Proposed LED Driver Research Articles

A Wide-Input-Range Low-Profile Adaptive Delay Compensated Hysteretic LED Driver With Enhanced Current Accuracy

This article presents a wide-input-range low-profile dc–dc-based LED driver. An adaptive delay compensated hysteretic control (ADCHC) is proposed to adaptively modulate both peak and valley inductor currents for minimizing their current deviations, thereby enhancing the accuracy of the average LED current under different input and output voltages. A high-voltage current sensor with passive ripple filtering scheme is also developed to ensure fast and accurate inductor current sensing in the megahertz (MHz) range. The proposed LED driver was realized using two 100-V e-mode GaN FETs as power switches together with on-chip gate drivers and controller implemented in a 0.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , 120-V process. This driver supports an input voltage range from 5 to 100 V and delivers a maximum output power of 25 W. The LED current error is minimized to within ±3.2% of the nominal 350-mA LED current under different input voltages and numbers of output LEDs. Compared with the prior art, the proposed LED driver has the smallest LED current error, operates 2 times higher frequency, and uses <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.5\times $ </tex-math></inline-formula> smaller inductance and inductor volume. The proposed LED driver also features competitive peak power efficiency of 91.7% at 1.8-MHz frequency and 90-V input.

Time-Multiplexed PWM LED Driver With Grayscale Enhancement Techniques for Signage Display

In this article, a pulsewidth modulation (PWM) LED driver is proposed to overcome the challenges of time-multiplexed driving and to enhance the quality of displays sufficient for signage applications. First, adaptive duty cycle restoration (ADCR) compensates for the brightness degradation in low grayscale, where a simple analog timer circuit measures the limited charging time and compensates its effect to ensure the desired emission time. Second, amplitude-segmented PWM (ASPWM) improves the grayscale resolution without increasing the grayscale clock frequency; thus, the electromagnetic interference performance is not sacrificed. The proposed LED driver is fabricated in a 0.18-μm Bipolar-CMOS-DMOS (BCD) process. The measurement results show that the driver Integrated Circuit (IC) achieves a duty cycle restoration factor (DCRF) greater than 0.95 out of ten samples, whereas the DCRF is limited to 0.67 on average when the ADCR scheme is disabled. Resolution enhancement with the proposed ASPWM is verified, achieving 16-b grayscale resolution. The prototype driver IC occupies 3.56 × 3.00 mm of chip area, operated from a 4.5 V supply voltage.

A high-power PCCM LED driver based on GaN eHEMT with hybrid dimming modes

PurposeThe purpose of this study is to design a more flexible and larger range of the dimming circuit that achieves the independence of multiple LED strings drive and can time-multiplex the power circuit.Design/methodology/approachThe state-space method is used to model the BUCK circuit working in Pseudo continuous conduction mode, analyze the frequency characteristics of the system transfer function and design the compensation network. Build a simulation platform on the Orcad PSPICE platform and verify the function of the designed circuit through the simulation results. Use Altium Designer 16 to draw the printed circuit board, complete the welding of various components and use the oscilloscope, direct current (DC) power supply and a signal generator to verify the circuit function.FindingsA prototype of the proposed LED driver is fabricated and tested. The measurement results show that the switching frequency can be increased to 1 MHz, Power inductance is 2.2 µH, which is smaller than current research. The dimming ratio can be set from 10% to 100%. The proposed LED driver can output more than 48 W and achieve a peak conversion efficiency of 91%.Originality/valueThe proposed LED driver adopts pulse width modulation (PWM) dimming at a lower dimming ratio and adopts DC dimming at a larger dimming ratio to realize switching PWM dimming to analog dimming. The control strategy can be more precise and have a wide range of dimming.

