Chip-on-board Light-emitting Diode Research Articles

Frame-rate adaptive fractionally spaced equalization enabled high-throughput optical camera communication.

Optical camera communication (OCC) has garnered worldwide research attention, due to its immunity to electromagnetic interference (EMI) and efficient utilization of spectrum resources. However, the limited bandwidth of the OCC system and the timing offset of the camera result in low system throughput. To enhance the OCC throughput, we propose and experimentally demonstrate a frame-rate adaptive fractionally spaced equalization algorithm (FA-FSE) for the joint mitigation of severe inter-symbol interference (ISI) and timing offset arising in OCC. Experimental results validate its correct and power-efficient function, leading to a record aggregated throughput of 250.96 kbit/s, when the 8-level pulse amplitude modulation (PAM-8) signals are independently modulated to eight chip-on-board light emitting diode (COB-LED) light strips, while simultaneously received by a smartphone 10 cm away.

Efficient two-stage offline driver for extra-high-current COB LED applications

This work proposes a reliable and efficient two-stage driver solution for extra-high-current (EHC) chip-on-board (COB) light-emitting diode (LED) applications. An ac–dc boost converter operating in continuous conduction mode is employed to provide input power factor correction and regulated dc-link voltage. Considering that EHC COB LEDs often operate at higher current levels than those employed in conventional high-powered lighting applications, a dc–dc extended gain interleaved buck converter (EGIBC) is employed so that power control is achieved. The average state-space modeling of the EGIBC is derived, while a digital control system is also implemented for this purpose. A 500-W prototype of the proposed two-stage topology is implemented, which does not require electrolytic capacitors. The obtained results clearly demonstrate that the proposed driver complies with international power quality and flicker standards. Thus, it can be consolidated as a viable choice for practical applications involving outdoor floodlighting where high luminous flux is mandatory.

Package structure of polarized white chip-on-board light-emitting diode with high thermal conductivity

The package structure of high power white chip-on-board (COB) light-emitting diode (LED) is investigated. The temperature-dependent performance of the white COB LED combined with a polymeric wire-grid polarizer film (WGF) is optimized. The optimized packaging structure is with a modified phosphor resin layer encapsulated to blue COB LED and an optically transparent plate deposited on the modified phosphor resin layer. The modified phosphor resin comprises a mixture of yellow phosphor and AlN resin for reducing thermal resistance. Results show that the extinction ratio is 83 and the luminous efficacy is 61.4 lm/W at an input power of 8 W for the polarized white COB LED. Without the WGF, the luminous efficacy of the package structure of the COB LED is 90 lm/W.

Improved Photoelectrothermal Model with Thermal Parameters Variation Applied to an Extra-High Current COB LED

This work is mainly concerned with the improved photoelectrothermal (IPET) modeling of an extra-high current (EHC)and extra-high luminous flux (up to 60 klm) solid-state light source based on a chip-on-board (COB) light-emitting diode (LED).The studied COB technology presents the particular challenge of extremely small thermal resistances, with extra-high currentlevels through the lamp (up to 12 A). Considering the unique thermal characteristics of such devices, an improved PET modelingand its respective experimental methodology are detailed. Accurate techniques are also proposed to estimate the device junction temperature.The studied method is very suitable to represent EHC COB devices, since it includes the main thermal parameters variation into a novel model,optimizing the flux prediction for this technology. In this context, the static flux and efficacy are analyzed by means of experimental testsand theoretical model, where the improvement of the employed method is highlighted.

Failure analysis and reliability reinforcement on gold wire in high-power COB-LED under current and thermal shock combined loading

We experimentally and theoretically investigated the failure mechanism of gold wire in high-power COB-LED (chip on board-light-emitting diode) under thermal shock and current combined loading. The samples with electric current were tested under thermal shock loading and the failure modes were analyzed. After the silicone resin dissolved, metallographic microscope was used to observe the failure position of gold wires, the fracture was found occur at the neck of the bond between the first solder joint and gold wire. In the simulation, the characteristics for three types of COB-LED gold wires were studied. We detected some unusual phenomenon such as plastic deformation in the part near the chip which experienced decline instead of rise under low temperature loading. It should, however, be on the rise according to regular speculate. Moreover, results indicate that the strain of failure position reaches 2% (the place where the maximum strain occur on device), which is in great accordance with the experimentally-achieved failure point position. The validity of qualitative and quantitative analysis for LED failure evaluation can be enhanced by the testification between numerical and experimental approach. It implies that we can improve the reliability of COB-LED by using the method which proposed in this work.

Experimental of ultra-high-power multichip COB LED

In solid-state COB (chip on board) LED (light-emitting diode), the process technology is enhanced, brightness of light per power is improved, and optical performance is increased. However, the COB LED chip junction temperature, Tj, is still a disadvantage in critically high hot spots and high temperatures. These disadvantages can shorten life and reduce efficiency. Therefore, Tj must also be solved. From a single-crystal silicon chip packaging LED to multichip COB packaging LED, this tool has become the most mainstream item in the market development of high brightness. Therefore, investigating the research approach and techniques needed to solve the high temperature Tj is necessary. In this study, the system can be used an environment-friendly refrigerant as R407C and R134a systems for a thermal cooling temperature and constant flow compression refrigeration cycle system that cool ultra-high-power multichip COB and high-brightness gallium indium nitride LED heat source. To reduce the COB LED chip, Tj, temperature needs to reach the following specifications: < 125 °C to maximum 150 °C and Tcase < 50 °C to maximum 85 °C. This temperature will maintain good luminous efficiency and long life. In addition, this approach aims to solve the maximum power of thermal dissipation Tj.

