lcd panel led backlight voltage brands

Monochrome character, graphic and static displays require different input voltages. All the different LCD voltage symbols can be confusing, but believe it or not, there is a system to the madness.

The voltages VCC, VDD, VSS and VEE are used in describing voltages at various common power supply terminals. The differences between these voltages stem from their origins in the transistor circuits they were originally used for.

This LCD voltage terminology originated from the terminals of each type of transistor and their common connections in logic circuits. In other words, VCC is often applied to BJT (Bipolar Junction Transistor) collectors, VEE to BJT emitters, VDD to FET (Field-Effect Transistor) drains and VSS to FET sources. Most CMOS (Complementary metal–oxide–semiconductor) IC data sheets now use VCC and GND to designate the positive and negative supply pins.

In the Pleistocene era (1960’s or earlier), logic was implemented with bipolar transistors. NPN (Negative-Positive-Negative) were used because they were faster. It made sense to call positive supply voltage VCC where the “C” stands for collector. The negative supply was called VEE where “E” stands for emitter.

When FET transistor logic came around a similar naming convention was used, but now positive supply was VDD where “D” stands for drain. The negative supply was called VSS where “S” stands for source. Now that CMOS is the most common logic this makes no sense. The “C” in CMOS is for “complementary” but the naming convention still persists. In practice today VCC/VDD means positive power supply voltage and VEE/VSS is for negative supply or ground.

The convention of VAB means the voltage potential between VA and VB. The convention of using 3 letters was used to show power supply and ground reference voltages as well. In some cases a processor may have both an analog and digital power supply. In this case VCCA/VCCD and VSSA/VSSD are used. Another reason for the 3 letters is in an NPN circuit with a load resister between the collector and VCC. VC would be the collector voltage. In this case VCC is the positive power supply voltage and would be higher than VC.

Pin three (3) is Vo and is the difference in voltage between VDD and VSS. This LCD voltage is adjusted to provide the sharpest contrast. The adjustment can be accomplished through a fixed resistor or a variable potentiometer. Many products have firmware that monitor the temperature and automatically adjust the contrast voltage.

In a Liquid Crystal Display (LCD), V0 is used to vary the screen brightness or contrast. Contrast, simply put is the ratio of the light areas to the dark areas in a LCD. This is usually done in a production setting with values which are optimized for most users. Temperature can have an undesirable effect on the display brightness and for this reason a varying resister or potentiometer is used to accommodate the desires of the user.

Below is a data sheet of a 16x2 Character LCD module that shows various recommended driving voltages. The LCD voltage can range from MIN (minimum) to TYP (Typical) to Max (maximum).

If the supplied LCD voltage drops too low, the display is ‘under-driven’ and will produce segments that are ‘grey’. The lower the LCD voltage falls below the acceptable threshold, the lower the contrast will be.

If the LCD is over-driven, you may see ghosting. This is where segments that should not be ‘on’ are gray. They are not as dark as the segments that should be on, but they can be seen and may cause confusion for the end user.

There are times when a customer needs to replace a display that has been discontinued or EOL (End-Of -Life) by their previous LCD supplier. The previous LCD’s pin-outs may be different than Focus’ standard, off-the-shelf display. This is not a large problem to overcome.

LED backlights are DC (Direct Current) driven and can be supplied from any one of three locations. The most popular is from pins 15 and 16. The second most popular option is to draw power from the ‘A’ and ‘K’ connections on the right side of the PCB.

The third option is to pull power from pins one and two. This is the same location from which the LCD is pulling its power. Focus does not recommend this option and can modify the PCB for the customer to connect the backlight from a different location.

Many LCD Modules will require more than one internal voltage/current. This may make it necessary for the customer to supply the needed inputs. They may need to supply 3V, 5V, 9V, -12V etc.

The solution for this is to integrate a charge pump (or booster circuit) into the LCD circuitry. This solution works in most applications, but if the product will be operating in an intrinsic environment, care must be taken with layout of the circuit board.

Intrinsically-safe LCDs are Liquid Crystal Displays that are designed to operate in conditions where an arc or spark can cause an explosion. In these cases, charge pumps cannot be employed. In fact, the total capacitive value of the display needs to be kept to a minimum.

