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Do you need LED backlighting on your TV? The backlight in this case will work when the device is connected to the network. We independently create a power supply circuit and adjust the brightness of the backlight

Time passes imperceptibly and it would seem that recently purchased equipment is already out of order. So, having worked out their 10,000 hours, the lamps of my monitor (AOC 2216Sa) ordered to live for a long time. 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 already 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 taken out into the light of God turned out to be with blackened edges and legally went to the scrap. An attempt to put replacement lamps (new lamps of a suitable size were bought) was unsuccessful (the monitor was able to turn on the backlight several times, but quickly went back to on-off mode) and finding out the reasons for what could be the problem already in the monitor electronics led me to the idea about the fact that it will be easier to assemble your own monitor backlight on LEDs than to repair the existing inverter circuit for CCFL lamps, especially since there have already been articles on the network showing the fundamental possibility of such a replacement.

We disassemble the monitor

A lot of articles have already been written on the topic of disassembling the monitor, all monitors are very similar to each other, so in short:
1. We unscrew the mount of the monitor supply and the only bolt at the bottom that holds the back wall of the case



2. At the bottom of the case there are two grooves between the front and back of the case, into one of which we put a flat screwdriver and begin to remove the cover from the latches around the entire perimeter of the monitor (simply by gently turning the screwdriver around its axis and lifting the case cover). It is not necessary to apply excessive efforts, but it is difficult to remove the case from the latches only for the first time (during the repair I opened it many times, so the latches began to be removed much easier over time).
3. We have a view of the installation of the internal metal frame in front of the case:



We take out the board with buttons from the latches, take out (in my case) the speaker connector and, having unbent the two latches at the bottom, we take out the inner metal case.
4. On the left you can see 4 wires for connecting backlights. We take them out by slightly squeezing, because. to prevent falling out, the connector is made in the form of a small clothespin. We also take out a wide cable going to the matrix (at the top of the monitor), squeezing its connector on the sides (because there are side latches in the connector, although this is not obvious at first glance at the connector):



5. Now you need to disassemble the "sandwich" containing the matrix itself and the backlight:



Along the perimeter there are latches that open with a slight prying with the same flat screwdriver. First, the metal frame holding the matrix is ​​​​removed, after which you can unscrew three small bolts (a regular cross-head screwdriver will not work because of their miniature size, you will need an especially small one) that hold the matrix control board and the matrix can be removed (it is best to put the monitor on a hard surface, such as a table covered with fabric matrix down, unscrewing the control board, put it on the table, unfolding it through the end of the monitor and just lift the backlit case by lifting it vertically, and the matrix will remain lying on the table. in order - i.e. cover the matrix lying on the table with the assembled backlit case, wrap the cable through the end to the control board and screwing the control board carefully lift the assembled unit).
It turns out the matrix separately:



And the backlit block separately:



The backlit block is disassembled in a similar way, only instead of a metal frame, the backlight is held by a plastic frame, which simultaneously positions the plexiglass used to diffuse the light from the backlight. Most of the latches are on the sides and are similar to those that held the metal frame of the matrix (open by prying with a flat screwdriver), but on the sides there are several latches that open “inward” (you need to press on them with a screwdriver so that the latches go inside the case).
At first, I memorized the position of all the parts to be removed, but then it turned out that it would not be possible to assemble them “incorrectly”, and even if the parts look absolutely symmetrical, the distances between the latches on different sides of the metal frame and the fixing protrusions on the sides of the plastic frame holding the backlight will not allow them to be assembled “incorrectly” ".
That's actually all - we dismantled the monitor.

