LED matrix. led matrix smd led matrix

It is believed that one of the most effective ways to reduce overall energy costs today is the organization of artificial lighting systems using LEDs.

With the same luminous flux, the power consumption of LED light sources is about 10 times lower than that of a conventional incandescent lamp. At the same time, they serve many times longer than fluorescent lamps.

Until recently, the mass use of LED lamps has been constrained by their high price, which is largely determined by a 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 complexity of manufacturing energy-saving light sources, LED arrays were developed, which in the general case 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 a phosphor.

This technology has significantly reduced the cost of manufacturing LED lamps and made them more affordable. Such matrices are successfully used in the manufacture of both lighting fixtures and indicating devices. They do not require soldering in a convection oven and can be mounted manually or using special mounting modules.

SMD Diodes(Surface Mounted Device) is a somewhat obsolete 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 backlighting.

At the same time, depending on the number of crystals in the matrix, tapes are produced with the number of LEDs 60 pcs/m (1 crystal) and 30 pcs/m (3 crystals). The brightness of the glow of tapes with LEDs, consisting of three crystals, is naturally higher than that of tapes with LEDs on a single chip.

SMD matrices are also available with crystals that have a different glow color (RGB type). RGB type LEDs are controlled by special controllers that adjust the brightness or power of the glow using the pulse-width modulation (PWM) method.

By applying a current of different magnitude to each colored crystal, you can change its total luminous flux, creating bizarre combinations of colors and brightness of the glow.

COB Diodes(Chip On Board from the English "chip on the board") is the most common type of matrix LEDs. Structurally, they are a substrate (board), on which a large number of unpackaged crystals are mounted. Then they are filled with a phosphor.

A large number of crystals provides an increased brightness of COB type LEDs, which is an order of magnitude higher than the similar parameter of SMD type diodes. SOV-type diodes are used both for lighting and as indicating devices.

Filament LEDs promising technology Chip On Glass, 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 spreads over 360 °, which makes it possible to obtain greater illumination at the same power as SMD and COB LEDs.

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Let's express our point of view on this dilemma, which is starting to resemble an argument about which is better, iOS or Android. There is no single 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 spotlights

For example, COB clearly wins in commercial spotlights. Such as track lights, downlights and other types of accent lighting.

For diffusing commercial lighting, a regular LED strip or a ruler mounted around the perimeter of the luminaire body under the diffuser is more suitable. COB matrices do not behave badly in street spotlights 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 meet a COB-matrix (see the figure on the right) from world-famous advanced manufacturers, although a few years ago everyone loved such experiments.

Industrial COB LED dome luminaires are much cheaper than SMD diode board luminaires such as industrial dome luminaires.

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 luminaire. The downside is, according to the reviews of most eminent manufacturers of industrial and street light, frequent replacements of COB matrices under warranty if the luminaire power is more than 50 watts.

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 forgotten with the chip turned on on the table down, and in 2 hours the table ignited.

Real experience

From our personal experience, we know a story about how a power engineer at a large enterprise, in order to save money at the expense of quality, bought industrial dome luminaires with COB diodes and now he has to pay for his wrong decision: every year to change diode boards in 15-20% of luminaires .

In order not to get scolded by his superiors for having made the wrong choice in his time, he asks him to bill him for fluorescent lamps and various electrical consumables instead of COB matrices in order to hide the real costs.

Degradation of COB diodes

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 someone makes annual measurements of the illumination of the room.

Blinding effect of COB diodes

Another user observation is the fact that industrial COB LED dome lights in warehouses and workshops produce more glare, making it difficult for personnel to work at height.

Expert opinion: “Our opinion: COB LED luminaires are the best solution for accent lighting and luminaires with moderate power up to 50W. The only exceptions are multi-module systems, in which each module is a separate COB matrix of moderate power. For lighting more than 50 watts, it is better to use industrial bell lamps with an SMD matrix. Moreover, the more diodes per 1 watt of power, the better,” says Alexei Frolov, lighting engineer at Grandenergoproekt.

LED matrices are a technological combination on one substrate of several light-emitting semiconductor crystals, with a common filling with a mixture of phosphor and silicone.

The appearance of LED matrices is associated with the development (Chip-on-Board), which literally translates as "a chip on the 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

Retaining a single principle of placing LED crystals on a heat-conducting substrate, LED arrays differ significantly in the number of crystals on one base and in the ways they are connected 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 spotlights and luminaires for street lighting. 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 magnitude of the supply voltage, which is reflected in the characteristics of matrix products.

Another feature of the internal connections of the crystals to each other with external leads is the possibility of using LED matrix structures in information boards and in graphic or character screens. Such LED-matrices are used in control and measuring equipment and various advertising installations.

In older models, for information boards, graphic or character displays, LED matrices were designed based on DIP or SMD LEDs.

circuit diagram

As noted above, the series-parallel circuit for connecting LED crystals to each other determines the requirements for the matrix power supply. The higher the supply voltage, the more LEDs are connected in series circuits. This feature reduces the requirements for the output currents of the drivers, but in the event of a failure of one crystal in a serial circuit, the entire circuit ceases to emit light. The current is redistributed to the working LED chips, thereby accelerating their degradation and seriously reducing the life of the LED matrix as a whole.