Focus Display Solutions does not build a display that is labeled ‘Intrinsically safe’ but we do design the LCD to meet the requirements of the engineer. In meeting the design engineer’s requirements, the display may need to contain two or three independent inputs. Focus can redesign the PCB and lay out the traces to allow for these additional inputs.

Custom LCD panels offer several advantages for Original Equipment Manufacturers (OEM). These advantages include the ability for engineering to choose: driving voltage of the LCD, operating temperature of the module, and the configuration of the LED back-light.

The Lighting Emitting Diode (LED) used in LCD back-lights can be manufactured in one of two different configurations: Series or Parallel. There are advantages and disadvantage to both options, so let’s review them both.

The backlight attached to a custom LCD panel may contain LEDs wired in series. Take for example that four LEDs are connected in series. Each LED will have the same current (amps) passes through each of them, in other words the current that passes through LED #1 is the same current that passes through LED #2 etc. So if a battery, which is connected in series with your LEDs, provides 3 amps, then the current though each LED will be the same 3 amps.

Voltage behavior for a series circuit used in your custom LCD panel is just the opposite of current. Each LED removes, or decreases, the voltage as it passes through the LED. This is called a ‘voltage drop’ since the voltage decreases, or drops, as it passes through the LED.

A ‘voltage drop’ means that the voltage level goes down for each LED. So if your battery supplies 12 volts and you have 4 LED’s. Then each LED will draw or reduce the voltage by 3 volts(12 volts divided between 4 LEDs). If you reduce the LED count from 4 to 2, the voltage drop for each LED will now be 6 volts. (12 volts divided between 2 LEDs)

In parallel, each LED incorporated on your custom LCD panel, produces a current drop. This means if you have a battery that provides 6 amps and your parallel circuit has 6 LEDs. Then each LED will draw or decrease the current by 1 amp. If you reduce the number of LED’s from 6 to 3. Your current for each LED will now be 2 amps (6 amps divided by 3 LEDs equals 2 amps per LED)

The voltage for each LED in parallel is the same for each LED. If you have a battery that supplies 10 volts, then each LED will have 10 volts supplied to it.

If you have a 10 volt battery and 3 LEDs, each LED will have 10 volts supplied to each LED. If you take the same 10 volt battery and connect it to 100 LEDs. Each one of the one-hundred LEDs will have 10 volts supplied to it. Below is a diagram of a three LEDs wired in parallel.

Each option has its advantages and disadvantages for your custom LCD panel. Contact one of our technical customer support people for help with the design.

This is a universal LED kit that includes 2 high brightness LED strips, a DC-DC LED driver, and a wire harness.  The LED strips can be easily trimmed in designated increments every 3 LEDs, to fit any size LCD from 10.4"-19". This is known as a cut-to-fit model. This LED bar can be used for LED replacement or CCFL conversion.

Make sure you have an appropriate power supply before installing.  The driver is expecting analog DC voltage.  The driver is designed to operate 2 LED strips at the same time; operating only 1 LED strip may have higher brightness but will reduce the life of the LED strip (to less than 10,000 hours).  If connecting Single LED Strip directly to analog DC source, the recommended input is 10V-11V DC.

NOTE: Plazmo does not have user manuals because every model of LCD power supply board is different.  The customer must have some technical expertise to identify the power source on the monitor power supply board.

This product is commonly used for replacing backlights in a variety of different LCD panels found in gaming machines, POS, ATM and many other applications.

This is a universal LED kit that includes 2 high brightness LED strips, a DC-DC LED driver, and a wire harness.  The LED strips can be easily trimmed in designated increments every 3 LEDs, to fit any size LCD from 10.4"-24". This is known as a cut-to-fit model. This LED bar can be used for LED replacement or CCFL conversion.

Make sure you have an appropriate power supply before installing.  The driver is expecting analog DC voltage.  The driver is designed to operate 2 LED strips at the same time; operating only 1 LED strip may have higher brightness but will reduce the life of the LED strip (to less than 10,000 hours).  If connecting Single LED Strip directly to analog DC source, the recommended input is 10V-11V DC.

NOTE: Plazmo does not have user manuals because every model of LCD power supply board is different.  The customer must have some technical expertise to identify the power source on the monitor power supply board.

This product is commonly used for replacing backlights in a variety of different LCD panels found in gaming machines, POS, ATM and many other applications.

