We independently repair the LED backlight in an LG TV. DIY LED lighting

LED backlighting is another characteristic of TVs and monitors, which has recently complicated the buyer’s choice, requiring him to think twice and make a responsible decision... The fact is that there are more and more LCD TVs, and their types are increasing time multiply.

Indeed, when purchasing a TV, you want not to make a mistake, not to buy something that represents yesterday or the day before yesterday, which you will soon no longer be able to use...

Fortunately, there are no big difficulties in this issue; its importance is greatly exaggerated - more on this below on the page...

Eat good rule: When buying a TV, it is recommended to pay less attention to the names of the technologies used, and be more guided by your impressions of its appearance and image quality.

At the same time, of course, a more modern (and expensive) TV will in most cases be of better quality.

The best results in image quality today, perhaps, are provided by the type of backlight - Direct (Full) LED. Moreover, it is being improved all the time - now this technology can be used very large number LEDs, which, naturally, has a very positive effect.

Edge LED or its derivatives also show more and more best characteristics, also allowing you to make TVs very thin.

In both cases in best models TVs also use the “Local Dimming” method - Local Dimming. In LG TVs, the backlight using it is called LED plus.

The LCD elements that make up LCD TV panels will not produce images on their own unless they are backlit. Therefore, one or another type of illumination in modern TVs definitely present. It should be borne in mind that technologies are constantly improving, and the type of illumination with the same or similar name next year may be very different in execution from last year. For example, Full screens LEDs now come in nearly as thin as Edge LEDs.

Among the types of TV backlights used or used by SONY are the following:

CCFL (Cold Cathode Fluorescent Lamp).

WCG-CCFL (Wide Range Backlight) color range cold cathode fluorescent lamps).

RGB LED, or dynamic rgb led (Provides color illumination of individual parts of the monitor or TV screen. Potentially a very promising technology, since in theory it makes it possible to illuminate the desired area of ​​the screen a certain color. In practice, its theoretical advantages over other types cannot always be realized. See details below on the page).

Full LED. Another name is Direct LED (backlit diodes are located behind the screen evenly over its entire area. This simplifies control and improves quality. But it negatively affects the thickness of the screen.) - Edge LED (The liquid crystal screen is illuminated by white LEDs installed at the top and bottom or on the sides . Allows the production of very thin Slim TVs).

Dynamic Edge LED (In addition, Local Dimming technology is used, which controls the amount of illumination of individual groups of LEDs depending on the displayed image).

Intelligent Dynamic LED. Another name is Full LED or Direct LED (Compared to previous technologies, many more white illuminating LEDs are used, located directly behind the TV screen evenly across its entire area and illuminating the image. By controlling the glow of individual blocks of LEDs, the system can illuminate specific areas of the image, leaving others dark. This technology simplifies operation and improves quality, but has a negative impact on screen thickness.)

Other TV manufacturers, Samsung, Sharp, LG or Toshiba use different technologies to varying degrees. Accordingly, the TV backlight options may also have a different name (you can get a lot of information about technologies on the Internet, but from the point of view of choosing an option for purchase, this information will not give much. It is more important, as we have already said, to evaluate the TV picture visually).

By the way, Full LED (Intelligent Dynamic LED) from Sony is not the same as full LED backlighting in the original sense at the beginning of technology development, when the fluorescent lamp backlight of the LCD matrix of TVs was simply replaced by thousands of individual light-emitting diodes (LEDs).

Compared to previously used technologies, LED LCD backlight(LCD) TVs have quite a few advantages, but there are also disadvantages (inherent to the technology itself):

Disadvantages of LED technology

Initially, this type of backlight does not improve the viewing angles of the LCD (LCD) display
- Thinner models with edge LED backlighting may suffer from uneven screen illumination
- LED backlighting can lead to local unwanted darkening of the image.

Of course, these shortcomings in most cases are successfully overcome in specific models TVs and monitors, since the technology itself is improving all the time. In addition, not only the backlight affects the quality of the picture on the screen.

