Management Of High-power Light-emitting Diodes Research Articles

Thermal management of high-power LEDs based on integrated heat sink with vapor chamber

An integrated heat sink with vapor chamber (IHSVC) is developed in this study for the thermal management of high-power light-emitting diodes (LEDs). The wick, asa key component of the IHSVC, is featured with parallel and orthogonal microgrooves, which were made using the micromilling method. Systematic experiments are conducted to characterize the thermal and optical performances, and the IHSVC is compared with the conventional heat sink (CHS) under the same operating conditions. Temperature rising tests indicate that the junction temperatures of the IHSVC system are always lower than those of the CHS at any current. In addition, the total thermal resistance Rj-a (from the junction to the ambient) of the IHSVC system is 0.83°C/W, which is 16.5% lower than that of the CHS at 3200mA (approximately 130W). The temperature distribution of the IHSVC is also more uniform. As for the optical performance, the luminous fluxes and luminous efficacy of the IHSVC system are higher than those of the CHS device. Furthermore, it is found that the junction temperature has a negativeeffect on radiant efficiency. The radiant efficiency of the IHSVC system always outperforms its counterpart under the same junction temperature. The experimental results show that the high-power LED yields a favorable performance using the IHSVC unit.

New Applications of an Automated System for High-Power LEDs

An automatic system based on thermoelectric cooler (TEC), a microfan, and microcontroller is first applied to thermal management of high-power light-emitting diodes (LEDs). Its hardware is composed of microcontroller as a control core, K-type thermocouples as acquisition devices, and TEC and a microfan with heatsink as cooling vehicles. The experiment confirms that the LEDs substrate temperature can be controlled effectively, and indicates that the LED chips are operating reliably. Specifically, in high-temperature environments of 43 °C, the system can automatically drop to the low set temperature (30 °C) due to thermoelectric effect driven by TEC. Heat transfer analysis shows that maximum LED power cooled by the system is 106.7 W, and the total power consumption of the automatic cooling system is only 8.85 W. The automatic cooling system has a high cooling efficiency.

Novel Thermoelectric Modules for Cooling Powerful LEDs: Experimental Results

We present the results of an experimental study of a cooling system based on a novel thermoelectric module specifically designed for thermal management of high-power light-emitting diodes (LEDs). The Seoul Semiconductor LED W724C0 device was chosen for experimental validation of the efficiency of the proposed cooling unit. Two cooling systems with identical heat sinks were tested for comparison: a state-of-the-art one based on an insulated metal substrate-printed circuit board (IMS-PCB), and a system with thermoelectric cooling. The obtained results show that use of thermoelectrics results in a considerable reduction of the LED operating temperature, providing increased light output and greatly increased LED lifetime.

Hotspot Location Shift in the High-Power Phosphor-Converted White Light-Emitting Diode Packages

Thermal management of high-power light-emitting diodes (LEDs) plays an important role in determining their optical properties, reliability, and lifetime. In this paper, we present a method to study the temperature field of phosphor-converted LED packages by combining the Monte Carlo optical simulation and finite element simulation together. The temperature field, including the heat generation in both LED chip and phosphor layer, are presented and analyzed. It was found that temperature increased with the increase in phosphor concentration and the hotspot location in remote phosphor-coating packages shifted with the changes in phosphor concentration, while there was no shift in direct phosphor-coating packages. It was concluded that the hotspot location in the high-power phosphor-converted white LED packages depended on phosphor concentrations as well as packaging methods.