This article is about backlights in liquid crystal displays. For the rear window of an automobile, see Car glass. For the lighting design practice, see Backlighting (lighting design). For other uses, see Backlight (disambiguation).

A backlight is a form of illumination used in liquid crystal displays (LCDs). As LCDs do not produce light by themselves—unlike, for example, cathode ray tube (CRT), plasma (PDP) or OLED displays—they need illumination (ambient light or a special light source) to produce a visible image. Backlights illuminate the LCD from the side or back of the display panel, unlike frontlights, which are placed in front of the LCD. Backlights are used in small displays to increase readability in low light conditions such as in wristwatches,smart phones, computer displays and LCD televisions to produce light in a manner similar to a CRT display. A review of some early backlighting schemes for LCDs is given in a report Engineering and Technology History by Peter J. Wild.

Simple types of LCDs such as in pocket calculators are built without an internal light source, requiring external light sources to convey the display image to the user. Most LCD screens, however, are built with an internal light source. Such screens consist of several layers. The backlight is usually the first layer from the back. Light valves then vary the amount of light reaching the eye, by blocking its passage in some way. Most use a fixed polarizing filter and a switching one, to block the undesired light.

An ELP gives off uniform light over its entire surface, but other backlights frequently employ a diffuser to provide even lighting from an uneven source.

Backlights come in many colors. Monochrome LCDs typically have yellow, green, blue, or white backlights, while color displays use white backlights that cover most of the color spectrum.

Colored LED backlighting is most commonly used in small, inexpensive LCD panels. White LED backlighting is becoming dominant. ELP backlighting is often used for larger displays or when even backlighting is important; it can also be either colored or white. An ELP must be driven by relatively highAC power, which is provided by an inverter circuit. CCFL backlights are used on larger displays such as computer monitors, and are typically white in color; these also require the use of an inverter and diffuser. Incandescent backlighting was used by early LCD panels to achieve high brightness, but the limited life and excess heat produced by incandescent bulbs were severe limitations. The heat generated by incandescent bulbs typically requires the bulbs to be mounted away from the display to prevent damage.

For several years (until about 2010), the preferred backlight for matrix-addressed large LCD panels such as in monitors and TVs was based on a cold-cathode fluorescent lamp (CCFL) by using two CCFLs at opposite edges of the LCD or by an array of CCFLs behind the LCD (see picture of an array with 18 CCFLs for a 40-inch LCD TV). Due to the disadvantages in comparison with LED illumination (higher voltage and power needed, thicker panel design, no high-speed switching, faster aging), LED backlighting is becoming more popular.

LED backlighting in color screens comes in two varieties: white LED backlights and RGB LED backlights.blue LED with broad spectrum yellow phosphor to result in the emission of white light. However, because the spectral curve peaks at yellow, it is a poor match to the transmission peaks of the red and green color filters of the LCD. This causes the red and green primaries to shift toward yellow, reducing the color gamut of the display.a red, a blue, and a green LED and can be controlled to produce different color temperatures of white. RGB LEDs for backlighting are found in high end color proofing displays such as the HP DreamColor LP2480zx monitor or selected HP EliteBook notebooks, as well as more recent consumer-grade displays such as Dell"s Studio series laptops which have an optional RGB LED display.

RGB LEDs can deliver an enormous color gamut to screens.additive color) the backlight can produce a color spectrum that closely matches the color filters in the LCD pixels themselves. In this way, the filter passband can be narrowed so that each color component lets only a very narrow band of spectrum through the LCD. This improves the efficiency of the display since less light is blocked when white is displayed. Also, the actual red, green, and blue points can be moved farther out so that the display is capable of reproducing more vivid colors.

A newNanosys, claims that the color output of the dots can be tuned precisely by controlling the size of the nanocrystals. Other companies pursuing this method are Nanoco Group PLC (UK), QD Vision, 3M a licensee of Nanosys and Avantama of Switzerland.Sony has adapted Quantum Dot technology from the US company QD Visionedge-lit LED backlight marketed under the term Triluminos in 2013. With a blue LED and optimized nanocrystals for green and red colors in front of it, the resulting combined white light allows for an equivalent or better color gamut than that emitted by a more expensive set of three RGB LEDs. At the Consumer Electronics Show 2015, Samsung Electronics, LG Electronics, the Chinese TCL Corporation and Sony showed QD-enhanced LED-backlighting of LCD TVs.