Advantages of LED TVs

All LED types backlights are more economical
- Technologies such as Edge LED allow you to create TVs with very thin screens
- LEDs does not contain mercury (although their manufacturing technology uses gallium and arsenic)

Of course, miracles do not happen. As a rule, a more expensive model will have a higher quality image and is considered the most promising at the moment time type of screen backlight. But the image will be good not only and not necessarily because of the backlight. All other TV devices, including the video processor, can be very good quality. The TV can be very well tuned (what used to be called "calibrated"). In the end, the adjustments can be made correctly and appropriately for the given lighting...

From all this, in our opinion, we can conclude:

When choosing a TV, you should not pay much attention to the type of backlight. It will be better if you personally compare the image quality of several models and choose the one whose picture seems nicer.

And choosing which type of backlight is better is the task of manufacturers. While they themselves cannot come to an established opinion (which is natural, because technology is moving forward very quickly).

Take for example RGB LED backlight It is believed to provide a much richer color gamut, extremely sharp and contrasting images on the screen, but it has not become widespread over time. On the contrary, it seems that manufacturers are abandoning it. Firstly, it is much more expensive than other types. It also has technical limitations: the number of backlight elements is limited, since controlling every part of the monitor is too difficult and expensive. As a result, some of the scene illumination that should be bright may be reduced.

Addition:

Lately There is information about successful improvements to this technology by Mitsubishi. Moreover, they are developing completely new type RGB Backlit lighting using a three-color laser. Perhaps soon they will start talking about RGB lighting again in full voice.

Sergey Filinov

LED backlighting in modern TVs with liquid crystal screens today has several technological solutions. In an effort to increase the color gamut to better display colors, TV display manufacturers have developed new backlighting methods that differ from conventional LEDs.

RGB LED

To obtain a wide spectrum of white light, they began to use triads of LEDs consisting of blue, green and red colors in the backlight.

It was an alternative to WLED with a white LED and a smaller color gamut. The lighting system with three different LEDs is called RGB LED. The color gamut of screens with RGB backlighting was greater than those using only white LEDs or using fluorescent CCFL lamps. But there were also disadvantages: price, size, weight, different times aging of LEDs of different colors, which over time led to image color mismatch. Therefore, we abandoned RGB LED backlighting in favor of WLED.

RGB LED

WLED

Given the shortcomings of RGB backlighting, TV manufacturers have settled on using “white” LEDs. They are located either on the sides of the case or in one array behind the LCD matrix. With the help of special diffusers, the light from the diodes is evenly distributed across the entire screen.

Although we call these LEDs “white,” they actually emit blue light, which passes through a yellow filter and is converted to white. Therefore, the use of white LEDs in screens back in 2010 gave a bluish tint to the image.

Over time, manufacturers have improved the components, and the WLED backlight has become quite functional, but as far as the light spectrum is concerned, some imbalances in the display of colors are noticeable.

This peak in blue is due to the blue LED. Using a filter you can get white light. And this filtered light hits the red, blue and green subpixels to form the entire spectrum of the limited color gamut. Passing through filters, part of the spectrum is lost, and the flux intensity at the frequency corresponding to blue will be greater than at red and green. Using screen calibration you can get correct colors, but these reasons allow the WLED-backlit screen to display colors in only sRGB space.

If a display with WLED displays colors in the picture close to blue (shades of blue), then the advantage in the spectrum is precisely blue may put pressure on other colors that will be mixed to create the shade. Therefore, shades close to blue may not be displayed correctly.

There was a similar problem when using a CCFL lamp, but there the problem was with the green color. It was in green that the peak intensity was visible.

Increased color gamut

To expand the color gamut beyond sRGB and move to the next color standard, changes were made to the WLED backlight.

And after the changes they began to use the name GB-R LED or GB-r LED. Now, instead of a white LED, a combined blue and green LED coated with a red phosphor is used.

This technology allows you to get peaks in the spectrum in red, green and blue.

This technology is used today in LG on AH-IPS matrices and in Samsung on PLS. Using GB-r LED technology, you can achieve 99% Adobe RGB coverage.

Some manufacturers use a different method to increase the color gamut in their screens. They take a mixture of blue and red LEDs and use a green phosphor for the filter. This technology is called RB-LED or RB-G LED.