Flicker-Free Resonant LED Driver With High Power Factor and Passive Current Balancing

A flicker-free resonant LED driver with high power factor (PF) and passive current balancing is proposed and analysed in this paper. The proposed LED driver are composed a buck power factor correction (PFC) unit and a resonant dc-dc unit by sharing an active switch. Based on this topology, the low output current ripple can be achieved via small voltage ripple on bulk capacitor and fast voltage-mode control loop. By the charge balance for resonant capacitor, the output current of each LED string can be balanced. In a half line cycle, owing to the small voltage ripple on bulk capacitor of pre-stage output, the duty cycle of active switch is almost constant. Therefore, when the inductor current of buck PFC unit operates in discontinuous conduction mode, high PF can be realized. Moreover, as the resonance is existed between resonant capacitor and leakage inductor of transformer, the diodes in resonant dc-dc unit can achieve zero-current turn-off. Thus, the efficiency can be improved. Finally, an 82W LED driver prototype with three-output is built to verify the studied results.

LLC LED Driver with Current-Sharing Capacitor Having Low Voltage Stress

In this paper, an LLC light-emitting diode (LLC LED) driver based on the current-sharing capacitor is presented. In the proposed LED driver, the LLC resonant converter is used to step down the high input voltage, to provide galvanic isolation, to offer a constant current for LEDs. Moreover, the current-sharing capacitor connected to the central-tapped point of the secondary-side winding is used to balance the currents in two LED strings. By doing so, the voltage stress on this capacitor is quite low. Above all, the equivalent forward voltages of the two LED strings are generally influenced by the temperature and the LED current, and this does not affect the current-sharing performance, as will be demonstrated by experiment on the difference in number of LEDs between the two LED strings. In addition, only the current in one LED string is sensed and controlled by negative feedback control, while the current in the other LED string is determined by the current-sharing capacitor. Moreover, this makes the current control so easy. Afterwards, the basic operating principles and analyses are given, particularly for how to derive the effective resistive load from the LED string. Eventually, some experimental results are provided to validate the effectiveness of the proposed LED driver.

Implementation of a Dimmable LED Driver with Extendable Parallel Structure and Capacitive Current Sharing

A dimmable LED driver along with an extendable series structure and interleaved capacitive current sharing is presented herein, the LED connection of which is changed from the traditional series structure to the proposed parallel structure. The number of LED strings can be extended. As the number of LED strings is increased, the output voltage of this LED driver and the voltage stress on the main switch are ideally not influenced. Moreover, only one current sensor is needed to achieve current control and dimming. In this paper, the basic operating principle of the proposed LED driver is described and analyzed. Finally, the effectiveness of this LED driver is demonstrated by experiment based on the field-programmable gate array (FPGA).

Design and analysis of an integrated LC3–Valley fill passive LED driver

ABSTRACTHigh Brightness Light Emitting Diodes (HBLEDs) replace conventional lamps due to energy savings. LC3 parallel resonance principle is used to reduce the total harmonic distortion (THD) for passive LED drivers. The Valley fill concept is applied to reduce the output voltage ripple of LED driver. This paper presents the design and analysis of an integrated LC3–Valley fill passive LED driver suitable for HBLEDs. Valley fill approach is added with LC3 characteristics to further enhance the performance of the LC3-based LED driver. The proposed LED driver achieves high input power factor, low THD with reduced ripple in the output voltage. The integrated passive LED driver consists of inductors, capacitors and diodes only without using any semiconductor-based switching devices and control circuitry. A 70 W driver circuit using single-phase, 230 V, 50 Hz, ac supply is implemented to verify the theoretical analysis. Performance comparison of the integrated LC3–Valley fill passive LED driver is carried out with the existing passive LED driver topologies. An energy efficiency exceeding 95% is obtained.

GaN-Based High-Power-Density Electrolytic-Free Universal Input LED Driver

This paper presents a high-power-density high-power-factor GaN-based two-stage electrolytic-free offline LED driver. The LED driver achieves high power density through the use of a hybrid film-ceramic stacked switched capacitor (SSC) energy buffer, and a comprehensive optimization methodology that evaluates various converter topologies and designs and minimizes overall system volume while maintaining high efficiency. Based on this optimization approach, a totem-pole bridgeless boost power factor correction (PFC) converter is selected for the first stage, while a stacked-input isolated LLC dc-dc converter is selected for the second stage. The optimization procedure also minimizes the passive volume of the SSC energy buffer incorporating the volumetric energy density of commercially available capacitors. The optimized SSC energy buffer utilized in the proposed LED driver has 50% less passive volume than a capacitor-only solution. A 600-W prototype LED driver designed using the proposed approach for universal input voltage (90 - 305 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> ) and 24-V output voltage is built and tested. The PFC stage achieves a peak efficiency of 98% while the LLC stage achieves a peak efficiency of 95%. The prototyped LED driver achieves a power density of 28 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Nonisolated Two-Phase Interleaved LED Driver With Capacitive Current Sharing

