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In this paper, the application and design of a high-power factor isolated Ćuk converter-based LED driver are realized for up to 50 W power. For the power switch of the PFC isolated Ćuk converter, traditional Si and silicon carbide (SiC) MOSFETs, which are wide bandgap semiconductors, are used and compared. The application is conducted using a dsPIC30F4011 microcontroller including PI voltage control. A current sensor is added to limit maximum current. Moreover, PI control parameters are selected by genetic algorithm to avoid a complex mathematical procedure for controller design. The power LED model derived in this paper is used for the PI parameter selection process. In addition, the input side inductor of the converter is operated in discontinuous conduction mode, and the switching frequency of the power switch is 57 kHz. With the experimental setup, the total harmonic distortion (THD) of grid voltage and current, power LED voltage and current, switch voltage, and input side inductor current are shown for both the SiC and Si MOSFETs and compared. It is concluded from the application that the SiC-based driver gives better results than the Si-based driver on the basis of THD and efficiency. Further, both applications provide limits of IEC61000-3-2 C class standard. [ABSTRACT FROM AUTHOR]

This work presents an analysis and a design methodology for a DC–DC LLC resonant converter applied to off-line LED driving. An investigation regarding the main design parameters that influence the LED low-frequency (LF) ripple has been carried out. The study was based on a mathematical analysis of the converter and employs numerical algorithms to solve a set of equations that accurately describe the converter behavior. Based on this analysis, a novel design methodology that allows for LF current ripple prediction has been devised. A numerical model has been developed to determine the LF current ripple transmission in DC–DC LLC resonant converters and provide a methodology for designing the bus capacitance in two-stage off-line LED power supplies. The work shows that the design of the LLC resonant converter for off-line LED driving is a trade-off between the converter efficiency and the LF ripple transmission. Experimental results were taken from two 46-W laboratory prototypes considering two different design goals: one for LF ripple reduction and another aiming at the highest converter efficiency and better power quality. Furthermore, the design of a two-stage LED driver based on an LLC converter taking into account the LF ripple transmission is also presented. [ABSTRACT FROM AUTHOR]

An MC3 LLC resonant light-emitting diode (LED) driver is a multi-channel constant current (MC3) output solution based on LLC resonance. Through an effective combination of multiple transformers and a DC block capacitor, this driver allows constant current outputs in multiple channels when the LED channels are unbalanced. This study considers a fuzzy self-tuning proportional integral derivative (PID) control strategy that allows for the self-tuning of PID parameters according to fuzzy inference rules designed using the relationship between the current gain and the switching frequency. Thus, when LED channels are unbalanced, the system allows a constant current output for each of the channels and controls the input voltage disturbances well. Simulation and experimental verifications are carried out, and a 20 W 4-channel constant current power supply design based on LLC resonance is obtained for the LED driver. This realizes soft-switching of the switching device, which reduces system loss and improves system efficiency. Moreover, the adjustment time of the proposed method is half that of fixed-parameter control methods, and the overshoot of the proposed method is smaller than that of fixed-parameter control methods. When compared with PID controllers with fixed parameters, the proposed method is more robust. When a system is disturbed, it recovers faster and has a smaller range of current fluctuation with the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, current-mode boundary conduction mode (BCM) of a high-efficiency LED driver with high power factor, utilizing low-voltage film capacitors, is presented, and its theoretical design and considerations are discussed. The 1.5-stage driver consists of a forward-flyback and buck converter. Higher efficiency was reached using the reduced redundant power processing approach. Most of the processed energy is transferred to the output through flyback, while the rest removes the low harmonic ripple in the output current through the forward-buck path. An acceptable amount of odd harmonics is injected into the input current by using current-mode BCM control method, further reducing bus capacitance. To validate these principles, a laboratory prototype has been built and experimental results of a high-current 85 W (29.5 V/2.9 A) lamp with 50 Hz, 185–255 V power supply are provided. The results show that output current ripple is low, and the input current harmonics are within the standard regulations. [ABSTRACT FROM AUTHOR]

Multiple output LED drivers are necessary to achieve better performance and higher reliability in street lighting, tunnel lighting and LCD background lighting applications. Based on LCL-T constant-current characteristics, a modular multiple output LED driver is proposed in this paper. The LCL-T rectifiers are connected to the same voltage bus and work like current sources. However, since there are much higher voltage harmonics in the AC square bus voltage, it is very important to quantitatively analyze how these harmonics influence the precision of the output currents. In addition, all of the switches can achieve Zero Voltage Switching (ZVS) by proper design of the LCL-T network. Finally, a 200-W prototype with five channels is established with an efficiency of 92.25%. [ABSTRACT FROM AUTHOR]