Cooling of high power LEDs through ventilating ambient air to front surface of chip

In this study, a novel cooling strategy through ventilating ambient air to the front surface of the hot chips of the high power light-emitting diodes (LEDs) was proposed to tackle the ever tough issues facing the conventional thermal management approaches. Preliminary thermal resistance analysis, numerical simulation and conceptual experiments were carried out to evaluate the cooling performance thus enabled. In the system analysis, a thermal network model was established to characterize the thermal resistance of an ordinary high power LED light and that of the newly proposed light module. Through ventilating the high speed ambient airflow directly onto the chip surface, the thermal resistance of the whole light could be evidently reduced and additional pathway was thus opened for releasing heat from the chips. Further, three-dimensional finite volume simulations were adopted to investigate the temperature distribution of the new light. It was found that even without heat sink or active cooling at the back part of the LED light, the new method via cooling the front part still works well. Lastly, a conceptual experiment was performed, which again demonstrated that cooling the LED at its front surface suggests an effective way to maintain the safe running of LED light within an allowable temperature scale just as cooling the light at the back part. The present method initiates a new way for future thermal management of high power LEDs.

A liquid metal cooling system for the thermal management of high power LEDs

An active cooling solution using liquid metal as the coolant was proposed for high power light emitting diodes (LEDs). The typical thermal-physical properties of liquid metal were presented. Then a series of experiments under different operation conditions were performed to evaluate the heat dissipation performance of the liquid metal cooling system, and the results were compared with that of water. In order to better understand the cooling capability of liquid metal cooling system, a theoretical thermal resistance model was established and discussed. Both the experiments and theoretical analysis indicated that liquid metal cooling was a powerful way for heat dissipation of high power LEDs, and the fabrication of practical liquid metal cooling devices was feasible and useful.

Experimental and Numerical Investigation of a Microjet-Based Cooling System for High Power LEDs

The optical extraction efficiency and reliability of light emitting diodes (LEDs) relies heavily on successful thermal management due to their inherit dependence on the low junction temperature of LED chips. In this paper, a microjet-based cooling system is proposed for the thermal management of high power LEDs. Experimental and numerical investigations on such an active cooling system were conducted. Thermocouples were packaged with LED chips to conduct an online measurement of the temperature and evaluate the cooling performance of the proposed system. The experimental results demonstrate that the microjet-based cooling system has good cooling performance. For a 2 × 2 LED chip array, when the input power is 5.6 W and the environmental temperature is 28°C, the temperature of the 2 × 2 LED chip array reaches 72°C within 2 minutes and continues to increase sharply if no active cooling technique is applied. By using the proposed cooling system to cool the LEDs, however, the maximum LED temperature measured by thermocouples will remain stable at about 36.7°C, when the flow rate of the micropump is 9.7 mL/s. With consideration of the experimental difficulty, a numerical investigation was conducted on flow and temperature distribution in the microjet device. The feasibility of the numerical model was proven by comparison with experimental results. The numerical results showed that at a flow rate of 3.2 mL/s, the heat transfer coefficient of the impinging jets in the proposed system was about 5523 W/m2·K, and the pressure drop in the microjet device was about 1368 Pa.

A Microjet Array Cooling System for Thermal Management of High-Brightness LEDs

In this paper, a microjet-based cooling system is proposed for the thermal management of high-power light-emitting diodes (LEDs). Preliminary experimental investigation and numerical simulation on such an active cooling system are conducted. In the experiment investigation, thermocouples are packaged with LED chips to measure the temperature and evaluate the cooling performance of the proposed system. The experimental results demonstrate that the microjet-based cooling system works well. For a 2 times 2 LED chip array, when the input power is 5.6 W and the environment temperature is 28degC, without any active cooling techniques, the temperature of 2 times 2 LED chip array substrate reaches 72degC within 2 min and will continue to increase sharply. However, by using the proposed cooling system, when the flow rate of micropump is 9.7 mL/s, the maximum LED substrate temperature measured by the thermocouples will remain stable at about 36.7degC. As for the numerical optimization, the comparison between the simulation and experimental results is presented to confirm the feasibility of the simulation model. By using the simulation model, the effects of microjet diameter, top cavity height, micropump flow rate, and jet device material on system performance are numerically studied. According to the preliminary test and numerical optimization, an optimized microjet cooling system is fabricated and applied in thermal management of a 220-W LED lamp. The temperature test demonstrates that the cooling system has good performance.