In this paper, a nonisolated two-phase interleaved LED driver with capacitive current sharing is presented. In the proposed LED driver, the current sharing capacitor can be used to balance the input inductor currents and the LED currents. Furthermore, only one grounded LED string current is sensed and controlled. Moreover, under the interleaved control, the input current ripple can be reduced. Finally, the operating principles, analyses, and experimental results are provided to verify the effectiveness of the proposed LED driver.

LED driver design for indoor lighting and low-rate data transmission purpose

The LED driver design for lighting at the indoor environment, as well as data transmitter with a one-way link (for download purpose), is discussed clearly in this paper. The LED driver performances are already tested with three scenarios approach and it can work properly. Those approaches are 1) single carrier signal generated by signal generator with offset null as an input signal, 2) integrated with the digital block, i.e. Digital-to-Analog converter (DAC) board which has DC component as an input signal, and 3) using the audio signal as input. The contribution in this paper i.e. 1) the LED driver was simply designed and it could be used for signal with multilevel amplitude format, e.g. audio signals, video signals, orthogonal frequency division multiplexing (OFDM) signal format, etc.; 2) low-cost platform which is built from inexpensive general DIP OP-AMP, 3) can dial up 50 kHz of bandwidth; 4) no flicker effect, therefore harmless for human eyes; 5) light weight implementation and 6) simple to operate with manual tuning. Our proposed LED driver is divided into three stages where each of them, have the main functions, i.e. a) DC-offset remover circuit to remove signal input with has DC signal characteristic, DC-offset summer circuit with a variable amplifier as signal conditioning, and voltage follower transistor.

A Single-Stage PFM-APWM Hybrid Modulated Soft-Switched Converter With Low Bus Voltage for High-Power LED Lighting Applications

In order to design a high-efficiency cost-effective high-power LED driver, a single-stage integrated boost- LLC -type soft-switched ac–dc converter is usually employed. The minimized number of semiconductors and the reduced power loss are its main advantages. However, the high bus voltage is its well-known disadvantage, which is caused by the employment of a conventional pulse frequency modulation (PFM) control strategy with the duty cycle of 0.5. The range of the input ac voltage is severely limited. In order to overcome this problem, a hybrid PFM-asymmetric pulse width modulation strategy is proposed in this paper. The proposed strategy can significantly reduce the bus voltage while maintaining the soft-switching operation for both primary MOSFETs and secondary diodes. Furthermore, the electrolytic capacitors are removed by increasing the bus voltage ripple. Hence, high efficiency, long lifetime, low cost, and universal operation are achieved on the proposed LED driver, which is well matched to the virtues of LED lighting source. The detailed operation principles and design consideration for the proposed modulation approach are analyzed and discussed. The feature of the proposed solution was demonstrated using a universal-input 100-W hardware prototype. The experimental results verified the full-range zero-voltage-switching (ZVS) operation for primary switches and the efficiency achieved 91.6% under the 130-V input voltage.

Single-Stage Single-Switch AC-DC LED Driver with High Power Factor

A single-stage single-switch AC-DC LED driver with high power factor is proposed to overcome the drawbacks of the conventional boost-flyback PFC LED driver. In the proposed LED driver, the boost PFC converter with discontinuous conduction mode (DCM) is adopted to achieve high power factor and the modified flyback DC-DC converter with dual input is integrated to provide electrical isolation and the regulated output voltage. In order to divide input of DC-DC module (dc-link capacitor), the transformer with dual-primary winding is used. Moreover, the leakage inductor currents are absorbed by the dc-link capacitors through a snubber diode and the maximum voltage stress is limited to double DC-link voltage. Therefore, there are virtually no conduction losses by snubber circuit. In additional, some input power is directly transferred to the load and the remaining power is stored in dc-link capacitor. Hence, the total power efficiency is improved. The presented theoretical analysis is verified by prototype of 50kHz and 80W converter.