CCFL backlighting has also improved in this respect. Many LCD models, from cheap TN-displays to color proofing S-IPS or S-PVA panels, have wide gamut CCFLs representing more than 95% of the NTSC color specification.

There are several challenges with LED backlights. Uniformity is hard to achieve, especially as the LEDs age, with each LED aging at a different rate. Also, the use of three separate light sources for red, green, and blue means that the white point of the display can move as the LEDs age at different rates; white LEDs are also affected by this phenomenon, with changes of several hundred kelvins being recorded. White LEDs also suffer from blue shifts at higher temperatures varying from 3141K to 3222K for 10 °C to 80 °C respectively.Benq G2420HDB consumer display has a 49W consumption compared to the 24W of the LED version of the same display (G2420HDBL).

To overcome the aforementioned challenges with RGB and white LED backlights an "advanced remote phosphor" cockpit displays,Air Traffic Control displays and medical displays. This technology uses blue pump LEDs in combination with a sheet on which phosphorous luminescent materials are printed for colour conversion. The principle is similar to Quantum Dots, but the phosphors applied are much more robust than the quantum dot nano-particles for applications that require long lifetime in more demanding operational conditions. Because the phosphor sheet is placed at a distance (remote) of the LED it experiences much less temperature stress than phosphors in white LEDs. As a result, the white point is less dependent on individual LEDs, and degrading of individual LEDs over lifetime, leading to a more homogenous backlight with improved colour consistency and lower lumen depreciation.

The use of LED backlights in notebook computers has been growing. Sony has used LED backlights in some of its higher-end slim VAIO notebooks since 2005, and Fujitsu introduced notebooks with LED backlights in 2006. In 2007, Asus, Dell, and Apple introduced LED backlights into some of their notebook models. As of 2008Lenovo has also announced LED-backlit notebooks. In October 2008, Apple announced that it would be using LED backlights for all of its notebooks and new 24-inch Apple Cinema Display, and one year later it introduced a new LED iMac, meaning all of Apple"s new computer screens are now LED. Almost every laptop with a 16:9 display introduced since September 2009 uses LED-backlit panels. This is also the case for most LCD television sets, which are marketed in some countries under the misleading name LED TV, although the image is still generated by an LCD panel.

Most LED backlights for LCDs are edge-lit, i.e. several LEDs are placed at the edges of a lightguide (Light guide plate, LGP), which distributes the light behind the LC panel. Advantages of this technique are the very thin flat-panel construction and low cost. A more expensive version is called full-array or direct LED and consists of many LEDs placed behind the LC panel (an array of LEDs), such that large panels can be evenly illuminated. This arrangement allows for local dimming to obtain darker black pixels depending on the image displayed.

Using PWM (pulse-width modulation, a technology where the intensity of the LEDs are kept constant, but the brightness adjustment is achieved by varying a time interval of flashing these constant light intensity light sources

For a non-ELP backlight to produce even lighting, which is critical for displays, the light is first passed through a lightguide (Light guide plate, LGP) - a specially designed layer of plastic that diffuses the light through a series of unevenly spaced bumps. The density of bumps increases further away from the light source according to a diffusion equation. The diffused light then travels to either side of the diffuser; the front faces the actual LCD panel, the back has a reflector to guide otherwise wasted light back toward the LCD panel. The reflector is sometimes made of aluminum foil or a simple white-pigmented surface.

The LCD backlight systems are made highly efficient by applying optical films such as prismatic structure to gain the light into the desired viewer directions and reflective polarizing films that recycle the polarized light that was formerly absorbed by the first polarizer of the LCD (invented by Philips researchers Adrianus de Vaan and Paulus Schaareman),

The evolution of energy standards and the increasing public expectations regarding power consumption have made it necessary for backlight systems to manage their power. As for other consumer electronics products (e.g., fridges or light bulbs), energy consumption categories are enforced for television sets.

Illuminating Arrangement for a Field-Effect Liquid-Crystal Display as well as Fabrication and Application of the Illuminating Arrangement, filed Oct. 15, 1976.

LED TVs: 10 things you need to know; David Carnoy, David Katzmaier; CNET.com/news; 3 June 2010; "LED TVs: 10 things you need to know". Archived from the original on 2017-12-01. Retrieved 2017-11-22.

