Single-Stage LED Driver Achieves Electrolytic Capacitor-Less and Flicker-Free Operation With Unidirectional Current Compensator

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%.

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.

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.

Light‐emitting diode (LED) drivers in outdoor street lighting applications suffer from short‐lifetime because of the prolonged exposure to harsh environmental conditions such as high operating temperature, high humidity etc. A long‐lifetime multi‐channel LED driver consisting of front‐end AC–DC boost power factor correction (PFC) converter followed by a DC–DC power conversion stage with dimming capability for LED‐based street light is proposed in this study. This LED driver uses an inductor‐based auxiliary decoupling circuit at the output of the AC–DC converter for mitigating the double‐line‐frequency power ripple present in the DC bus. The inductive ripple power storage circuit has a longer lifetime than a conventional capacitive storage circuit which is usually implemented by electrolytic capacitors. A digital control method is proposed to realise the decoupling control along with PFC control by a single non‐digital signal processor micro‐controller ST STM32F103RBT6. The proposed LED driver for street lighting is analysed and validated on a 150 W test setup. A comparison of active decoupling AC–DC converters for eliminating secondary‐harmonic power ripple is displayed.

This paper presents a mean-peak current control (MPCC) buck dimmable light-emitting diode (LED) driver for automotive headlamp lighting applications. The proposed MPCC scheme can provide precise inductor current regulation during dimming operations by employing an integrator to enhance the accuracy of the LED average current. To address electromagnetic interference (EMI) issues in LED driver operation, adoption of a frequency jitter oscillator reduces the EMI amplitude of critical signals. Under typical operating conditions, the system clock signal exhibits random frequency jittering within $\pm 5 \%$ of the 175 kHz center frequency. The adoption of a soft-start circuit prevents potential chip damage caused by inrush current during startup by gradually ramping up the integrator reference voltage to eliminate surge current. Implemented in a $0.35-\mu \mathrm{m}$ HV CMOS process, the proposed LED driver achieves 1% LED current error and 96.7% peak efficiency over an input voltage range of 6 to 60 V while driving 1 to 20 LEDs.

In the field of non-isolated light-emitting diode (LED) driver, the omnipresent buck-based LED constant current driver shows poor efficiency in occasions of high step-down ratio due to the marginal operating duty cycle. In order to overcome such drawback and to provide an alternative topological scheme for an LED driver, a Watkins-Johnson topology-based solution is proposed in this paper, by improving the original circuit structure into a dual low-side power switch version and introducing a feedback network for regulating the output current to a constant level. Theoretical analysis, including accurate model construction, steady-state analysis, dynamic analysis, and design consideration, is conducted. Also, an experimental prototype is realized to drive all kinds of LED arrays for acquiring electrical parameters and evaluating performance. The innovative points include invoking the low-side-ize approach to realize the power circuit transformation, and furthermore, theWatkins-Johnson topology is first applied to the constant current power supply. The proposed LED driver holds salient features of low-terminal current ripple, ease of driving, high-voltage conversion ratio tolerance, and inherent energy recovery functionality. The application scope covers low-voltage dc input or automotive lighting use.

In this paper, a cost-effective single switch multi-channel LED (light emitting diode) driver is proposed. While conventional LED drivers require as many non-isolated DC/DC converters as the number of LED channels, the proposed LED driver needs only one power switch and several balancing capacitors instead of expensive non-isolated DC/DC converters. Therefore, the proposed driver features a simpler structure, with a lower cost and a higher efficiency. Because its power switch can be turned off under the zero current switching condition, it has very desirable advantages such as improved electromagnetic interference characteristics and high efficiency. Moreover, it uses only a small number of DC blocking capacitors with no additional active devices for the current balancing of multi-channel LEDs. As a result, the proposed driver exhibits high reliability and is cost effective. To confirm the validity of the proposed driver, a theoretical analysis is performed, and design considerations and experimental results obtained from a prototype that is applicable to a 46" LED-TV are presented.

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.