LED strip lighting

At first, it was decided to make the backlight from led strip with white LEDs 3528 - 120 LEDs per meter. The first thing that turned out was that the width of the tape was 9 mm, and the width of the backlights (and the seat for the tape) was 7 mm (in fact, there are backlights of two standards - 9 mm and 7 mm, but in my case they were 7 mm). Therefore, after examining the tape, it was decided to cut 1 mm from each edge of the tape, because. this did not touch the conductive tracks on the front of the tape (and on the back, along the entire tape, there are two wide power wires, which will not lose their properties due to a decrease in their properties by 1 mm at a backlight length of 475 mm, because the current will be small). No sooner said than done:



In the same way, the LED strip is carefully cut along its entire length (the photo shows an example of what happened before and what happened after cutting).
We will need two strips of 475 mm tape (19 segments of 3 LEDs per strip).
I wanted the monitor backlight to work in the same way as the regular one (i.e. turned on and off by the monitor controller), but I wanted to adjust the brightness “manually”, like on old CRT monitors, because this is a frequently used function and I got tired of climbing the on-screen menu every time I pressed a few keys (in my monitor, the right-left keys do not adjust the monitor modes, but the volume of the built-in speakers, so the modes each time had to be changed through the menu). For this, a manual was found on the network for my monitor (who will come in handy - attached at the end of the article) and + 12V, On, Dim and GND were found on the page with the Power Board according to the scheme, which we are interested in.



On - signal from the control board to turn on the backlight (+ 5V)
Dim - PWM backlight brightness control
+ 12V turned out to be far from 12, but somewhere around 16V without backlight load and somewhere around 13.67V with under load
It was also decided not to do any PWM backlight brightness adjustments, but to power the backlight direct current(At the same time, the issue is being resolved with the fact that for some PWM backlight monitors it works at a not very high frequency, and for some, the eyes get a little more tired from this). In my monitor, the frequency of the "native" PWM was 240 Hz.
Further on the board, contacts were found to which the On signal is applied (marked red) and + 12V to the inverter unit (the jumper that needs to be unsoldered to de-energize the inverter unit is marked green). (photo can be enlarged to see notes):



The LM2941 linear regulator was taken as the basis of the control circuit, mainly because at a current of up to 1A it had a separate On / Off control pin, which was supposed to be used to control the backlight on / off with the On signal from the monitor control board. True, in the LM2941 this signal is inverted (i.e. there is voltage at the output when the On / Off input is zero potential), so I had to assemble an inverter on one transistor to match the direct On signal from the control board and the inverted input LM2941. The scheme does not contain any other excesses:



The calculation of the output voltage for the LM2941 is made by the formula:

Vout = Vref * (R1+R2)/R1

Where Vref = 1.275V, R1 in the formula corresponds to R1 in the circuit, and R2 in the formula corresponds to a pair of resistors RV1 + RV2 in the circuit (two resistors are introduced for smoother brightness control and reducing the range of voltages regulated by the variable resistor RV1).
As R1, I took 1 kOhm, 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 couple more than the nominal 12V so as not to lose brightness, and the tape will survive such a slight overvoltage). Those. maximum value R2 \u003d 1000 * (13 / 1.275-1) \u003d 9.91 kOhm. The minimum voltage at which the tape still somehow glows is about 7 volts, i.e. minimum value R2 = 1000*(7/1.275-1) = 4.49kΩ. Our R2 consists of a variable resistor RV1 and a multi-turn trimmer RV2. We get the resistance RV1 9.91kOhm - 4.49kOhm = 5.42kOhm (we choose the nearest value of RV1 - 5.1kOhm), and set RV2 at about 9.91-5.1 = 4.81kOhm (in fact, it is best to first assemble the circuit, set the maximum resistance of RV1 and measure the voltage across output LM2941 set the resistance RV2 so that the output has the desired maximum voltage (in our case, about 13V).

Installation of LED strip

Since after cutting the tape by 1 mm, the power wires were exposed at the ends of the tape, I glued electrical tape on the case in the place where the tape will be glued (unfortunately not blue but black). A tape is glued on top (it’s good to warm the surface with a hairdryer, because adhesive tape sticks much better to a warm surface):



Next, the back film, plexiglass and light filters that lay on top of the plexiglass are mounted. Along the edges, I propped up the tape with pieces of eraser (so that the edges on the tape do not come off):



After that, the backlight unit is assembled in the reverse order, the matrix is ​​​​installed, the backlight wires are brought out.
The circuit was assembled on a breadboard (because of simplicity, I decided not to breed the board), it was bolted through the holes in the back wall of the metal case of the monitor:






Power and control signal On were started from the power supply board:



The estimated power allocated to the LM2941 is calculated by the formula:

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

For my case, it is Pd = (13.6-13) * 0.7 + 13.6 * 0.006 = 0.5 Watts, so it was decided to get by with the smallest radiator for the LM2941 (planted through a dielectric gasket because it is not isolated from the ground in the LM2941).
The final assembly showed quite a performance of the design:



Of the advantages:

  • Uses standard LED strip
  • Simple control board
Of the shortcomings:
  • Insufficient backlight brightness in bright daylight (monitor in front of a window)
  • The LEDs in the strip are not spaced often enough to show small cones of light from each individual LED near the top and bottom edges of the monitor
  • The white balance is a little off and goes slightly greenish (most likely it is solved by adjusting the white balance of either the monitor itself or the video card)
Pretty good, simple and a budget option backlight repair. It is quite comfortable to watch movies or use the monitor as a kitchen TV, but probably not suitable for everyday work.

Brightness control with PWM

For those hackers who, unlike me, do not remember with nostalgia the analog brightness and contrast controls on old CRT monitors, you can make control from the standard PWM generated by the monitor control board without removing any additional controls to the outside (without drilling the monitor case). To do this, it is enough to assemble an AND-NOT circuit on two transistors at the input of the On / Off controller and remove the brightness control at the output (set the output voltage to a constant 12-13V). Modified schema:



The resistance of the trimmer resistor RV2 for a voltage of 13V should be around 9.9kOhm (but it is better to set it exactly when the regulator is on)

More dense LED backlight

To solve the problem of insufficient brightness (and at the same time uniformity) of the backlight, it was decided to install more LEDs and more often. Since it turned out that buying LEDs individually is more expensive than buying 1.5 meters of tape and soldering them from there, a more economical option was chosen (soldering LEDs from a tape).
The 3528 LEDs themselves were placed on 4 strips 6 mm wide and 238 mm long, 3 LEDs in series in 15 parallel assemblies on each of the 4 strips (the wiring for the LEDs is attached). After soldering the LEDs and wires, the following is obtained:






The strips are laid two at the top and bottom with wires to the edge of the monitor in a joint in the center:






The nominal voltage across the LEDs is 3.5V (range 3.2 to 3.8V), so an assembly of 3 LEDs in series should be powered by about 10.5V. So the controller parameters need to be recalculated:



The maximum voltage we need for the tape is 10.5V. Those. maximum value R2 = 1000*(10.5/1.275-1) = 7.23kΩ. The minimum voltage at which the assembly of LEDs still somehow glows is about 4.5 volts, i.e. minimum value R2 = 1000*(4.5/1.275-1) = 2.53kΩ. Our R2 consists of a variable resistor RV1 and a multi-turn trimmer RV2. We get the resistance RV1 7.23kOhm - 2.53kOhm = 4.7kOhm, and set RV2 at about 7.23-4.7 = 2.53kOhm and adjust it in the assembled circuit to get 10.5V at the output of LM2941 at maximum resistance RV1.
One and a half times more LEDs consume 1.2A of current (nominally), so the power dissipation on the LM2941 will be equal to Pd = (13.6-10.5) * 1.2 + 13.6 * 0.006 = 3.8 watts, which already requires a more solid heatsink to remove heat:



We collect, connect, we get much better:



Advantages:
  • Sufficiently high brightness (possibly comparable, and possibly even superior to the brightness of the old CCTL backlight)
  • Lack 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
Disadvantages:
  • The issue with the white balance, leaving in greenish tones, was not resolved in any way
  • LM2941, although with a large heatsink, is heated and heats everything inside the case

Control board based on step-down regulator

To eliminate the heating problem, it was decided to assemble a dimmer based on a Step-down voltage regulator (in my case, LM2576 was chosen with a current of up to 3A). It also has an inverted On / Off control input, so the same inverter on one transistor is present for matching:



Coil L1 affects the efficiency of the converter and should be 100-220 μH for a load current of about 1.2-3A. The output voltage is calculated by the formula:

Vout=Vref*(1+R2/R1)

Where Vref = 1.23V. Given R1, you can get 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 = 1.8kΩ, variable resistor RV1 = 4.7kΩ and a 10kΩ trimmer resistor RV2 with an initial approximation of 8.8kΩ (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).
For this regulator, I decided to make a board (the dimensions did not matter, because there is enough space in the monitor to mount even a large board):