Time passes unnoticed and seemingly recently purchased equipment is already breaking down. So, having worked their 10,000 hours, the lamps of my monitor (AOC 2216Sa) gave up their life. At first, the backlight did not turn on the first time (after turning on the monitor, the backlight turned off after a few seconds), which was solved by turning the monitor on/off again; over time, the monitor had to be turned off/off 3 times, then 5, then 10, and at some point it could not turn on the backlight, regardless of the number of attempts to turn it on. The lamps brought to the light of day turned out to have blackened edges and were legally thrown into scrap. An attempt to supply replacement lamps (new lamps were purchased suitable size) was not successful (the monitor was able to turn on the backlight several times, but quickly went into on-off mode again) and finding out the reasons for what the problem could be in the electronics of the monitor led me to the idea that it would be easier to assemble your own monitor backlight using LEDs than repair the existing inverter circuit for CCFL lamps, especially since there have already been articles on the Internet showing the fundamental possibility of such a replacement.

Disassembling the monitor

LED strip lighting

Vout = Vref * (R1+R2)/R1

Where Vref = 1.275V, R1 in the formula corresponds to R1 in the diagram, and R2 in the formula corresponds to a pair of resistors RV1+RV2 in the diagram (two resistors have been introduced for smoother brightness adjustment and reducing the range of voltages regulated by the variable resistor RV1).
I took 1kOhm as R1, and the selection of R2 is carried out according to the formula:

R2=R1*(Vout/Vref-1)

The maximum voltage we need for the tape is 13V (I took a little more than the nominal 12V so as not to lose brightness, and the tape will survive such a slight overvoltage). Those. maximum value R2 = 1000*(13/1.275-1) = 9.91 kOhm. The minimum voltage at which the tape still glows at least somehow is about 7 volts, i.e. minimum value R2 = 1000*(7/1.275-1) = 4.49 kOhm. Our R2 consists of a variable resistor RV1 and a multi-turn trimmer resistor RV2. The resistance of RV1 is 9.91 kOhm - 4.49 kOhm = 5.42 kOhm (we select the closest value of RV1 - 5.1 kOhm), and RV2 is set to approximately 9.91-5.1 = 4.81 kOhm (in fact, it is best to first assemble the circuit, set the maximum resistance of RV1 and measure the voltage at at the LM2941 output, set the resistance RV2 so that the output has the desired maximum voltage(in our case about 13V).

Installation of LED strip

Pd = (Vin-Vout)*Iout +Vin*Ignd

For my case, it is Pd = (13.6-13)*0.7 +13.6*0.006 = 0.5 Watt, so it was decided to make do with the smallest radiator for the LM2941 (placed through a dielectric pad since it is not isolated from the ground in the LM2941).
The final assembly showed that the design was fully functional:


Among the advantages:

• Uses standard LED strip
• Simple control board

• Insufficient backlight brightness in bright conditions daylight(the monitor is in front of the window)
• The LEDs in the strip are not spaced closely enough, so small cones of light from each individual LED are visible near the top and bottom edges of the monitor
• The white balance is a little off and goes slightly greenish (most likely this can be solved by adjusting the white balance of either the monitor itself or the video card)

Adjusting brightness using PWM

More dense LED backlight

• Quite high brightness (possibly comparable, and perhaps even superior to the brightness of the old CCTL backlight)
• The absence of light cones at the edges of the monitor from individual LEDs (LEDs are located quite often and the backlight is uniform)
• Still a simple and cheap control board

• The issue with the white balance, which goes into greenish tones, has not been resolved
• LM2941, although with a large heatsink, gets hot and heats everything inside the case

Control board based on step-down regulator

Vout=Vref*(1+R2/R1)

Where Vref = 1.23V. For a given R1, you can obtain R2 using the formula:

R2=R1*(Vout/Vref-1)

In calculations, R1 is equivalent to R4 in the circuit, and R2 is equivalent to RV1+RV2 in the circuit. In our case, to adjust the voltage in the range from 7.25V to 10.5V, we take R4 = 1.8 kOhm, variable resistor RV1 = 4.7 kOhm and trimming resistor RV2 at 10 kOhm with an initial approximation of 8.8 kOhm (after assembling the circuit, it is best to set its exact value by measuring the voltage at the output of LM2576 at maximum resistance RV1).
I decided to make a board for this regulator (the dimensions did not matter, since there is enough space in the monitor to mount even a large board):


Control board assembly:


After installation in the monitor:


All assembled:


After assembly everything seems to work:


