High‐power‐factor dimmable LED driver with low‐frequency pulse‐width modulation

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 dimmable LED driver with cascaded magnetic amplifiers is proposed for multistring applications. A master power converter is used to provide the major part of the voltage for a plurality of slave converter modules with magnetic amplifier control. The magnetic amplifiers are used to regulate only the varying part of the LED string voltage and therefore greatly reduce the power losses in parallel converter modules. Good current balance among the parallel LED strings and a high energy efficiency in the range of 86-88% has been achieved for a 21W practical prototype formed with 3 parallel strings.

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%.

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.

&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;

AC-connected light emitting diode (LED) drivers experience imbalanced energy between input and output in a half-line cycle. To achieve the flicker-free operation, the imbalanced energy needs to be buffered, often by energy-dense electrolytic capacitors. However, electrolytic capacitors are also well-known for their short lifespan. These capacitors are the limiting factor of an LED drivers’ lifespan. High voltage film capacitors and a buck converter have been used in the proposed LED driver to buffer the imbalanced energy. When P in > P LED, the extra energy is transferred from the ac input directly to the high voltage film capacitors. When P in P LED, the energy is transferred from the high voltage film capacitors to the output by the buck converter. The imbalanced energy goes through two power conversion steps in the proposed LED driver, which is one time less than other comparable electrolytic capacitor-less designs, enabling a higher efficiency to be achieved. A 28 W flyback topology based experimental prototype had been built and tested to verify the proposed design.

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.

This paper proposes a novel light-emitting diode (LED) driver consisting of a buck-boost converter and a buck converter. Each converter adopts a power MOSFET as the active switch. With no need to use any auxiliary switches or snubber circuits, both active switches can operate at zero-voltage switching on (ZVS) by freewheeling the inductor current of the converters to flow through the intrinsic diodes of the MOSFETS. The buck-boost converter is operated at discontinuous-conduction mode (DCM) to perform the function of power-factor correction to ensure almost unity power factor at the input line. The buck converter steps down the output voltage of the buck-boost converter to drive LEDs. It could be designed to operate at either DCM or continuous-conduction mode. The detailed circuit operations and analysis are provided. A prototype 60-W LED driver was built and tested. Experimental results show that the switching losses can be effectively reduced by operating the active switches at ZVS. The measured power factor and circuit efficiency are as high as 0.99% and 93%, respectively.

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.

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.

White light emitting diode (LED) with high brightness has attracted a lot of attention from both industry and academia for its high efficiency, ease to drive, environmental friendliness, and long lifespan. They become possible applications to replace the incandescent bulbs and fluorescent lamps in residential, industrial and commercial lighting. The realization of this new lighting source requires both tight LED voltage regulation and high power factor as well. This paper proposed a single-stage flyback converter for the LED lighting applications and input power factor correction. A type-II compensator has been inserted in the voltage loop providing sufficient bandwidth and stable phase margin. The flyback converter is controlled with voltage mode pulse width modulation (PWM) and run in discontinuous conduction mode (DCM) so that the inductor current follows the rectified input voltage, resulting in high power factor. A prototype topology of closed-loop, single-stage flyback converter for LED driver circuit designed for an 18W LED lighting source is constructed and tested to verify the theoretical predictions. The measured performance of the LED lighting fixture can achieve a high power factor greater than 0.998 and a low total harmonic distortion less than 5.0%. Experimental results show the functionality of the overall system and prove it to be an effective solution for the new lighting applications.

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.