LED local dimming explained; G. Morrison; CNET.com/news; 26 march 2016; "LED local dimming explained". Archived from the original on 2017-11-23. Retrieved 2017-11-20.

Dimming options for LCD brightness; J. Moronski; Electronicproducts.com; 3 Januari 2004; "Dimming options for LCD brightness control". March 2004. Archived from the original on 2017-07-28. Retrieved 2017-11-20.

LCD Television Power Draw Trends from 2003 to 2015; B. Urban and K. Roth; Fraunhofer USA Center for Sustainable Energy Systems; Final Report to the Consumer Technology Association; May 2017; "Archived copy" (PDF). Archived from the original (PDF) on 2017-08-01. Retrieved 2017-11-20.link)

Controlling Power Consumption for Displays With Backlight Dimming; Claire Mantel et al; Journal of Display Technology; Volume: 9, Issue: 12, Dec. 2013; Mantel, Claire; Burini, Nino; Nadernejad, Ehsan; Korhonen, Jari; Forchhammer, Soren; Pedersen, Jesper Meldgaard (2013). "Controlling Power Consumption for Displays with Backlight Dimming". Journal of Display Technology. 9 (12): 933–941. Bibcode:2013JDisT...9..933M. doi:10.1109/JDT.2013.2260131. S2CID 24082090.

Broken LCD, or flickering display, or a dull dark display, we have the solution. We can repair or replace the LCD. Backlight or display card problem we have solution for all.

... , and this means the display must be viewable in daylight. These LCDs are very bright indoors due to the fact that their backlights are dynamic and evenly illuminates the screen.

... transmissive LCDs in display technologies. The LCDs provide bright indoor visibility to the strong and even screen illumination provided by backlights. However, in outside environment, standard transmissive ...

... use Transmissive display and illuminate the screen with backlights, offering a bright and clear display indoors. However, they are unreadable and not meant for outdoor use. The Reflective technology ...

VMD 1001 is a 7-inch TFT LCD monitor with 4 wire resistant touch screen sensor. With the high brightness display and automatically brightness control, it is designed for in-vehicle application. In support ...

VMD 2002 is an 8-inch TFT LCD monitor with 4 wire resistant touch screen sensor. With the high brightness display and automatically brightness control, it is designed for in-vehicle applications. In support ...

... 10 Points) Brightness (CD/㎡)：250/350/450nits(optional)Backlight：LED Viewing Angles (CR =10)：170(H)x160(V)Response Time(Typ.Tr+Tf)：5msSignal Connector：VGA/DVI-D/HDMITouch Controller：USBPower Consumption：DC ...

Rackmount monitor with a 16.2 inch 1920 x 1200 WUXGA LED backlight LCD panel, VGA + DVI-D + HDMI video input, and a 6U high rackmount monitor enclosure. Option for IP65 ...

... WES AU19 is an anti-glare LED open frame monitor that uses very little power through LED backlight technology. Particularly noteworthy is the wide temperature range of ...

Modularize mechanical design provides flexible productBuild-in touch screen for interactive application350 cd/m2 (typ) / 600 : 1LED backlight, Long life, 35,000 hrs (typ)-10 oC ~ 50oC ...

... display and NEMA 4X rating to be resistant to dirt, debris, liquids and corrosives. In addition, the FP15-PMT-HB-1700 has an LED backlight life of 70,000 hours.

Plasma screens contain tiny pockets of gas that get excited when voltage is applied to them, turning them into a state of plasma. In that state, the voltage then strikes electrons of mercury, turning them into ultraviolet (UV) light, which isn"t visible to the human eye. The UV light then passes through phosphor cells; each pixel contains red, green, and blue phosphor cells. Thanks to these phosphor cells, the TV can turn the UV light into colors that are visible on the light spectrum. Essentially, plasma TVs don"t require a light, and each pixel is self-emissive, so how one pixel displays itself is independent of the next pixel.

Since each pixel emits its own light, blacks are really deep. When the television wants to display black, it simply emits no light at all for the selected pixels. However, these aren"t perfect blacks because each pixel retains a bit of voltage, leaving a bit of light to pass through. Each pixel emits light in all directions, creating wide viewing angles, so the image remains accurate when viewing from the side.

