It is known that the service life of LEDs directly depends on the quality of the material used in the semiconductor, as well as the ratio of the current of the device to the amount of heat generated. The light output is gradually reduced, and after it will be half of the original value, the life of the LED will begin to decrease. The duration of the devices can be up to 100,000 hours, but only on condition that it is not affected by high temperatures.
To cool heat-generating devices, a device such as a radiator for LEDs is used in radio electronics. Heat removal from the units to the atmosphere is achieved by two methods.
The first way to cool LEDs
This method is based on the emission of thermal waves into the atmosphere, or thermal convection. The method relates to the category of passive cooling. Part of the energy enters the atmosphere with a radiant infrared stream, and part leaves through the circulation of heated air from the radiator.
Among the technology for LEDs, a passive cooling circuit is most widespread. It does not have rotating mechanisms and does not require periodic maintenance.
The disadvantages of this system include the need to install a large heat sink. Its weight is quite large, and its price is high.
Second method
It is called turbulent convection. This method is active. In this system, fans or other mechanical devices that can create air currents are applicable.
The active cooling method has a higher level of performance than the passive method. But adverse weather conditions, the presence of a large amount of dust, especially in the open space, do not allow installing such schemes everywhere.
The manufacture of radiators
When choosing a material should be guided by the following rules:
- The thermal conductivity should be at least 5-10 watts. Materials with a lower rate cannot transfer all the heat that the air receives.
- The level of thermal conductivity above 10 W from a technical point of view will be excessive, which will entail unnecessary money costs without increasing the efficiency of the device.
For the production of radiators, as a rule, aluminum, copper and ceramics are used. They produce devices based on plastic that dissipates heat.
Aluminum fixtures
The most popular radiator for LEDs is made of aluminum. The main disadvantage of the device is that it consists of a number of layers. This inevitably causes transient thermal resistances, the overcoming of which is possible through additional heat-conducting materials: substances on the adhesive, insulating plates, materials for filling the air gaps.
Aluminum heatsink for LEDs is used more often than others. It is prone to pressing and copes well with heat dissipation.
For the active level of cooling, as a rule, a flat sheet of aluminum is required, the size of which is no larger than the size of the lamp. The sheet is blown by a fan.
A suitable temperature for the functioning of the LED is considered to be 65 ° C. However, the lower the temperature, the higher the level of efficiency of the device and the longer its life. The optimal temperature of the surface of the radiator is considered an indicator of 45 ° C, but not higher. For a 1 W diode, it is necessary to install on an aluminum radiator. The area of the radiator is 30-35 cm 2 . The radiator of the 3 W LED will require a doubling of the area and will be 60-70 cm 2 .
As a radiator, an aluminum device is best suited as the lightest and relatively inexpensive. When calculating the device for LED matrices, a proportion of 35 cm per 1 W. is taken.
For active cooling systems, the radiator area may be less than 10 times. On the LED 1 W, 3-3.5 cm 2 is enough.
For example, consider a star radiator for LEDs. The device is used to remove heat from the LED and is a small radiator. Its basis is a plate made of a composite material - aluminum is used, which removes heat from the LED, and a copper foil with contact pads. The radiator is mounted on LEDs with a high power rating (1-3 W).
Copper radiators
Devices contain a copper plate. Copper has a higher thermal conductivity than aluminum. Its inclusion in the scheme is justified.
But in general, metal is inferior to aluminum in terms of weight and technical characteristics. Copper is not a ductile metal. The manufacture of a copper device by extrusion is economical. A sharp cutting leaves a large amount of waste expensive material.
Ceramic Radiators
A successful model is a ceramic radiator for LEDs, on which current-conducting paths are initially applied. Directly to them, the LEDs are soldered. This design leaves heat twice as much compared to aluminum devices.
Plastic radiators
Heat dissipating devices made of plastic are of particular interest. And this is understandable, since the cost of this material is lower than the price of aluminum, and the level of manufacturability is higher.
But the level of thermal conductivity of ordinary plastic is not higher than 0.1-0.2 W / (m · K). It is possible to achieve an acceptable indicator with the help of different fillers. When replacing an aluminum radiator with a device based on plastic (of equal size), the temperature level in the temperature supply region rises by 4-5%. Based on the fact that the thermal conductivity of a heat-dissipating plastic is lower than that of aluminum (8 W / (m · K) versus 220-180 W / (m · K)), we conclude: plastic can compete with aluminum.
