Three volt days high temperature difficult to block, how to solve the LED heat dissipation?

Date:30-08-2019

"Three volt days" high temperature difficult to block, […]

"Three volt days" high temperature difficult to block, how to solve the LED heat dissipation?

A few days ago, abnormal high temperatures occurred all over the country.High temperature has a great impact on human body. What about LED light source?

As we all know, the energy added by LED in working state is not all converted into light energy, but part of it into heat energy. As the fourth generation light source, LED has great prospects for development because of its advantages of energy saving, environmental protection and long life. But LED is very sensitive to temperature. The increase of junction temperature will affect the lifetime, light efficiency, light color (wavelength), color temperature, light shape (light distribution), forward voltage, maximum injection current, luminosity, chroma, electrical parameters and reliability of LED.
First of all, high temperature will cause permanent damage to the LED. When the temperature of the LED exceeds the load temperature of the chip, the luminous efficiency of the LED will decrease rapidly, resulting in obvious light decay and damage. In addition, most of the LEDs are encapsulated in transparent epoxy resin. If the junction temperature exceeds the solid phase transition temperature (usually 125 C), the packaging materials will change to rubber shape and the thermal expansion coefficient will rise sharply, which will lead to the open circuit and failure of the LED.

Secondly, higher temperature will shorten the lifetime of LED. The lifetime of the LED is reflected in its light decay, that is, the brightness becomes lower and lower over a long period of time until it finally goes out. Usually, the lifetime of LED is defined as the time when the luminous flux decreases by 30%. The defects in the materials of LED chips will multiply and multiply rapidly at high temperature until they invade the luminous region and form a large number of non-radiative composite centers, which seriously reduces the luminous efficiency of LED. In addition, at high temperatures, micro-defects in materials and fast-spreading impurities from interfaces and panels will also introduce into the luminous region, forming a large number of deep levels, which will also accelerate the optical decay of LED devices. At the same time, transparent epoxy resin will denaturate and yellowing at high temperature, which will affect its light transmission performance. The higher the working temperature, the faster this process will proceed, which is another main reason for the light decay of LED. In addition, the optical decay of phosphors is also a major factor affecting the optical decay of LED, because the attenuation of phosphors at high temperature is very serious.

Heat dissipation is the main obstacle in the development of LED as a lighting object, so reducing the temperature of LED by various means has become a major issue discussed by major manufacturers. As the heat dissipation of LED is becoming more and more important, various heat dissipation technologies are also applied to LED lighting technology.
Because the LED light source itself has no radiation heat dissipation function, the heat dissipation way of the LED lighting lamps can only be derived through the radiator which is closely combined with the LED lamp bead board. Any radiator, in addition to being able to quickly transfer heat from the source of heat to the surface of the radiator, the most important thing is to rely on convection and radiation to dissipate heat into the air. Heat conduction only solves the way of heat transfer, and heat convection is the main function of the radiator. The heat dissipation performance is mainly determined by the heat dissipation area, shape and the ability of natural convection intensity. Thermal radiation is only an auxiliary role.

Radiator, as a common way of heat dissipation for LED lamps, its shape and material have also undergone a series of changes. At present, there are several kinds of LED radiators on the market: die-casting aluminum radiator, extrusion aluminum radiator, stamping aluminum radiator, plastic-clad aluminum radiator and high thermal conductivity plastic radiator.
The production cost of die-casting aluminium radiator is controllable, and the radiator fin can not be thin, so it is difficult to maximize the radiation area. Extruded aluminium radiator fins can be made many thin, the maximum expansion of the radiation area, radiation fins work automatically to form air convection diffusion heat, heat dissipation effect is better, but later processing costs are higher. Stamping aluminium radiator is a cup-and-tube type radiator by punching and drawing steel and aluminium alloy sheets with punch and die. The exterior and interior of the stamping radiator are smooth, and the heat dissipation area is limited due to the absence of wings. The thermal conductive plastic used in plastic-clad aluminium radiator is a kind of thermoplastic material. Its fluidity, density, toughness and strength are easy to be injection moulded. It has good cold and thermal shock resistance, excellent insulation performance, low processing cost, short processing cycle and low processing temperature compared with all aluminium radiator. Customer-owned injection moulding machine can design and produce different shapes of lamps and lanterns. Plastic-clad aluminium radiator has good insulation performance and easy to pass through safety regulations. High thermal conductivity plastic radiator, high thermal conductivity plastic radiator is a kind of all-plastic radiator. Its thermal conductivity is tens of times higher than that of ordinary plastics, and it has excellent heat conduction and radiation ability. It can be used as a new type of insulating heat dissipation material for various power lamps and lanterns.

In recent years, with the wider and wider application of LED lighting, the LED lighting industry has developed rapidly, and the division of labor has also made considerable progress. LED lamps manufacturers with channel advantages purchase heat dissipation components, LED light source and driving power from suppliers respectively, and then assemble them into finished lamps and sell them to their downstream customers. The growing demand of customers such as lighting manufacturers promotes the sustainable development of LED lighting heat dissipation components industry.
LED lighting applications and heat dissipation technology requirements are different, so that the LED lighting heat dissipation components industry presents different competitive characteristics.

Low power LED lighting products have low power consumption and calorific value, mainly depending on the heat dissipation of the lamp shell. There are a large number of lighting or hardware processing enterprises engaged in small-power LED lighting products and lamp shell processing. The production is relatively scattered, and the number of enterprises with large-scale supply capacity is relatively small. The rapid increase in market penetration of low-power LED lighting products has also attracted a large number of home-based workshop enterprises into the field of low-power LED lamps processing, which has intensified the competition in this industry. At present, the majority of enterprises in low-power LED lighting heat dissipation module industry have low technology level, relatively backward manufacturing technology, and pay little attention to the design of heat dissipation of lamps and lanterns, and the quality of products is not high. These enterprises mainly participate in the competition of low-end products.
High-power LED lighting products have a variety of specifications, mainly as energy-saving alternatives to traditional metal halide lamp, high-pressure sodium lamp and other lighting sources, and are currently in the market lead-in period. It is expected that with the progress and popularization of heat dissipation technology and the outbreak of high-power LED lighting market, more and more enterprises will enter the field of heat dissipation of high-power LED lighting, and the competition will become increasingly fierce.

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