To solve the problem, some manufacturers connect all the LED chips inside the matrix at the same time 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 among themselves 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 system of internal switching, 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 schemes for connecting LED matrices, two key points are the determining factors for their reliability - a sufficient area of ​​\u200b\u200bthe radiator for heat removal and stabilization of the supply currents. Both of these factors are directly related to the enhanced degradation of semiconductor crystals when their temperatures exceed the maximum allowable.

Both the insufficient area of ​​the cooling radiator and the too high passing current lead to an increase in the temperature of the crystal.

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 required 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 powered by a 220 V network, it must be taken into account that such light sources are not suitable for illuminating places of permanent residence of a person.

The absence of high-capacity electrolytic capacitors in the driver circuit powered by 220 volts 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 more and more 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 input power, determines the further development of LED matrices and their outstripping development in the lighting technology market.

Read also

Knyazev O.V., Stroy-TK Group of Companies, May 2017

Currently, the LED lighting market in Russia is experiencing its boom, both high-tech expensive models of lamps and spotlights are on sale, the warranty period for which is 3-7 years, and cheap LED products that are unlikely to work without breakdowns for at least 1 year. Let's try to understand this set of proposals.

Where do cheap disposable "crafts" come from?

Paradoxical as it may seem, the Customer himself is to blame for the presence of a large number of offers of cheap consumer-grade LED lamps, because the main selection criterion for the Customer is the Cost.

The situation is repeating itself, as it was before with: if there is a demand for cheap products, manufacturers from the Middle Kingdom will also provide supply! Since no one has a monopoly on imports from China, competitors begin to demand from manufacturers a constant, batch by batch, reduction in purchase prices in order to simply score 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, reliability, etc. - just to sell lighting equipment, putting a minimum warranty period. And this despite the fact that for LEDs announced crazy operating time - from 50 to 100 thousand hours.

What is COB

COB technology, more recently MCOB (Multi Chip-on-Board) - translates as "Crystal On Board". It is considered the most advanced LED technology to date.

Briefly, it can be described as follows: placing crystals on the board without cases and ceramic substrates, as well as covering all these crystals with a common phosphor layer. 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 turns out to be very uniform, individual points of the crystals are indistinguishable.

An important plus of the technology is the quality of the emitted light. Objects illuminated by lamps on the COB-matrix have a clear shadow border due to the uniform distribution of the light flux. Lamps on SMD LEDs, unfortunately, cannot boast of such a contrast due to the large number of individual crystals and reflectors that are widely separated in space.

The energy efficiency of COB matrices can reach 170 Lm/W.

COB Benefits

The main advantages of MCOB technology are:

1. High light output (more than 100 lm/W);
2. The ability to achieve a high intensity of the luminous flux with a relatively small size;
3. Compatible with various drivers, incl. with dimming;
4. Uniformity of the light flux, no shadow effect;
5. Compactness, small size, availability of various shapes;
6. The possibility of manufacturing matrices of any color temperature from 2700K to 7000K;
7. Color rendering index up to 90Ra;

Disadvantages of COB

The main disadvantage of COB technology is the obligatory provision of good heat dissipation from a powerful COB matrix, which is difficult to provide, 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 interface surfaces is not cooled enough, starts to overheat and, in the end, burns out.

As a confirmation, we can cite the following fact: not so long ago, we received 57 LED spotlights (COB) with a power of 100W for diagnostics and repair. Judging by their appearance (see photo), from the cheap GS Light series.

After the 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 technology (Surface Mounting Device) - literally can be translated as "surface mount 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 provides smaller design dimensions, better heat dissipation, and variability in execution. This design is by far the most common in lighting and is used in almost all types of light sources.

To date, it is SMD technology that is the most common in LED lighting and is used in almost all types of luminaires.

This technology is directly created to organize powerful diffused lighting, which is achieved by distributing a significant number of small LEDs over the entire area of ​​\u200b\u200bthe lamp (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 body 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 area aluminum ruler, and the distance between them is large enough, LED cooling does not cause much difficulty, hence the durability of SMD rulers when properly powered.

Of the minuses of fixtures with SMD lines, one should note the great complexity of their repair, since if one LED fails, the entire line stops burning, and replacing the SMD LED on your own is a rather time-consuming task. Replacing the entire line is already expensive financially. In fairness, it must be said that most LED lamp manufacturers in Russia, in the event of a warranty case, replace the entire line.

COB and SMD Applications

1. General case

I would make a section like this: if the form factor of the lamp housing allows you to place a sufficiently large cooling radiator, then you can use COB LED lamps, limiting their power to 30 watts. All lighting equipment with higher power is exclusively SMD. In general, it will become an ideal option for introducing LED lighting.

2. Passed 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. Their work time should be enough for you to hide from the field of view ... :)

3. Short run 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 fearlessly choose COB. The matrix simply will not have time to overheat.

4. Organization of temporary lighting.

For the organization of temporary lighting (for example, on a construction site when performing finishing work), I would recommend using COB spotlights with a power of 20 - 30 W.

5. Lighting of warehouses, industrial premises

In warehouses, industrial buildings and premises, powerful lamps are usually used, suspended at a high (6-12 meters) height. For their electric lighting, it is strongly recommended to use lamps made on SMD LED strips. When choosing fixtures, pay special attention to the presence of well-defined radiators, the purpose of which is to dissipate excess heat into the environment.