SMD LED matrix. LED matrices. Short operating time
LED matrices are a technological combination of several light-emitting semiconductor crystals on one substrate, with a common filling with a mixture of phosphor and silicone.
The appearance of LED matrices is associated with the development of (Chip-on-Board), which literally translates as “chip on a board.” This technology has replaced SMD LEDs, is characterized by a high degree of production automation and has led to a significant reduction in prices for LED lamps and spotlights.
Types and applications
While maintaining the same principle of placing LED crystals on a heat-conducting substrate, LED matrices differ significantly in the number of crystals on one base and the methods of connecting them to each other.
The number of crystals on one substrate determines the final power of the matrix, which can reach hundreds of watts per product. Powerful matrix light sources have proven themselves in floodlights and street lighting fixtures. The way the crystals are connected to each other determines the ability to control the glow of individual crystals and the parameters of the power supply for the matrix. The series-parallel structure of internal connections makes it possible to reduce the current and increase the supply voltage, which is reflected in the characteristics of matrix products.
Another feature of the internal connections of crystals with external pins is the possibility of using LED matrix structures in information displays and in graphic or character screens. Such LED matrices find their application in control and measuring equipment and all kinds of advertising installations. 
In outdated models, for information displays, graphic or character screens, LED matrices were designed based on DIP or SMD LEDs.
Schematic diagram
As noted above, the series-parallel circuit for connecting LED crystals to each other determines the requirements for the power supply of the matrix. The higher the supply voltage, the more LEDs are combined in series circuits. 
This feature reduces the requirements for the output currents of the drivers, but if one crystal in a series circuit fails, the entire chain stops emitting light. The current is redistributed to the working LED chips, thereby accelerating their degradation and seriously reducing the service life of the LED matrix as a whole.
To solve the problem, some manufacturers connect all the LED chips inside the matrix simultaneously in series and in parallel. This feature significantly reduces the possibility of failure of the LED matrix due to the burnout of one chip. 
Parallel connection of LEDs to each other within the same matrix structure requires large output currents of the driver, but the overall emissivity practically does not suffer from the failure of one or two crystals. 
Matrices for LED displays incorporate a complex internal switching system, which is determined by the requirements for controlling each LED individually. To control such LED matrices, special integrated processors and microcircuits have been created. 
Connection
In the connection diagrams of LED matrices, the determining factors for their reliability are two key points - sufficient radiator area for heat removal and stabilization of supply currents. Both of these factors are directly related to the increased degradation of semiconductor crystals when their temperatures exceed the maximum permissible.
An increase in the temperature of the crystal is caused by both insufficient area of the cooling radiator and too high passing current.
The operating values of direct current are indicated in the parameters of the LED matrices, and for an approximate selection of the radiator area, you can use the figure 20-25 cm² per 1 W of matrix power. It should be taken into account that such an area is necessary at ambient temperatures up to 35 °C. At higher temperatures, the working area of the radiator should be increased or supplemented with active cooling.
When choosing LED matrices with a built-in driver and power supply from a 220 V network, it is necessary to take into account that such light sources are not suitable for illuminating places where people permanently reside.
The absence of high-capacity electrolytic capacitors in the driver circuit powered by a 220-volt network determines the high emitted light, the harmful effect of which on human health has been proven by many scientific studies.
Conclusion
Improving the parameters of light-emitting LED crystals leads to the emergence of increasingly powerful matrix structures, the output power of which has already reached 300 W or more.
This trend, combined with an increase in the specific luminous flux per 1 W of supplied power, determines the further development of LED matrices and their rapid development in the lighting equipment market.
Read also
It is believed that one of the most effective ways to generally reduce energy costs today is to organize artificial lighting systems using LEDs.
With the same luminous flux, the energy consumption of LED light sources is approximately 10 times lower than that of a conventional incandescent lamp. At the same time, they last many times longer than fluorescent lamps.
Until recently, the widespread use of LED lamps was hampered by their high price, which is largely determined by the rather complex manufacturing technology. So, in order to install a single crystal on a substrate (printed circuit board), soldering is used in a convection oven.
To reduce the labor intensity of manufacturing energy-saving light sources, LED matrices were developed, which in general are a set of single LEDs with a common (parallel connection) or separate power supply.
In this case, about 9 or more crystals are mounted on one substrate, which are then filled with phosphor.
This technology has significantly reduced the cost of manufacturing LED lamps and made them more accessible. Such matrices are successfully used in the manufacture of both lighting devices and display devices. They do not require soldering in a convection oven; they can be installed manually or using special mounting modules.
SMD diodes(Surface Mounted Device) is a somewhat outdated type, structurally consisting of a metal substrate (copper or aluminum) on which a crystal is mounted, soldered to the contacts of the case where the substrate is installed.
The crystal is covered with a lens and/or coated with a phosphor. This technology makes it possible to place up to three LEDs on one substrate. They are used in the production of LED strips for lighting and illumination.