A Wide-Input-Range Efficiency-Enhanced Synchronous Integrated LED Driver With Adaptive Resonant Timing Control

A wide-input-range DC–DC-based dimmable LED driver is presented in this paper. The proposed LED driver can be automatically configured to operate in the soft-switching mode under the high-voltage condition in order to minimize the converter’s dominant switching power loss. Adaptive resonant timing control is developed to enable proper dead-time generation for on-chip high-voltage power FETs in both hard- and soft-switching modes under different input and output voltages for the power loss minimization. In the proposed LED driver, two low-power body-diode-based zero-voltage detectors and an adaptive resonant timing emulator are also proposed for providing accurate and high-speed zero-voltage switching (ZVS) detection of both power FETs, and achieving optimal quasi-ZVS condition, respectively. Implemented in a 0.5 $\mu \text {m}$ HV CMOS process, the proposed buck-based LED driver can support an input voltage range from 5 V to 115 V and up to 25 series-connected high-brightness LEDs with the maximum output power of 25 W. The LED driver can operate up to 1.6 MHz in the soft-switching mode and 2.2 MHz in the hard-switching mode for providing the peak power efficiencies of 94.4% and 93.6%, respectively. Compared with the state-of-the-art counterparts, this work is the only integrated DC–DC-based dimmable LED driver to demonstrate auto-configurable hard- and soft-switching capability achieving high power efficiency and current accuracy over the widest input voltage range and the largest number of series-connected output LEDs.

Fuzzy Logic Controller Based Bridgeless Isolated Interleaved Zeta Converter for LED Lamp Driver Application

In recent times, High-Brightness Light Emitting Diodes (HB-LEDs) are developing rapidly and it is confirmed to be the future development in lighting not only because of their high efficiency and high reliability, however also because of their other exceptional features: chromatic variety, shock and vibration resistance, etc. In this paper, a Bridgeless (BL) Isolated Interleaved Zeta Converter is proposed for the purpose of reducing the diode failures or losses, the value of output ripples also gets decreased. The proposed BL isolated interleaved zeta converter operating in Discontinuous Conduction Mode (DCM) is used for controlling the brightness of LED Driver with inherent PFC at ac mains using single voltage sensor. The fuzzy logic controller (FLC) is used to adjust the Modulation Index of the voltage controller in order to improve the dynamic response of LED Lamp driver. Based on the error of converter output voltage, FLC is designed to select the optimum Modulation Index of the voltage controller. The proposed LED driver is simulated to achieve a unity power factor at ac mains for a wide range of voltage control and supply voltage fluctuations.

Low-Cost Drive Circuit for AC-Direct LED Lamps

This paper proposes a drive circuit for ac-direct LED lamps. The proposed circuit consists only of a line filter, an LED bridge, a load inductor, a bidirectional switch, and a switch-control circuit. The switch connects the LED bridge to the power line directly. Each leg of the LED bridge consists of LEDs and a protection diode, all connected in series. The load inductor limits the bridge current. The switch operates at a zero current switching condition, so the circuit has high power efficiency. The circuit can operate at a free-volt input condition ( $85 ). For all input voltage conditions the circuit had PE > 89%, luminous efficiency ∼90 lm/W, power factor >0.9, and 120-Hz flicker index ∼0.3. The circuit satisfies the IEC 61000-3-2 Class C and the EN 55015 regulations. The proposed LED driver is well suited for use in household LED lamps.

A Low Power Single-stage LED Driver Operating between Discontinuous Conduction Mode and Critical Conduction Mode

A novel single-stage single-switch (S4) LED driver is proposed in this paper. The paper focuses on the operation principles of the power stage circuit with an operation switched between Critical Conduction Mode (CRM) and Discontinuous Conduction Mode (DCM), including steady state analysis, simulation and backed up by experimental results. The results verify that this proposed LED driver can obtain a high power factor (PF) and the dc output is relatively stable.

