LED lamps heat level to improve the proposed resolution

OFweek Semiconductor Lighting Reuters LED lighting fixture reliability (life) largely depends on the level of heat dissipation, so increasing the level of heat dissipation is one of the key technologies. Mainly to solve the problem that the chip generates excess heat through the heat sink and the heat sink, which is a very complicated technical problem.

The power of LED luminaires, which LEDs need to consider heat dissipation issues, power LEDs need heat dissipation. The power LED is a light emitting diode with an operating current above 100 mA. It is our country's line of reference with reference to the United States ASSIST Union definition, according to the existing two kinds of LED forward voltage typical values ​​of 2.1V and 3.3V, that is, input power at 210mw and 330mw above the LED are power LED, need to consider the device heat dissipation The problem, some people may have different views, but the practice has proved that to improve the reliability of the power LED (life), we must consider the power LED cooling problem.

The main parameters related to heat dissipation related to LED heat dissipation include thermal resistance, junction temperature and temperature rise.

Thermal resistance is the quotient of the difference between the effective device temperature and the externally specified reference point temperature divided by the steady state power dissipation in the device. It is the most important parameter that indicates the degree of heat dissipation of the device. At present, the thermal LED with better heat dissipation ≤10°C/W, the best thermal resistance reported in China is ≤5°C/W, and the thermal resistance in foreign countries is ≤3°C/W. If this level is achieved, the lifetime of the power LED can be ensured. .

The junction temperature refers to the temperature of the semiconductor junction in the main heat-generating portion of the LED device. It reflects the temperature value of LED devices under working conditions. For this reason, the US SSL program has set a goal to improve heat resistance. The heat resistance of chips and phosphors is still very high. At present, the junction temperature of the chip has reached 150°C. At 130°C, the phosphor has basically no effect on the life of the device. The higher the heat resistance of the chip phosphor, the lower the requirement for heat dissipation.

There are several different temperature rises in temperature rise. What we are talking about here is: Shell - Temperature rise in the environment. It refers to the difference between the temperature of the LED device package (the hottest point of the LED lamp) and the temperature of the environment (on the lighting plane of the lamp, 0.5 meters from the lamp). It is a directly measurable temperature value and can directly reflect the degree of heat dissipation of the LED device. It has been proved that when the ambient temperature is 30°C, if the measured LED bulb is 60°C, the temperature rise should be 30°C. At this time, the lifetime value of the LED device can be basically ensured. If the temperature rise is too high, the maintenance rate of the LED light source will be greatly reduced.

LED lighting new issues:

With the development of LED lighting products, there are two new technologies: First, in order to increase the luminous flux of a single tube, a greater current density is injected, as mentioned below, so that the chip generates more heat and needs heat dissipation. Second, to encapsulate new structures, as the power of LED light sources increases, multiple power LED chips need to be packaged together, such as a COB structure, a modular light fixture, etc., which will generate more heat and require a more effective heat dissipation structure and Measures, which in turn raise new issues for heat dissipation, otherwise it will greatly affect the performance and life of LED lamps.

At present, the total efficiency of heat dissipation of LED luminaires is only 50%, and there is still a lot of power to become hot. Secondly, LED high-current density and modular lighting fixtures will generate more concentrated waste heat and require good heat dissipation.

To improve heat dissipation, we provide the following suggestions:

1) From the perspective of LED chips, new structures and processes are needed to improve the heat resistance of the junction temperature of the LED chips, and the heat resistance of other materials, so that the requirements for heat dissipation conditions are reduced.

2) Reducing the thermal resistance of LED devices, adopting new packaging structures and new processes, selecting new materials with good thermal conductivity and heat resistance, including adhesive materials between metals, mixed plastics of phosphors, etc., resulting in thermal resistance ≤ 10°C/W or lower.

3) Reduce the temperature rise, use heat-dissipating materials with good thermal conductivity as far as possible, and require better ventilation channels in the design so that the residual heat can be dissipated as soon as possible and the temperature rise should be less than 30°C. In addition, raising the level of heat dissipation for modular luminaires should be mentioned on the agenda.

4) There are many ways to dissipate heat. If a heat pipe is used, it is of course very good. However, considering the cost factor, the cost-effectiveness should be considered when designing.

In addition, the design of LED lamps in addition to improving the efficiency of lamps, light distribution requirements, beautiful appearance, to improve the level of heat dissipation, the use of good thermal conductivity materials, it is reported that the heat sink coated with certain nano-materials, its thermal conductivity increased 30 %. In addition, to have good mechanical properties and tightness, the heat sink should also be dust-proof, requiring the temperature rise of LED lamps should be 30 °C smaller.