Moreover, depending on the number of crystals in the matrix, strips with a number of LEDs of 60 pcs/m (1 crystal) and 30 pcs/m (3 crystals) are produced. The brightness of strips with LEDs consisting of three crystals is naturally higher than that of strips with LEDs on one crystal.
SMD matrices are also available with crystals having different glow colors (RGB type). RGB LEDs are controlled by special controllers that regulate the brightness or power of the light using the pulse width modulation (PWM) method.
By applying a current of varying magnitude to each colored crystal, you can change its overall luminous flux, creating bizarre combinations of colors and brightness.
SOV diodes(Chip On Board) is the most common type of matrix LEDs. Structurally, they represent a substrate (board) on which a large number of unpackaged crystals are mounted. Then they are filled with phosphor.
A large number of crystals ensures increased brightness of SOV type LEDs, which is an order of magnitude higher than that of SMD type diodes. SOV type diodes are used both for lighting and as indicating devices.
Filament LEDs promising Chip On Glass technology, which allows you to install 28 crystals on a glass or sapphire substrate.
Used in the manufacture of LED lamps in transparent glass flasks. At the same time, the luminous flux extends over 360°, which makes it possible to obtain greater illumination with the same power as SMD and SOV LEDs.
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Let's express our point of view on this dilemma, which is beginning to resemble a debate about which is better, iOS or Android. There is no clear answer to this question. It is necessary to clearly understand the purpose of the lamp, which uses a diode matrix. For some, COB will be better, for others - SMD.
COB for low power downlights
For example, COB clearly wins in commercial directional lighting fixtures. Such as track lights, downlights and other types of accent lighting.
For diffuse commercial lighting, a conventional LED strip or ruler mounted around the perimeter of the lamp body under the diffuser is more suitable. COB matrices also behave quite well in street floodlights with a power of up to 50 watts.
SMD for industrial dome lights over 50W
As for the lighting of industrial enterprises, for example, in industrial LED lamps the bell
It is almost impossible to find a COB matrix (see figure on the right) from world-famous advanced manufacturers, although a few years ago everyone loved such experiments.
Industrial LED dome lamps with a COB matrix are much cheaper than a lamp with an SMD diode board, such as industrial dome lamps.
This is due to the fact that a COB matrix with diodes from the same manufacturer costs 30-50% less, which reduces the cost of the lamp. The downside, according to reviews from most well-known manufacturers of industrial and street lighting, is the frequent replacement of COB matrices under warranty if the lamp power is more than 50 W.
At one of the factories with which we cooperate, we were told a story about how an industrial LED bell lamp with a high-quality heat dissipation system and a high-quality COB diode was left turned on with the chip down on the table, and within 2 hours the table caught fire.
Real experience
From our personal practice, we know the story of how a power engineer at a large enterprise, in order to save money at the expense of quality, bought industrial dome lamps with COB diodes and now he has to pay for his wrong decision: every year to change the diode boards in 15-20% of the lamps .
In order not to get scolded by his superiors for making the wrong choice at one time, he asks to be billed for fluorescent lamps and various electrical consumables instead of COB matrices, in order to hide real expenses.
COB Diode Degradation
We should also not forget about the real degradation of diodes in high-power industrial luminaires, which, according to user observations, is higher for high-power luminaires with COB elements. But very rarely does anyone carry out annual measurements of room illumination.
Glare effect of COB diodes
Another observation from users is the fact that industrial LED dome lights with COB matrix in warehouses and workshops give a stronger glare effect, which makes it difficult for personnel to work at heights.
Expert opinion: “Our opinion: COB LED luminaires are the best solution for accent lighting and moderate power luminaires up to 50W. The only exceptions are multi-module systems, in which each module is a separate COB matrix of moderate power. For lighting of more than 50 watts, it is better to use industrial bell lamps with an SMD matrix. Moreover, the greater the number of diodes per 1 watt of power, the better,” says Alexey Frolov, lighting engineer at Grandenergoproekt.
Knyazev O.V., Stroy-TK Group of Companies, May 2017
Currently, the LED lighting market in Russia is experiencing a boom; both high-tech expensive models of lamps and spotlights are on sale, the warranty period for which is 3-7 years, as well as cheap LED products that are unlikely to work without breakdowns for at least 1 year. Let's try to make sense of this multitude of proposals.
Where do cheap disposable “crafts” come from?
Paradoxically, the presence of a large number of offers of cheap consumer-grade LED lamps is the fault of the Customer himself, because the main selection criterion for the Customer is Cost.
The situation is repeating itself, as it happened before: if there is a demand for cheap products, manufacturers from the Middle Kingdom will provide supply! Since no one has a monopoly on imports from China, competitors are beginning to demand that manufacturers constantly, from batch to batch, reduce purchase prices in order to simply beat out competitors in the market with a low price. However, there are reasonable limits to everything and a constant reduction in the cost of products while maintaining all the basic characteristics is simply impossible. So the game begins to reduce performance characteristics, reliability, etc. - just to sell lighting equipment, providing a minimum warranty period. And this despite the fact that crazy operating times are announced for LEDs - from 50 to 100 thousand hours.