Final option:


Advantages:

• Sufficient brightness
• Step-down regulator does not heat up and does not warm up the monitor
• There is no PWM, which means nothing blinks at any frequency
• Analogue (manual) brightness control
• No restrictions on minimum brightness (for those who like to work at night)

• The white balance is slightly shifted towards green tones (but not much)
• At low brightness (very low), unevenness in the glow of LEDs of different assemblies is visible due to the spread of parameters

Improvement options:

• White balance is adjustable both in the monitor settings and in the settings of almost any video card
• You can try installing other LEDs that will not noticeably disrupt the white balance
• To eliminate the uneven glow of LEDs at low brightness, you can use: a) PWM (adjust the brightness using PWM by always applying the rated voltage) or b) connect all the LEDs in series and power them regulated source current (if you connect all 180 LEDs in series, you will need 630V and 20mA), then the same current must pass through all the LEDs, and each will have its own voltage drop, the brightness is regulated by changing the current and not the voltage.
• If you want to make a PWM-based circuit for LM2576, you can use a NAND circuit at the On/Off input of this Step-down regulator (similar to the above circuit for LM2941), but it is better to put a dimmer in the gap of the negative wire of the LEDs via a logic-level mosfet

Every person, when choosing a TV for themselves, learns about the latest achievements of science, gets acquainted with new technologies and terms. One of modern technologies in the field of television is LED. In reality, an LED TV is an ordinary liquid crystal LCD TV. This means that the image in it is formed using a matrix consisting of pixels.

If in older devices the backlight was a fluorescent lamp, then in LED models the backlight is a matrix consisting of a set of LEDs (Light Emitting Diode).

Light Emitting Diode is translated as “light emitting diode”. The scope of their application is extensive: these are car headlights, traffic lights, lamps, spotlights, street and home lamps. In a TV, light from LEDs is directed onto the LCD screen, illuminating the image.

Of course, it would be more logical to call these models LCD TVs with LED backlighting. However, Samsung, which is a pioneer in this field, called these models "LED TV". The term became popular and began to denote a class of new televisions. The LEDs in these TV receivers do not form a picture as a real unit (pixel). Therefore, LED TVs cannot be considered full-fledged LED models.

How LED lighting works

To understand the operating principles and features of this device, you need to become familiar with the types of backlighting on a TV. Currently, several lighting systems have been developed. They differ from each other in their location and color.

Color of glow sources

Single color system (White led) more energy efficient than fluorescent lamps, but is still considered a budget option. LEDs do not contain mercury, like lamps, but in terms of color rendering and coverage depth, LED TVs with this backlight are practically no different from LCDs.

Multi-color system (RGB) compares favorably with the previous version. TVs with this backlight have a wide color palette. Accordingly, very good color rendition. Unfortunately, this effect comes at a higher price. To operate such models you need a modern, powerful GPU. These TVs consume more electricity and have a more bulky, comparatively, of course, body. The cost of these TVs limits demand, so leading companies are gradually abandoning RGB backlighting and are looking towards analog household appliances.

Mixed backlight option (QD VIsion) uses only blue LEDs and special films. The film is a collection of quantum dots that have red and green colors. This allows you to have a tuned spectrum of optical waves, limited in range. Due to this, the color palette expands, and the brightness and intensity improves. Unlike the RGB system, this technology is more energy efficient.

The answer to the question of which backlight option to use is ambiguous. There are still various controversial opinions and discussions on this matter. Toshiba believes that white backlighting, based on all its characteristics, is preferable to RGB.

Accommodation options

There are two options for placing the backlight:

General advantages of LED TVs

These devices are an undoubted step forward in the development of television. They enjoy deserved popularity in everyday life. There are several main advantages:

Manufacturers are constantly working to improve these panels. The new technology is called OLED TV. In these TVs, the backlight is organized using organic light-emitting diodes. They are even more characteristic slim body and improved color rendering.

Speaking about LED technologies, we should not forget that in the manufacture of LED TVs they do not use, as before, harmful substances - mercury and aerosols.

Some LED-TV models use “local dimming” technology. It is designed for local dimming. The basic idea is to control groups of LEDs. Each group contains several elements. True, with such an approach separate areas bright spots sometimes appear on the screen in areas where the backlight is turned on full power. And where the backlight is not used, dark spots may appear.