Design features of radiators
Many people ask: which radiator is better for an LED?
There are two groups of modifications:
For example, the radiator for the 10W LED is represented by a ribbed LED device.
The first type, as a rule, is used for the natural method of cooling LEDs, and the second for forced. With the same dimensions, the passive needle device is 70% more efficient than the ribbed type.
Radiators for high-power LEDs are needle-shaped. They are designed for powerful LEDs, but this does not mean at all that ribbed devices based on plates are suitable only for functioning together with a fan. Depending on the geometric parameters, they are also used for passive cooling.
The radiator for LEDs of any configuration can have a square, rectangular or round shape.
How to calculate the area of the radiator. Methods for obtaining accurate indicators of device parameters
In this case, a number of important factors are taken as a basis:
- indicators of air;
- diffusion area level;
- radiator modification;
- Features of the material of which the heat exchange device is made.
But all these nuances are needed for the designer who is involved in the development of the heat sink.
As a rule, amateur radiators are taken as the basis for ham radio. All that is required is a knowledge of the maximum power dissipation indicator of the heat exchanger.
First method
The calculation of the area is carried out according to the formula F = a x Cx (T1 - T2), where is the heat flux, and S is the surface area of the radiator (the sum of the areas of all the fins or needles and the substrate in sq. M), T1 is an indicator of the temperature of the medium that takes away heat, and T2 - temperature of the heated surface.
When calculating the area, you should pay attention to the fact that the rib or plate has two surfaces for heat dissipation.
The needle surface is calculated along the circumference (π x D) times the height indicator.
For surfaces that have not been polished, the heat transfer coefficient is an indicator equal to 6-8 W / (m 2 · K).
Second calculation method
There is another simple formula that is obtained through experimentation.
S = [22 - (M x 1.5)] x W, where S is a measure of the area of the heat exchanger, W is the summed power (W), and M is the idle power of the LED.
For the fin type radiator made on the basis of aluminum, you can use the data provided by engineers from Taiwan. The data do not have accuracy, since they are indicated in ranges with a large take-off indicator. In addition, the definition is suitable for the climatic conditions of Taiwan. They can be taken as a basis only during preliminary calculations.
How to make a radiator with your own hands?
Hams are rarely accepted for the manufacture of heat sinks with their own hands, since this element requires special responsibility. After all, this device has an effect on the long-term service of the LED. But it so happens that the masters resort to the manufacture of a heat exchanger from improvised means.
First option
The design is unified. It is a circle that is cut out of aluminum. It has incisions. The resulting sectors are slightly bent. The result is a part similar to a fan impeller. Four antennae are bent along the device’s axes, which serve as a device mount. The LED can be fixed by thermal paste and self-tapping screws.
Option 2
Do-it-yourself radiator for LEDs can be made from a fragment of an aluminum pipe with a rectangular cross section.
Materials needed:
- pipe size 30x15x1.5 mm;
- a press washer whose diameter is 16 mm;
- thermal glue;
- KTP-8 thermal paste;
- Sh-shaped profile 265;
- self-tapping screws.
To optimize the convention, three holes are drilled, the diameter of which is 8 mm, and in the profile there are holes with a diameter of 3.8 mm for fasteners using self-tapping screws.
LEDs are glued to the pipe - the main part of the radiator - using thermal glue. In places where the radiator parts are connected, a layer of thermal paste KTP-8 is applied.
Then proceed to the assembly of the structure using self-tapping screws with a press washer.
Methods for attaching LEDs to a radiator
LEDs are attached to the device using two methods:
Glue LED thermal glue. To this end, a little glue is applied to the metal surface, then an LED is placed on it. To obtain a good connection, the LED is pressed with a load until the adhesive completely dries. But most masters prefer to use the mechanical method.
Currently, special panels are being manufactured, through which it is possible to mount the diode as soon as possible. Some models provide additional clips for secondary optics. Installation is very simple. An LED is installed on the radiator, then on it is a panel that is attached to the base with self-tapping screws.
Conclusion
The cooling radiator for high-quality LEDs has become the key to the durability of the device. Therefore, when choosing a device, you should be extremely careful. It is better to resort to the use of factory heat exchangers. They are available at radio stores. The cost of the devices is high, but the installation of the LED on them is easy, and the protection is distinguished by quality and reliability.