What is COB
COB technology, more recently MCOB (Multi Chip-on-Board) - translated as “Crystal on a Board”. Considered to be the most advanced LED technology to date.
Briefly, it can be described as follows: placing crystals on a board without housings and ceramic substrates, as well as covering all these crystals with a common layer of phosphor. LED crystals are located very close to each other - the placement density can reach 70 crystals per 1 cm 2, i.e. the crystals practically merge into a single field and the glow of the matrix is very uniform, individual points of the crystals are indistinguishable.
An important advantage of the technology is the quality of the emitted light. Objects illuminated by COB-matrix lamps have a clear shadow boundary due to the uniform distribution of the light flux. Lamps based on SMD LEDs, unfortunately, cannot boast of such contrast due to the large number of individual crystals and reflectors widely spaced in space.
The energy efficiency of COB matrices can reach 170 Lm/W.
Benefits of COB
The main advantages of MCOB technology are:
- High luminous efficiency (more than 100 lm/W);
- Possibility of achieving high luminous flux intensity with relatively small dimensions;
- Compatible with various drivers, incl. with dimming;
- Uniformity of light flux, absence of shadow effect;
- Compactness, small size, availability of various shapes;
- Possibility of producing matrices of any color temperature from 2700K to 7000K;
- Color rendering index up to 90Ra;
Disadvantages of COB
The main disadvantage of COB technology is the mandatory provision of good heat removal from a powerful COB matrix, which is difficult to ensure, since the matrix area is small, and it is difficult to remove excess heat from a small contact area.
This is where the catch lies: a cheap, and therefore initially low-quality, COB matrix, mounted on a cooling radiator without proper fitting and processing of the mating surfaces, does not cool enough, begins to overheat and, ultimately, burns out.
As confirmation, we can cite the following fact: not long ago, our service center received 57 LED floodlights (COB) with a power of 100 W for diagnostics and repair. Judging by their appearance (see photo), they are from the cheap GS Light series.
After diagnostics, it was revealed that in the vast majority of spotlights (49 pieces), the COB LED matrix failed, and in the remaining 8 cases, the LED driver failed.
What is SMD
SMD (Surface Mounting Device) technology can literally be translated as “surface mounted device”.
The main difference between this technology and the "traditional" through-hole technology is that the components are mounted on the surface of the board. This ensures smaller design dimensions, better heat dissipation, and design variability. This design is the most common in lighting today and is used in almost all types of light sources.
Today, SMD technology is the most common in LED lighting and is used in almost all types of lamps.
This technology was created to organize powerful diffused lighting, which is achieved by distributing a significant number of small LEDs over the entire area of the lamp (there are up to 700 pieces in one product), which makes it possible not to use any additional optics in the lamps, only the usual protective glass of the housing lamp To increase the degree of dispersion (for example, for rooms with computer equipment), a milky, prismatic or microprismatic diffuser is used.
Since the LEDs are located on a large aluminum strip, and the distance between them is quite large, cooling the LEDs does not cause much difficulty, hence the durability of SMD strips if they are properly powered.
Among the disadvantages of lamps with SMD lines, it should be noted that they are very difficult to repair, since when one LED fails, the entire line stops lighting, and replacing an SMD LED yourself is a rather labor-intensive task. Replacing the entire line is already financially expensive. To be fair, it must be said that most manufacturers of LED lamps in Russia, when a warranty case arises, replace the entire line.
COB and SMD Applications
1. General case
I would make the section this way: if the form factor of the lamp body allows you to place a sufficiently large cooling radiator, then you can use COB LED lamps, limiting their power to 30 W. All lighting equipment with higher power is exclusively SMD. In general, the ideal option for introducing LED lighting would be.
2. I handed over the object and forgot
If the task is precisely this - to hand over the object and run away, then, of course, you need to use cheap lamps or spotlights on a high-power COB matrix. The time they work should be enough for you to disappear from sight... :)
3. Short working time
If a lamp or spotlight works occasionally, turning on for a few minutes (for example, it is equipped with a presence sensor and turns on only when people pass), you can safely choose COB. The matrix simply will not have time to overheat.
4. Organization of temporary lighting.
To organize temporary lighting (for example, at a construction site during finishing work), I would recommend using COB floodlights with a power of 20 - 30 W.
5. Lighting for warehouses and industrial premises
In warehouses, industrial buildings and premises, powerful lamps suspended at a high (6-12 meters) height are usually used. For their electric lighting, it is strongly recommended to use lamps made on SMD LED strips. When choosing lamps, pay special attention to the presence of clearly visible radiators, the purpose of which is to dissipate excess heat into the environment.