Screen resolution. Determined by the number of pixels that form the image in width and height. The larger this parameter, the more clear image and more different details can be seen on the screen.

LED-TVs mainly have Full HD (1980×1920 pixels) and H.D. Ready (1366×768 pixels) resolution. These are the most popular video formats in present moment. Some premium models have 4K UHD resolution (3840x2160 pixels).

Almost all 4K UHD TVs support HDR. This is an extended format dynamic range, which allows you to depict a picture as close to reality as possible.

Screen coating. There are matte and glossy. At matte finish the image is softer. The viewing angle is limited. When hit sunlight no glare. If the coating is glossy, then the picture on the screen is very bright and contrasting. In bright sunlight, visibility becomes worse.

Functional connectors. Usually there are standard ones: HDMI output, Ethernet output and USB connector for watching video from a flash drive or hard drive. IN latest models there is a D-sub video port. It involves connecting a computer to a TV.

Sweep frequency. An indicator of how many frames of a film are shown per second. It is measured in Hertz and can reach values ​​up to 960 Hz. For 3D TVs, the frequency can be even higher. The recommended range of values ​​so that the image does not blur and pictures do not overlap one another is 100−200 Hz.

Additional features

DVB-T. Standard digital television. Allows, in addition to analog cable and terrestrial television, connect satellite.

Volumetric 3D image. Using this option, you can view 3D images with active or passive 3D. It is necessary to take care of special glasses.

Smart TV. Allows you to connect and use the Internet. Connection occurs via WiFi module. Connection possible via network cable. Some TVs allow you to build in an additional router. With Smart T.V. you can play videos from the Internet, play, listen to music, and search for information.

LED devices have become popular. After all, LED TV - what does it mean? This high quality, convenience and comfort of use. The advantage of an LCD TV is LED backlighting; all LED models have it. But for the design features, additional features sometimes you have to pay extra. What should you pay attention to when choosing an LED TV model?

First of all, you need to decide which diagonal is best to choose. The stores offer a huge selection different models from 19 to 58 inches. Sometimes it’s not very common to calculate in inches and you have to select the size in centimeters, that is, from 48 to 147 cm. The right choice diagonal depends on the size of the room where the TV will be installed.

There is an approximate table of the ratio of diagonal and distance to comfortable viewing.

These data are approximate and allow adjustments within half a meter.

• 14−17 inches - from 1.5 to 2 m.
• 21−25 inches - from 2 to 3 m.
• 26−32 inches - from 3 to 4 m.
• 34−37 inches - from 4 to 5 m.
• 42−55 inches - from 5 to 7 m.
• 61−80 inches - from 7 to 10 m.

So, when choosing a TV, you need to think about its location in the room in advance and select optimal model, based on the layout.

After choosing the TV diagonal, you need to consider the resolution. Here the criterion is the larger the better. Full HD will provide complete comfort and satisfaction from your TV.

The quality of the picture is assessed subjectively. If possible, colors should be natural, without overexposed areas or spots. The image during fast movement should not be jerky, but smooth. The black color must be free of impurities, as black as possible. You should check the transmission of halftones to see if the details are different. The color of the human body: hands, face should be pleasant, without yellow or red spots.

Manufacturers need to be well-known. In addition to the guarantee, this also includes service, as well as the availability of various additional parts and accessories in stores and service centers.

And of course you need to think about additional functions. Do you need Internet access or how important is it to connect your laptop to a large screen?

What is the difference between an LCD and an LED TV?

LED technologies are gradually replacing liquid crystal technologies, since the former are more efficient and economical. This is a serious energy saving and best picture on the screen. Although the differences between these LCD and LED approaches lie only in the way the screen itself is illuminated.

Everything is moving forward. Modern films are produced for latest technologies. Therefore, in order to fully immerse yourself in the atmosphere of the new film, it is better to watch it on LED-TV.

Today, devices with LED backlighting - best solution in terms of image quality and equipment cost. Modern solutions in TVs of this type they allow them to compete with expensive plasmas (PDP), confidently displacing the latter from the market.

True OLED TVs are very promising. In these panels, LEDs are truly the imaging unit. But these models are still expensive and pay for themselves only with very large sizes screen.

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