LED cooling technology

2018-12-13 00:00:00

LED heat dissipation technology was born in 2000, made of semiconductor light-emitting diodes (leds). Its working principle is radiation composite electroluminescence, which is the most common way of heat dissipation. Aluminum fins are used as part of the shell to increase the heat dissipation area.

• fever

Like traditional light sources, semiconductor light-emitting diodes (leds) generate heat during operation, depending on the overall luminous efficiency. Under the action of external electrical energy, the radiation of electrons and holes is combined to produce electroluminescence. The light emitted near the PN junction also needs to pass through the semiconductor medium and packaging medium of the chip itself to reach the outside world (air).Based on the comprehensive current injection efficiency, radioluminescence quantum efficiency and chip external light removal efficiency, only about 30-40% of the input electric energy is converted into light energy in the end, and the remaining 60-70% of the energy is mainly converted into heat energy in the form of non-radiation composite lattice vibration.

• impact on longevity

Generally speaking, whether the LED lamp works stably, the quality is good or bad, and the heat dissipation of the lamp body itself is very important. The heat dissipation of high-brightness LED lamps in the market often USES natural heat dissipation, and the effect is not ideal.LED lamps made by LED light source are composed of LED, heat dissipation structure, driver and lens, so heat dissipation is also an important part. If LED does not heat well, its life will be affected. Many people still think of the LED heat sink as a piece of aluminum with some leaves on it. The more blades you have, the more surfaces you have, the better the result. That's not the case.

1. Heat management is a major problem in the application of high-brightness LED

Since the p-type doping of group III nitride is limited by the solubility of Mg acceptor and the higher start-up energy of the holes, heat is particularly easy to be generated in the p-type region, and this heat must be dissipated on the heat sink through the whole structure. The heat dissipation way of LED devices is mainly heat conduction and heat convection. Sapphire substrate material's extremely low thermal conductivity leads to increased device thermal resistance, resulting in serious self-heating effects that have a devastating impact on device performance and reliability.

2. Influence of heat on high brightness LED

The heat is concentrated in the chip with small size. The temperature of the chip increases, which leads to the non-uniform distribution of thermal stress, and the decrease of luminous efficiency and laser efficiency of fluorescent powder. When the temperature exceeds a certain value, the device failure efficiency increases exponentially. Statistics show that the component temperature every 2 ℃, a fall of 10% reliability. The heat dissipation problem is more serious when multiple leds are densely arranged to form a white light lighting system. Solving the problem of heat management has become a prerequisite for the application of high-brightness LED.

3. The relationship between chip size and heat dissipation

The most direct way to improve the brightness of power LED is to increase the input power, and in order to prevent the saturation of active layer, the size of p-n junction must be increased accordingly. Increasing the input power will inevitably increase the junction temperature and thus decrease the quantum efficiency. The improvement of the power of a single tube depends on the device's ability to derive heat from the p-n junction. Under the condition of maintaining the existing chip material, structure, packaging technology, current density on the chip unchanged and equivalent heat dissipation, if the chip size is increased separately, the junction temperature will continue to rise.

• ways to dissipate heat

1. Aluminum radiator fin

This is the most common way of heat dissipation, using aluminum heat dissipation fins as part of the shell to increase the heat dissipation area.

2. Heat-conducting plastic shell

Using LED insulated heat dissipating plastic instead of aluminum alloy to make heat dissipating body can greatly improve the thermal radiation capacity.

3. Surface radiation treatment

Lamp case surface does radiative heat dissipation processing, simple daub radiative heat dissipation paint namely, can take heat away from lamp case surface with radiative means.

4. Aerodynamics

Use lamp casing appearance, make convection air, this is the method that strengthens heat dissipation with lowest cost.

5. The fan

The inside of the lamp case is strengthened by long-lived and high-efficiency fan, which has low cost and good effect. However, it is more troublesome to change the fan, and it is not suitable for outdoor use. This kind of design is relatively rare.

6. Heat pipe

The heat is transferred from the LED chip to the heat dissipating fin of the shell by heat pipe technology. In large lamps, such as street lamps and so on are common designs.

Liquid bubble

The transparent liquid with high thermal conductivity is filled into the bulb body by liquid bubble packaging technology. This is in addition to the principle of reflection, the only use of LED chip surface heat conduction, heat dissipation technology.

8. Utilization of lamp holder

In the household type of LED light with small power, the internal space of the lamp head is often used to put part or all of the driving circuit of heat into it. Can use the lamp head that has bigger metal surface so like screw mouth lamp head to come loose heat, because lamp head is close connect lamp base metal electrode and power line. So some of that heat can be exported to heat dissipation.

9. Application of heat conduction and heat dissipation

The purpose of heat dissipation of lamp shell is to reduce the working temperature of LED chip. Because the expansion coefficient of LED chip is very different from that of metal thermal conductivity and heat dissipation material commonly used by us, LED chip cannot be directly welded to avoid damage of LED chip by high and low temperature thermal stress. The latest high thermal conductivity ceramic material, thermal conductivity close to aluminum, expansion system can be adjusted to synchronize with LED chip. In this way, heat conduction and heat dissipation can be integrated to reduce the intermediate links of heat conduction.

• breakthrough in cooling technology

The existing ceiling hole lamp mostly USES aluminum with fins as the radiator. The heat dissipation effect of this kind of radiator is not ideal.

1. Break through the existing problem of unsatisfactory heat dissipation effect of aluminum radiator with fins

Existing smallpox hole lamp USES the aluminium material that takes finned piece mostly as radiator, the heat dissipation effect of this kind of radiator is not ideal, heat dissipation body can achieve taller temperature normally.

2. Insulation and heat dissipation plastics are used instead of aluminum alloy to make heat dissipation body

In 2009, South Korea has developed a kind of LED bioconductive plastic, which can increase the thermal radiation capacity 4-8 times while keeping the heat dissipation capacity equal to that of aluminum alloy.LED heat dissipation made of this heat dissipation material can greatly improve the overall heat dissipation effect.

3. Adopt the principle of liquid convection to provide a ceiling hole lamp with good heat dissipation performance

Use the heat that the coolant in the reservoir fluid tank that installs on lampshade absorbs from lampshade, use the natural convection between the two reservoir fluid tanks with different height at the same time, the heat that the coolant absorbs from lampshade sends out, make the lampshade of smallpox hole lamp gets very good cooling thereby.

4. Flexible rotation for easy installation

As a result of connecting the cooling fluid convection pipe between two liquid storage tanks has bellows structure, and the bellows structure can be telescopic and bending deformation, so it will not hinder the flexible rotation of the lampshade, but also facilitate installation.

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