LED Driver with TRIAC Dimming Control by Variable Switched Capacitance for Power Regulation

A TRIAC dimming LED driver that can control the brightness of LED arrays for a wide range of source voltage variations is proposed in this paper. Unlike conventional PWM LED drivers, the proposed LED driver adopts a TRIAC switch, which inherently guarantees zero current switching and has been proven to be quite reliable over its long lifetime. Unlike previous TRIAC type LED drivers, the proposed LED driver is composed of an LC input filter and a variable switched capacitance, which is modulated by the TRIAC turn-on timing. Thus, the LED power regulation and dimming control, which are done by a volume resistor in the same way as the conventional TRIAC dimmers, can be simultaneously performed by the TRIAC control circuit. Because the proposed LED driver has high efficiency and a long lifetime with a high power factor (PF) and low total harmonic distortion (THD) characteristics, it is quite adequate for industrial lighting applications such as streets, factories, parking garages, and emergency stairs. A simple step-down capacitive power supply circuit composed of passive components only is also proposed, which is quite useful for providing DC power from an AC source without a bulky and heavy transformer. A prototype 60 W LED driver was implemented by the proposed design procedure and verified by simulation and experimental results, where the efficiency, PF, and THD are 92%, 0.94, and 6.3%, respectively. The LED power variation is well mitigated to below <TEX>${\pm}2%$</TEX> for 190 V < <TEX>$V_s$</TEX> < 250 V by using the proposed simple control circuit.

Analysis and Design Considerations of LLCC Resonant Multioutput DC/DC LED Driver With Charge Balancing and Exchanging of Secondary Series Resonant Capacitors

A new rectifier for multioutput LED driver is proposed based on a charge exchanging and balancing principle in the secondary resonant capacitors. Combined with common ground rectifier and LLCC resonant topology, a four-output dc-dc LED driver is proposed with minimum quantity of secondary charge balancing capacitors. In the LLCC topology, the secondary side resonant capacitors can be used as dc blocking and charge balancing capacitors. The proposed LED driver can automatically share the average output currents by the charge balancing and exchanging among secondary resonant capacitors. The operating principle and the brief design guidelines for the four-output LLCC resonant dc-dc converter are presented. The guaranteed current sharing capability of the proposed four-output LED driver is also analyzed thoroughly. Finally, a 150 W four outputs LLCC resonant dc-dc LED driver is built-up to verify the theoretical analysis.

A 40 V 10 W 93%-Efficiency Current-Accuracy-Enhanced Dimmable LED Driver With Adaptive Timing Difference Compensation for Solid-State Lighting Applications

This paper presents a floating-buck dimmable LED driver for solid-state lighting applications. In the proposed driver, an adaptive timing difference compensation (ATDC) is developed to adaptively adjust the off-time of the low-side power switch to enable the driver to achieve high accuracy of the average LED current over a wide range of input voltages and number of output LED loads, fast settling time, and high operation frequency. The power efficiency benefits from the capabilities of using synchronous rectifier and having no sensing resistor in the power stage. The synchronous rectification under high input supply voltage is enabled by a proposed high-speed and low-power gate driver with pseudo-digital level shifters. Implemented in a 0.35 μm 50 V CMOS process, experimental results show that the proposed LED driver can operate at 1 MHz and achieve peak power efficiency of 93% to support a wide range of series-connected output LEDs from 1 to 10 and a wide input range from 10 to 40 V. The proposed LED driver has only 2.8% current error from the average LED current of 345 mA and settles within 8.5 μs after triggering the dimming condition, improving the settling time by 14 times compared with the state-of-the-art LED drivers.

A Novel Flyback LED Driver Based on Primary Side Feedback without Auxiliary Winding

A novel flyback LED drive based on primary side feedback without auxiliary winding is proposed in this paper. Photoelectric couple or auxiliary winding must be used to detect the current conducted through secondary side in prior LED driver system. But it causes insecurity isolation and both raises the manufacturing cost accordingly. The proposed voltage coupled network can estimate zeros crossing point of secondary current and sets the right time to turn on the switch MOS transistor after a delay time. And the current sense circuit is utilized to sense the current flows through the primary side, turning off switching transistor when the primary current rising up to a setting value. The proposed LED driver is suitable for discontinuous conduction mode (DCM). The experimental results verified theoretical analyses.