Control board assembly:



After mounting in the monitor:



Everyone is here:



After assembly, everything seems to work:



Final variant:



Advantages:

  • Sufficient brightness
  • Step-down controller does not heat up and does not heat the monitor
  • No PWM, which means nothing blinks at any frequency
  • Analog (manual) brightness control
  • No minimum brightness limit (for those who like to work at night)
Disadvantages:
  • Slightly shifted white balance 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

Upgrade options:

  • White balance is adjustable both in the monitor settings and in the settings of almost any video card
  • You can try to put other LEDs that will not noticeably knock down the white balance
  • To avoid uneven illumination of LEDs at low brightness, you can use: a) PWM (adjust the brightness using PWM always supplying the rated voltage) or b) connect all the LEDs in series and feed them with an adjustable current source (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 the LM2576, you can use the NAND circuit at the On / Off input of this Step-down regulator (similar to the above circuit for the LM2941), but it's better to put a dimmer in the gap of the negative wire of the LEDs through the logic-level mosfet

Led backlighting is another characteristic of TVs and monitors, which has recently been complicating the choice of the buyer, requiring him to take extra thought and make a responsible decision ... The fact is that LCD (LCD) TVs are becoming more and more, and its types are all time multiply.

Indeed, when buying a TV, you want not to make a mistake, not to buy something that represents yesterday or the day before yesterday, which will soon be impossible to use ...

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

There is 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 picture quality.

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

Best Results in terms of image quality today, perhaps, the type of backlighting - Direct (Full) LED. Moreover, it is being improved all the time - now a very large number of LEDs can be used in this technology, which, of course, has a very positive effect.

Edge LED or its derivatives also show more and more better characteristics, also making it possible to make TVs very thin.

In both cases, the best TV models also use the Local Dimming method - local dimming. In LG TVs, backlighting with its use is called LED plus.

The LCD elements that make up LCD TV panels will not, by themselves, produce images unless they are backlit. Therefore, one or another type of highlighting in modern TVs necessarily present. At the same time, it should be borne in mind that technologies are constantly being improved, and the type of highlighting with the same or similar name next year may differ greatly in execution from last year. For example, Full LED screens are now available almost as thin as Edge LED.

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

CCFL (Cold Cathode Fluorescent Lamp).

WCG-CCFL (Cold Cathode Fluorescent Lamp Wide Color Illumination).

RGB LED, or dynamic rgb led (Provides color illumination of individual fragments of the monitor or TV screen. Potentially very promising technology, since in theory it makes it possible to highlight the desired area of ​​the screen with a certain color. In practice, its theoretical advantages over other types are not always possible to translate into life (see below on the page for details).

Full LED. Another name for Direct LED (illuminating 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 manufacture of very thin Slim-TVs).

Dynamic Edge LED (In addition, Local Dimming technology is used, which controls the amount of glow 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 over its entire area and illuminating the image. By controlling the glow of individual LED blocks, the system can illuminate specific areas of the image, leaving others dark. This technology simplifies control and improves quality, but has a negative effect on the thickness of the screen.)

Other TV manufacturers such as Samsung, Sharp, LG or Toshiba use different technologies to varying degrees. Accordingly, TV backlight options may also have a different name (you can learn more 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 the development of technology, when the fluorescent lamp backlighting of the LCD matrix of TVs was simply replaced by thousands of individual light-emitting diodes (LEDs).

Compared to previous technologies, LED LED Backlighting LCD (LCD) TVs has enough advantages, but there are also disadvantages (inherent in 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 side LED backlighting may suffer from uneven screen illumination
- LED backlighting can lead to local undesirable dimming of the image.

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

Benefits of LED TVs

All LED types lights are more economical
- Technologies such as Edge LED allow you to create TVs with a very thin screen
- LED light-emitting diodes do 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 better image, and is considered the most promising on the market. this 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, may be very good quality. The TV can be very well tuned (what used to be called "calibrated"). In the end, the adjustments can be correctly and appropriately set for this 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 with which the picture seems more pleasant.

