are verified with SIMPLIS <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> simulation results. The combination design of a 120-piece LED array for the employed LED driver to have power conversion with optimal efficiency is obtained and validated through the theoretical, simulation, and experimental results.

This article proposes a circuit analysis and design for an integrated-stage light-emitting diode (LED) driver that uses a Class-E current-driven rectifier and is connected to a Class-D <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter. The power switches and a dc-bus capacitor are shared. The proposed LED driver can be divided into a two-stage: the power factor correction (PFC) stage uses the output characteristics of a zero-voltage and zero-derivative-switching (ZVDS) Class-E current-driven rectifier as a power-factor corrector; in addition, this PFC stage is designed for the continuous conduction mode (CCM) operation, and the driver stage uses a zero-voltage switching Class-D <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter to supply a constant dc-driven current to the LED load. The circuit operation and step-by-step design of the converter are fully described. The proposed scheme works better with the CCM-ZVDS Class-E current-driven rectifier because it reduces the high current stress on the power switch caused by high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">di/dt</i>. It also gets rid of the need for a differential mode input filter, and a simple non-isolated matching network without a high-frequency transformer can be used. Finally, a 150-W LED street lighting laboratory prototype is implemented, and experimental results are presented to verify the theoretical analyses of the proposed the integrated-stage LED driver.

&lt;span lang="EN-US"&gt;This paper focuses on a single-switch buck-boost (SSBB) converter for light emitting diode (LED) lighting applications. The proposed LED driver with power factor correction (PFC) shows enhanced performance in terms of input power factor, efficiency and reduced voltage stress across the switch. The presented LED driver is operated in discontinuous conduction mode (DCM). The input PFC is carried out using average current mode control (ACMC) and the controller is optimized using artificial bee colony (ABC) algorithm. A hardware prototype of 50W LED driver with ACMC for PFC is implemented using a programmable interface circuit (PIC) microcontroller. The experimental results are presented and the performance is compared with a conventional buck boost LED driver. The proposed SSBB LED driver achieves an input power factor of 0.96 with an efficiency of 98%.&lt;/span&gt;

This paper presents the optimal design of the light-emitting diode (LED) array combinations for three typical nonisolated continuous-conduction mode single-loop control LED drivers. Based on the LED Taylor series model and the equivalent circuits of these three LED drivers, the quality factor functions in their transfer functions of the control-to-output current are derived to predict the optimal combination of the LED arrays according to the given circuit and LED parameters to fulfill the requirement of critical damping and maximum efficiency power conversion, which happen at unity quality factor. The three prototype circuits of three LED drivers with 120 LEDs are presented to verify the optimal design of the corresponding LED array combinations through the theoretical, simulation, and experimental results.

In many applications, such as large-scale LCD panel backlighting, street lighting, tunnel lighting, etc., an ac/dc light-emitting diode (LED) driver should realize the following three functions at least: power factor correction, multichannel constant current outputs, and galvanic isolation. A novel two-stage multichannel constant current ac/dc LED driver with a low cost and simple structure is proposed in this paper, which is composed of a high-frequency resonant ac/ac converter and as many passive LCL-T resonant rectifiers as the number of the output channels. The high frequency resonant ac/ac converter is focused on in this paper, which converts the ac-line input voltage into high frequency sinusoidal output voltage. First, topology derivation of the single-stage high-frequency resonant ac/ac converter is presented, also the operating principle of it. Then, the steady-state performance of it is completely analyzed, including its input power factor, voltage gain, total harmonic distortion of its output voltage, and its soft-switching condition. Finally, a 130 W prototype is built and the experimental results are given to verify the theoretical analysis.