A TRIAC dimmable LED driver with a wide tuning range and a two-stage uniform dimming scheme is proposed in this paper. To solve the restricted dimming range problem caused by the limited conduction ratio of TRIAC dimmers, a conduction ratio compensation technique is introduced, which can increase the output current up to the rated output current when the TRIAC dimmer turns to the maximum conduction ratio. For further optimization, a two-stage uniform dimming diagram with a rapid dimming curve and a slow dimming curve is designed to make the LED driver regulated visually uniform in the whole adjustable range of the TRIAC dimmer. The proposed control chip is fabricated in a TSMC 0.35µm 5V/650V CMOS/LDMOS process, and verified on a 21V/500mA circuit prototype. The test results show that, in the 90V/60Hz~132V/60Hz ac input range, the voltage linear regulation is 2.6%, the power factor is 99.5% and the efficiency is 83%. Moreover, in the dimming mode, the dimming rate is less than 1% when the maximum dimming current is 516mA and the minimum dimming current is only about 5mA. [ABSTRACT FROM AUTHOR]

In order to reduce the cost, improve the efficiency and simplify the complicated control of existing isolated LED drivers, an improved boundary conduction mode (BCM) Buck ac-dc light emitting diode (LED) driver with extended output voltage and low total harmonic distortion is proposed. With a coupled inductor winding and a stacked output, its output voltage can be elevated to a much higher value when compared to that of the conventional Buck ac-dc converter, without sacrificing the input harmonics and power factor. Therefore, the proposed Buck LED driver can meet the IEC61000-3-2 (Class C) limitation and has a low THD. The operating principle of the topology and the design methodology of the ac-dc LED driver are presented. A 150 W ac-dc prototype was built in the laboratory and it shows that the input current harmonics meet the lighting standard. In addition, the THD is less than 16% at a typical ac input. The peak efficiency is higher than 96.5% at a full load and a normal input. [ABSTRACT FROM AUTHOR]

A fixed off-time controlled high power factor ac-dc LED driver is proposed in this paper, which employs a novel zero-crossing-compensation (ZCC) circuit based on a fixed off-time controlled scheme. Due to the parasitic parameters of the system, the practical waveforms have a dead region. By detecting the zero-crossing boundary, the proposed ZCC circuit compensates the control signal VCOMP within the dead region, and is invalid above this region. With further optimization of the parameters KR and Kz of the ZCC circuit, the dead zone can be eliminated and lower THD is achieved. Finally, the chip is implemented in HHNEC 0.5pm 5V/40V HVCMOS process, and a prototype circuit, delivering 7~12W of power to several 3-W LED loads, is tested under AC input voltage ranging from 85V to 265V. The test results indicate that the average total harmonic distortion (THD) of the entire system is approximately 10%, with a minimum of 5.5%, and that the power factor is above 0.955, with a maximum of 0.999. [ABSTRACT FROM AUTHOR]

In applications for indoor illumination, light-emitting diode (LED) is widely used. The requirements for small volume, low cost and high reliability LED driver makes additional challenges. Conventional single stage flyback LED driver requires additional feedback components such as opto-coupler or auxiliary winding. These components take space on printed circuit board, reduce the reliability and may introduce interference into the feedback loop. A 2.7 W LED driver without opto-coupler or auxiliary winding is proposed. With novel demagnetizing time sampling method, the feedback circuit is fully integrated into the controller, leaving few off-chip components. The controller integrated circuit (IC) is fabricated in CSMC 0.8 μm 500 V BCD process to verify the proposed sampling method. A power MOS is also integrated into the controller IC to simplify the off-chip circuit further. A prototype of the driver is also built and optimized to reduce the volume into 1.6 × 2.4 × 1.4 cm. The experimental results show that the efficiency is above 72.75 % and the average output current variation is less than 5 % under universal input voltage. [ABSTRACT FROM AUTHOR]

A high power factor (PF), high efficiency light-emitting diode (LED) driver without off-chip inductor and capacitor is presented in this paper. The proposed driver consists of one resistor, one diode bridge and one controller integrated circuits (IC). The controller IC employs four LED strings and sequences their conduction to shape the output current in proportion to the input voltage. The controller IC was designed and implemented by using HHNEC 1 μm 700 V process. The experimental results show that high PF of 97.93 % and efficiency of 90.41 % under the input voltage of 220 V|rms utility voltage were obtained. [ABSTRACT FROM AUTHOR]

A novel vehicle headlamp low beam system is presented. The optical system is composed of three identical cells to ensure enough illumination. A poly-ellipsoid reflector and a aspherical lens are used to concentrate the rays and a baffle is employed to produce the cut-off line. The optical performance shows a good agreement with the requirement for headlamp in Chinese national standard. The smart constant current driver sustains automotive headlamps᾿requirements, moreover it has high power efficiency. The performance of three kinds of cooling systems with different structures are simulated and evaluated by FloTHERM software. Then a loop heat pipes combined with fins cooling system is manufactured for cooling the designed LED headlamp. It can greatly improve the cooling efficiency. Even in the 80°C environmental temperature, it can meet the working requirements of LED headlamp low beam system, so it is a kind of feasible cooling scheme. [ABSTRACT FROM AUTHOR]