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.

In this study, a new method is proposed to replace electrolytic capacitors with a long life-span capacitor in light-emitting diode (LED) drivers. In this method, odd harmonics of AC network are injected into the input current up to nineteenth order, to eliminate power imbalance between input and output. For a better control, LED driver has considered as a two-stage driver. The injected harmonics and some of the circuit parameters such as output capacitors and control parameters of the first stage and second stage were determined by genetic algorithm. After applying the proposed method and performing the simulation, output capacitors were obtained less than 10 μF, which can be easily replaced with long-life capacitors. In addition, the essential requirements and standards for input current and output current were observed.

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.

A novel dimmable light‐emitting diode (LED) driver is proposed in this study. The circuit topology uses two active switches. One active switch shared by a buck–boost converter and a buck converter is operated at high‐switching frequency while the other one is low‐frequency pulse‐width modulated to dim high‐power LEDs. The buck–boost converter plays the role of a power‐factor corrector. It operates at discontinuous‐conduction mode to waveshape the line current to be sinusoidal and in phase with the input‐line voltage. The buck converter regulates the dc‐link voltage to output a low‐frequency pulse‐width modulation (PWM) voltage to drive high‐brightness LEDs. Since only one power‐conversion process is required, and the buck converter works only when the low‐frequency PWM voltage is at a high level, the proposed LED driver has the advantage of high efficiency. Besides, it achieves unity power factor and low total current harmonic distortion.

Light emitting diode (LED) lamps with ac-input (50 or 60 Hz) usually require an electrolytic capacitor as the dc-link capacitor in the driver circuit to: 1) balance the energy between the input and output power, and 2) to minimize the low-frequency component of the output ripple across the LEDs. The lifetime of this capacitor, however, is much shorter than that of a LED. To maximize the potential lifetime of the LED lighting system, a new pulsating current driving LED driver that does not require any electrolytic capacitors or complicated control circuits to minimize the low-frequency (i.e., 100 or 120 Hz) output ripple is proposed in this paper. The proposed circuit is simple and a single-switch topology is designed to simplify the controller design. The proposed circuit is able to reduce the energy storage capacitance to a few microfarads range, so that film capacitor can be used to replace the unreliable electrolytic capacitor. The circuit operating principles and its theoretical analysis are provided in this paper. Simulation and experimental results are given on a 9-W LED lamp to highlight the merits of the proposed circuit.

With the development of new technologies, LEDs (light-emitting diodes) take a significant position in lighting due to their long-life spans and high luminous efficacy, which result in energy and maintenance cost savings. These efficient and innovative light sources require adequate ballast or electronic control gear, also known as LED drivers, for their operation. An LED driver provides appropriate voltage level and current for the operation of LEDs. It converts and rectifies higher voltages of alternating current to lower voltages of direct current and regulates the current flowing through LEDs at a nominal level. There are many advantages and disadvantages to using LEDs, primarily caused by LED circuits and LED drivers. The dimming influence of outdoor LED lighting on the LED driver performance is analysed in this paper, specifically the testing of an LED lighting driver by changing the load level. Results of LED driver efficiency calculated from measured input and output power, output voltage ripple measurements, and total harmonic distortion analysis are shown. Based on the measurement results, significant recommendations and concluding remarks are given.

The electrolytic capacitor is the mainly component that impact the working lifetime of light-emitting diode (LED). If an ac-dc LED driver with ripple cancellation method, the electrolytic capacitor eliminate is of vital importance. Therefore, this paper present a solution with secondary side full-bridge structure for cancel the twice ac line ripple from the LED driver. In order to reduce the components cost and LED driver volume, a single-stage high efficiency electrolytic capacitor less isolate ac-dc LED driver is implement and discussed in detail, which is a discontinue conduction model (DCM) power factor correction (PFC) buck-boost converter integrated a isolate flyback converter. Finally, a 100W prototype has been built and tested. Experiment results demonstrated the effectiveness and high feasibility of the proposed LED driver.