This paper presents a new single phase front-end ac-dc bridgeless power factor correction (PFC) rectifier topology. The proposed converter achieves a high efficiency over a wide range of input and output voltages, a high power factor, low line current harmonics and both step up and step down voltage conversions. This topology is based on a non-inverting buck-boost (Zeta) converter. In this approach, the input diode bridge is removed and a maximum of one diode conducts in a complete switching period. This reduces the conduction losses and the thermal stresses on the switches when compare to existing PFC topologies. Inherent power factor correction is achieved by operating the converter in the discontinuous conduction mode (DCM) which leads to a simplified control circuit. The characteristics of the proposed design, principles of operation, steady state operation analysis, and control structure are described in this paper. An experimental prototype has been built to demonstrate the feasibility of the new converter. Simulation and experimental results are provided to verify the improved power quality at the AC mains and the lower conduction losses of the converter.

In order to provide a constant current to the Light-emitting diodes (LEDs) and to minimize the size and cost of the driver circuit in ac/dc offline LED drivers, electrolytic capacitors are conventionally used due to their high energy density and low cost. However, electrolytic capacitors are sensitive to operating temperature and have much shorter lifetime than the LED semiconductor devices. This paper proposes an improved control scheme that is capable to control the output LED current and regulate the dc-link capacitor's energy simultaneously for a family of single-stage soft-switched high power factor LED driver topologies. Each of these topologies consists of an integrated power factor correction (PFC) circuit. Due to the proposed controller's capability to control the LED current directly via variable frequency control and the dc-link capacitor's voltage via duty ratio control, the required energy storage capacitance can be significantly reduced, thereby allowing small size film capacitor to be used as the energy storage capacitor. Simulation results are provided on two different LED driver topologies, one with an integrated boost PFC stage and the other one with an integrated buck–boost PFC stage, to verify the performance of the proposed control scheme. Experimental results are also been provided on a 12-W prototype to highlight the merits of this paper.

In this paper, one AC light-emitting diode (LED) driver with high power factor (PF) and low total harmonic distortion (THD) is adopted, which is added with the proposed switched LED module and is controlled based on the field-programmable gate array (FPGA). By doing so, the efficiency of such an AC LED driver can be improved significantly. This switched LED module is constructed by several LED strings, which have individual series-connected MOSFET switches. As the switch of the switched LED module is turned on, the corresponding LED string is short-circuited and hence is not conducted, whereas as the switch of the switched LED module is turned off, the corresponding LED string is conducted due to the redundant input voltage across this LED string. Therefore, the redundant input voltage across between the collector and emitter of the BJT current source can be reduced, that is, the unwanted power dissipation in the BJT current source can be decreased, so as to upgrade the efficiency of the overall system.

A novel sectional linear driving method for light‐emitting diode (LED) driver is studied. Considering several issues to be concerned in LED lighting applications, a complete introduction and analysis of the technique is proposed in this study. As the performance of the sectional linear LED driver can be affected by the LED distribution in each LED sub‐string, a behavioural model is established to guide the design. Simulation results are obtained by utilising the behavioural model to optimise the output power and efficiency. The LED driver is fabricated with a 1 µm 5 V/20 V/500 V BCD technology, and a 15‐W T‐8 LED tube light prototype is established on the basis of the driver IC. A series of experiments are conducted to verify the theoretical analysis and the accuracy of the proposed model. The experimental data agrees with the simulation results, above 0.9 power factor (PF) and 90% efficiency are achieved with few peripheral components based on the design guidance made by the proposed model. Both the driving technique and the behavioural model are believed to be useful in the high efficiency, high PF, and cost‐effective ac LED lighting applications.

The amount of light flicker in an AC–DC light-emitting diode (LED) driver is dependent on the size of filter capacitors. In this study, a study is conducted on reducing the size of filter capacitor in an AC–DC buck–boost/flyback LED driver using flicker index and per cent flicker light measures. Using this approach, a procedure for minimising the filter capacitance is presented. It is then concluded that relatively small filter capacitors such as film or ceramic capacitors can be chosen while meeting light flicker requirements. Hence, an LED drive with a longer lifetime can be achieved when compared with a driver using electrolytic capacitors. Experimental studies are presented for a 20 W AC–DC buck–boost/flyback LED driver prototype which utilises ceramic capacitors for driving Cree CR22-32L and XLamp XP-G LED strings.