OLED TVs have similar characteristics to plasmas with their infinite contrast ratio, wide viewing angles, near-instant response time, and to a lesser extent, the risk of permanent burn-in. Since 2012, they"ve replaced plasma as a competitor to LCD TVs, and to learn more about OLEDs and how they differ from LCD TVs, see here.

An LCD screen is composed of two parts: the actual liquid crystal display and a light source at the back of the screen (called backlight). A light diffuser is placed between the backlight and the LCD screen to make the source of light uniform across the screen.

The LCD panel doesn"t emit light by itself, and this is why it needs a backlight; it only acts as a filter to block the light on a per-pixel basis. The backlight is always on, and the pixels in the display rotate to allow light through, creating the colors needed for the image. If the screen wants to display black, the LCD pixels rotate to try to block the light completely. If it wants to display white, it lets all light through. Since the display is only a filter, the blacks will not be as deep as with a plasma screen because an LCD panel will always let a small portion of light through.

There are different types of LCD panels, each with its unique characteristics. Vertical Alignment (VA) panels generally have a high contrast ratio and narrow viewing angles, while In-Plane Switching (IPS) panels have a low contrast ratio with wide viewing angles. You can read about their differences here.

By using a backlight, LCD TVs use much less power than plasmas, which you can read about here. Also, LCD TVs tend to get much brighter than plasmas, making them more suitable for well-lit rooms. There are two main types of backlights used in LCD screens: CCFL and LEDs.

When someone refers to an LCD TV, they usually mean a Cold-Cathode Fluorescent Lamp (CCFL) backlit LCD screen. The first LCD TVs were lit by CCFLs, but they"re extremely rare as of the start of the 2020s. The backlight is a series of light tubes placed behind the screen. These tubes are very similar to fluorescent lamps used in buildings but smaller.

CCFL-backlit LCD TVs were eventually replaced by LED TVs because they cost less, were made thinner, and required less power. Also, LED TVs have more control over their backlight, resulting in vivid colors and better picture quality.

An LED (Light-Emitting Diode) screen is an LCD screen, but instead of having a normal CCFL backlight, it uses LEDs as the source of light behind the screen. Companies label their TVs as LED, even though they"re technically LCD; it can be confusing at times, but if you see an LED TV, you know it has an LCD panel. These TVs are more energy-efficient and a lot smaller than CCFLs, enabling a thinner television screen.

In a full-array LED screen, the LEDs are distributed evenly behind the entire screen. This produces a more uniform backlight and provides more effective use of local dimming, where it can turn off and dim complete zones of LEDs.

With an edge-lit LED screen, the LEDs are placed at the edges of the screen. Depending on the display, it can be all around the screen, on the left and right sides, or at the top and bottom. This allows the screen to be very thin.

However, it can cause some spots on the screen to be brighter than others, like the edges. This problem is called flashlighting or clouding. It can be seen when watching a dark scene in a dark environment. Also, edge-lit screens usually don"t result in good local dimming as they don"t have control over the dimming zones.

Like the full-array method, the LEDs are directly behind the screen. However, there are very few of them, and they can"t be controlled separately to match the luminosity of the picture.

As TV companies attempt to improve their technology, a new type of LED backlighting has emerged: Mini LED. It uses the same traditional LED backlighting behind an LCD panel, except the LED lights are even smaller. This allows for more lights, creating a brighter image and more control over local dimming. Only a handful of Mini LED TVs were produced before 2021, but it now seems that manufacturers are starting to use the technology more often. The Samsung QN90A QLED is an example of a Mini LED TV.

Another technology, Micro LED, is only in its initial phases of development. This doesn"t even have an LCD panel as each LED pixel is self-emissive, similar to OLEDs, but without the burn-in risk. Currently, there aren"t any Micro LED TVs available at the consumer level; Samsung has produced large Micro LED TVs (over 100 inches), and they"re very expensive. However, we may begin to see Micro LED technology in the consumer TV market soon.

Plasma and LCD each present advantages and disadvantages when it comes to picture quality. Plasma TVs generally offer better contrast, wider viewing angles, and improved response times, while LCD TVs get much brighter and have better reflection handling. LCDs also cost less and can be much thinner, which are two of the main reasons why they took over the market share from plasmas in the mid-2000s. Plasma TVs are now extinct, and although OLEDs share many of the same characteristics, LED-backlight LCD TVs are now the norm, and it"s likely your next TV purchase will have an LCD panel.