This paper discusses theoretical analysis of the efficiency of a light emitter diode (LED) driver using a charge pump. It is shown that the maximum efficiency of a conventional LED driver using a charge pump is determined only by the ratio of a forward voltage of an LED and a nominal output voltage of a charge pump. Theoretical analysis reveals that the efficiency does not depend on values of flying capacitors and output capacitors, clock frequency, duty cycle and on-resistance of switches. Minimizing the difference of an output voltage of a charge pump and a forward voltage of an LED is important to minimize power loss of an LED driver. In order to reduce power loss caused by charging capacitors, a novel charging procedure named multi-step charging technique is proposed. Some charge pumps using multi-step charging technique are shown and validity of the proposed multi-step charging technique is confirmed. [ABSTRACT FROM AUTHOR]

A digital controller IC for the flyback converter with primary-side feedback is proposed. The controller is used for adapter charger or LED driver applications. To obtain high accuracy for the primary-side feedback, a digital primary-side sensing technology is adopted, which can auto-track the knee point of the primary auxiliary winding voltage. Furthermore, an internal digital compensator eliminates the need for external loop compensation components while achieving excellent line and load regulation. The controller could output both constant voltage and constant current depending on the load current. Pulse width modulation and pulse frequency modulation are used in constant voltage mode while quasi-resonant control is used in constant current mode. The digital controller is validated by using FPGA. [ABSTRACT FROM AUTHOR]

This paper proposes a primary side constant power control scheme for TRIAC dimmer compatible LED drivers. The LED driver is a Flyback converter operated in boundary conduction mode (BCM) to minimize the switching loss. With the proposed control scheme, the input power of the Flyback converter can be controlled by the TRIAC dimming angle, which is not affected by AC input voltage variations. Since the output voltage is almost constant for LED loads, the output current can be changed by controlling the input power with a given conversion efficiency. The isolated feedback circuit is eliminated with the proposed primary side control scheme, which dramatically simplifies the whole circuit. In addition, the input current automatically follows the input voltage due to the BCM operation, and the resistive input characteristic can be achieved which is attractive for TRIAC dimming applications. Experimental results from a 15W prototype verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents a secondary-side, dual-mode feedback LLC resonant controller IC with dynamic PWM dimming for LED backlight units. In order to reduce the cost, master and slave outputs can be generated simultaneously with a single LLC resonant core based on dual-mode feedback topologies. Pulse Frequency Modulation (PFM) and Pulse Width Modulation (PWM) schemes are used for the master stage and slave stage, respectively. In order to guarantee the correct dual feedback operation, Phased-Locked Loop (PLL)-based automatic duty control circuit is proposed in this paper. The chip is fabricated using 0.35 μm Bipolar-CMOS-DMOS (BCD) technology, and the die size is 2.5 mm × 2.5 mm. The frequency of the gate driver (GDAIGDB) in the clock generator ranges from 50 to 425 kHz. The current consumption of the LLC resonant controller IC is 40 mA for a 100 kHz operation frequency using a 15 V supply. The duty ratio of the slave stage can be controlled from 40% to 60% independent of the frequency of the master stage. [ABSTRACT FROM AUTHOR]

This paper proposes a triple mode LED driver integrated with 16bit level sensitive analog front end by 0.25 μm CMOS process for portable application. The LED driver needs to regulate single LED current with 0.9-3.6 V voltage to support several types of battery. The output range is 2.5-4 V which requires voltage step-up and step-down. A step-up/step-down converter can do this with a lot complexity, more components, lower efficiency and requirement of high voltage switches which adds extra manufacture cost. Our proposed topology avoids complicated step-up/step-down topology. It has triple modes: Boost PWM mode, PFM mode, LDO mode to cover different input voltage range. The mode control is implemented by simple circuit and gives smooth mode transition and very stable LED current. The simple topology makes it possible to use two stack 3 V IO devices as internal power switch to tolerate max to 5.7 V. By careful design and layout, LED switching activity only degrades the 16bit level analog front end SNR by 1 dB. [ABSTRACT FROM AUTHOR]

Occurrence or non-occurrence of saddle-node bifurcation in a buck converter with constant current load under current or voltage mode control is analyzed. The bifurcation critical conditions are derived. The required compensating ramp slope to avoid the bifurcation is also derived. The derived condition is useful to design a stable buck converter as a light emitting diode (LED) driver to avoid the bifurcation. The bifurcation occurs only in some control schemes. When the control scheme makes the converter operate like a current source, the bifurcation occurs. When the control scheme makes the converter operate like a voltage source, the bifurcation does not occur. [ABSTRACT FROM AUTHOR]

The proposed high-efficient WLED driver using light-balanced-controlled techniques with current-locked loops is presented in this paper. This LED driver has 500:1 current sensing ratio and 1 kHz PWM dimming frequency. The maximum output current of the buck converter is 100 mA and the output voltage range is from 3.5 to 4.8 V with a 20 and 18 μH off-chip capacitor and inductor, respectively. The maximum efficiency of the proposed LED driver is 87.8 % and the current difference between each LED string is 1.33 %. And it is fabricated with TSMC 0.35 μm 2P4 M CMOS processes. The chip area is 1.52 mm × 1.36 mm. [ABSTRACT FROM AUTHOR]