And to choose 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 said to provide a much richer color gamut, extremely sharp and high contrast images on the screen, but it has not been observed to be ubiquitous over time. On the contrary, it seems that manufacturers are abandoning it. First, it is much more expensive than other types. And it also has technical limitations: the number of backlight elements is limited, since it is too difficult and costly to control each part of the monitor. As a result, the portion of the scene illumination that should be bright may be reduced.

Addition:

Recent times information is received about the successful improvements in this technology by Mitsubishi. Moreover, they are also developing a completely new type of RGB Backlit lighting using a three-color laser. Perhaps soon they will talk about RGB backlighting in full voice again.

Sergey Filinov

Hello!
Sometimes when refurbishing LCD illumination , there are difficulties in acquiring the necessary fluorescent (CCFL ) lamps . In such cases, you can convert the lamp backlight to LED. Such an alteration is not so complicated, and there are no special problems with spare parts.
In this article, I offer you the principle of such a reorganization in the form of some instructions.
Replacement steps LCD illumination to LED:

    Disassemble the monitor or TV. After removing the plastic case, carefully disconnect the wires from the board, remove the metal frame from the LCD module and remove the matrix. With the matrix, you need to be especially careful not to damage the fragile connecting cables. If everything is done correctly, then full access to the electronic board, power inverter and backlight elements will be open.







2. Remove the canisters with lamps from the matrix or the lamps themselves, if they are installed without canisters.


3. Disconnect the old lamps and dispose of them. With elements CCFL You also need to be extremely careful, because they contain mercury.
4. We proceed to the replacement stage. First you need to purchase an LED strip, preferably with a margin so that it is enough to replace all the lamps (measure the length of the lamp and multiply by their number). It should be as narrow as possible and with at least 120 LEDs per meter. To make the backlight more pleasing to the eye, it is better to take LEDs with a white glow.


5. Tape with LEDs must be glued to double-sided tape where the lamps were. Next, wires from old lamps are soldered to the contact leads of the tapes and insulated with hot glue. You can immediately check the performance of this design by connecting the wires to an external power source.




6. Now you need to connect the backlight on the power board of the monitor or TV. To do this, you need to find the jumpers marked with the inscription "12 V" and solder the backlight wires there, respectively, observing the polarity. Assemble the monitor in reverse order and enjoy your invention.




Backlight in this case, it will work when the device is connected to the network.
To control the backlight, and bring it to normal operation, you will have to work harder. The wires leading to the LEDs must be powered in such a way that it is possible to turn on the backlight when the on / off buttons are pressed and adjust its brightness. There are 2 options for this:
1. We independently create a power supply circuit and adjust the brightness of the backlight:
  • On the monitor or TV power supply chip, we are looking for a plastic box (connector) with wires pulled out of it, where each socket is signed on the board.


  • Here we are interested in the output of "DIM". He will be responsible for signaling on / off and adjusting the brightness by changing the duty cycle in the PWM controller. The duty cycle of the pulses changes until the desired brightness level is set, and the limit values ​​​​just correspond to turning on and off.
  • Now we need an N-channel field-effect transistor(field worker) any. Wires from the LED strip with a minus are soldered to its drain (Drain), a common wire from the backlight is also connected to the source (source), and the gate (gate) through a 100-200Ω resistor and any wire is connected to the “DIM” output.


  • We still have wires from the backlight with a plus, we output them to the + 12V power source on the microcircuit and solder them.




  • Now we set the backlight to its rightful place and assemble the monitor in reverse order. Do not forget about caution and accuracy in handling the matrix and filters, so that dust does not get in and the cables are not damaged. Everything can be used.




  1. The second way, more expensive, but convenient, is to buy ready-made LED backlight with own inverter :
  • Again, pay attention to the plastic connector and the DIM (brightness) pin and the on/of pin (better to use the pinout).


  • Using a multimeter, the places on the control unit of the old lamps are determined, from which the signal goes to brightness and on / of.
  • Now soldered to the found places of the wire inverter new LED backlight .


  • Still, it is better to unsolder the jumpers from the inverter power supply of the old lamps so that the backlight is regulated by the new inverter.