Optical Role of Die Bonding for Chip-on-Board White Light Emitting Diode Emitters

Abstract The role of die attach adhesive in influencing light output of the white chip-on-board (COB) light emitting diode (LED) emitters is investigated using Monte-Carlo simulations. It is demonstrated for the first time that the use of an optically clear adhesive for replacing conventional adhesive for multiple COB white LED emitters leads to a significant enhancement in light output of up to 22 %. An optimization of packaging materials and process for multiple COB LED emitter to enhance optical efficiency is also studied.

A study on the radiation heat transfer effect of CNT coating for the single-chip COB LED

In this study, the radiation heat transfer effect of carbon nanotube (CNT) coating on a heat sink with a single-chip COB (chip-on-board) light-emitting diode (LED) was investigated by assessing the junction temperature and thermal resistance. The junction temperature was measured using an infrared camera, and was also simulated using a computational fluid dynamics (CFD) software. The emissivity effects of different CNT volume fraction cases in the coating material were compared. The experiment results showed that the LED chip with the smaller CNT volume fraction had a higher junction temperature. In addition, for accurate results, the emissivity of the CNT coating depending on different CNT volume fractions was determined by comparing the CFD temperature result with the result obtained from the experiment.

Quantitative analysis on air-dispensing parameters for manufacturing dome lenses of chip-on-board LED system

A COB(chip-on-board) LED(light emitting diode) system has advantages such as low cost and good heat dissipation. LED chips are bonded on PCB(printed circuit board) directly without packaging process in case of COB LED systems. Dome lenses made of polymeric resin are generally covered on the bonded LED chips by air dispensing for preventing mechanical damage and making white light. However, it is hard to control the shape of dome lenses precisely due to viscosity of the polymeric resin. We analyzed the relationship of the shape of dome lenses and experimental conditions of the air dispensing in this study. We introduced a new parameter, air pressure * dispensing time, whose physical meaning is impulse per unit area, and obtained much clear relationship of dispensing parameters and shape parameters of the dome lens. This relationship was similar to viscoelastic behavior. The aspect ratio (height over diameter) was increased as the new parameter increased, and was converged to a certain value. The maximum aspect ratio could be calculated by Young’s equation of contact angle.

Red (SrCa)AlSiN3:Eu2+ Nitride Phosphor Particle Size of Phosphor Converted Warm White LEDs

Red (SrCa)AlSiN 3 :Eu 2+ nitride phosphor with different particle sizes were characterized based on physical and luminescent properties, then packaged into Chip-On-Board (COB) Warm White Light Emitting Diode (LED) modules to investigate the influence of particle size on packaging parameters and optical output of the COB LED devices. The phosphor particle sizes investigated were 10µm, 12µm and 14µm, and experimental data indicates that the emission spectrum for the red phosphor with bigger particle size is slightly red-shifted compare with the red phosphor with smaller particle size. Besides that, COB LED modules packaged with smaller red phosphor particle required slightly lesser amounts of phosphor to achieve same value of Correlated Color Temperature (CCT) range from 3500K to 3600K, while enhancing the optical output power. The average lumen output and the average efficacy of COB LED devices packaged with 10µm phosphor had an increment of 5.07% and 9.55% respectively while 12µm phosphor had an increment of 5.14% and 9.79% respectively compared to the 14µm phosphor sample.

Thermal Characteristics of the Optimal Design on 20W COB LED Down Light Heat Sink

Abstract As the demand of the LED for lighting that emits light by p-n junction is increasing, studies on heatproof plate technology is being conducted to minimize the temperature of the LED lighting. As for the temperature of the LED devices, their light emitting efficiency decreases and the maximum lifespan drops down to 1/5. Therefore there are heat dissipation studies going on to minimize the heat. For LED heat dissipation, aluminum heat sink plates are mostly used. For this paper, we designed heat sink that fits residential 20W COB LED Down Light; packaged the heat sink and 20W COB and analyzed and evaluated the thermal properties through a Solidworks flow simulation. We are planning to design the optimal heat sink plate to solve the thermal agglomeration considering TIM(Thermal Interface material). Key words : Heat sink, Solidworks Simulation, LED, Junction Temperature, Optimum Design 1. I NTRODUCTION Due to the increased efficiency and decreased price of the current Light emitting diode (LED) semiconductor, the use of lighting fixtures is growing. The LED lighting fixtures developed for study has been commercialized solving the heat dissipation problem, but as the social demand for high capacity increases, the single heat capacity of semiconductor element is getting larger and various ways to solve heat problems have been proposed. When converting electrical energy into light energy, heat is generated. Such heat and LED’s heat dissipation are important factors to consider when improving the operation of LED and its reliability [1-2]. In general, high power Chip on Board (COB) LED lighting uses the heat sink made of aluminum with insulation area expansion pins installed in it as a cool system dissipating heat on PCB. [3-4]. In order to develop a cooling system, the target amount of dissipation, the environment and possible temperature must be set; and the prediction of heat transfer coefficient and the design of the cooling system should be made[5-6]. In this paper, we will design a heat sink plate for 20W COB LED down light and look at the thermal properties through a Solidworks Flow simulation.