Since the 2010’s, cold cathode fluorescent lamps (CCFL) in liquid crystal display (LCD) backlighting have been gradually replaced by light-emitting diodes (LED). This is because LEDs, which contain no mercury, have outperformed in thermal dissipation efficiency, color rendition and cost reduction.

Various LCD TV manufacturers, one after another, have eagerly adopted LED backlighting technology for LCD to achieve the feature of low profile, aiming to increase market share on the arrival of the new home TV generation. The market penetration of LED backlit models has been soaring that most of the LCD TVs are LED backlit on Taiwan’s market today.

LED backlighting technology can be divided into two groups: direct-lit type, and edge-lit type. LEDs, used in direct-lit type backlighting, can be either white or RGB. The differences between these two types and LED power solutions in system perspective will be investigated in this application note. For example, the functional block diagram of a 4-CH LED driver, RT8510, used in notebook computers, is illustrated in Figure 2. The upper block is Boost Converter, providing the voltages needed for LED strings, and the lower block is Constant Current Dimming Controller.

Backlight Modules, as the lighting source of LCDs, consist of light sources, light guides and backlight diffuser plates, etc. As LCD TVs and laptops have become increasingly prevalent, the development focus is to incorporate energy-efficient LED backlight modules into the systems in response to the trend of large-scale and low-profile panels.

For edge-lit LED backlighting technology, white LEDs are placed around the four sides of the LCD, and the light is emitted through between the LCD panel and the reflector sheet, by which the light is reflected to the back of the LCD panel. The light guide plate spreads the light evenly across the back of the LCD. This is by far the most commonly used LED backlighting technology with advantages of low cost and low profile.

For direct-lit backlighting technology, LEDs are placed in a flat array behind the light guide plate and the LCD screen, which the light is directly emitted to. This method allows for fast locally dimming LEDs for specific areas of brightness on the screen to greatly enhance dynamic contrast. The disadvantage, however, is that more LEDs are to be used, which will then increase product cost and also the thickness of the backlight module. White LEDs are most commonly used for LED backlighting, while for some high-end models, RGB LEDs are used for wider-gamut color rendition.

1.LED Current Accuracy: LED current is set by the value of the external resister RISET connected from the ISET pin to ground. This current is mirrored by a current mirror to the current source. The error percentage of the current values from the theoretical calculation and the actual current is called as LED Current Accuracy.

2.LED Current Matching: There are many ways to configure LEDs in an array. If LED strings are connected in parallel, the LED current through each LED string must match with each other. This will increase the brightness uniformity among various LED strings. LED current usually is directly proportional to LED brightness.

3.Dimming Type: Dimming has become an essential feature of LED drivers. And it can be categorized into Analog Dimming and PWM Dimming. PWM Dimming can achieve better color rendition due to no shift in the chromaticity coordinates. However, it is more susceptible to audible noise problems. The approach to tackle this will be proposed in the later session.

4.LED Current Linearity: For PWM dimming, the output LED current varies with PWM duty cycle. The relationship between these two is described as linearity. The LED current linearity will become degraded for low PWM duty ratio and high PWM dimming frequency. Figure 4 displays the RT8510 PWM Dimming Linearity.

The commonly used power architecture for today’s TV models is that LLC or Flyback systems provide DC power supply to boost or buck converters, which then drive LED arrays, and LED Current Regulator clamps the current at the desired LED brightness. Nevertheless, in recent years, LED arrays can be found directly driven by an LLC or a Flyback system, while the voltage of the previous stage is adjustable by controller ICs.

Figure 5 is the application schematic diagram of a power solution. The RT8525, on the left-hand side, as a DC-DC Boost Converter, provides sufficient voltages to drive LED arrays. The RT8300, as a Current Regulator, provides constant current and dimming function. DHC (Dynamic Headroom Control) connects these two ICs as a feedback control. When the backlight module is turned on, the forward voltage, Vf, of the LED will decrease due to the increasing temperature. If the output voltage remains fixed, the terminal voltages on LED 1~4 pins will then increase. It will cause both the power dissipation and the temperature of the RT8300 to rise. Consequently, it will result in the decrease of overall efficiency and the failure of surface temperature requirement for the ICs. Therefore, there must be a mechanism to make the boost converter lower down its output voltage.

Dynamic Headroom Control (DHC) function is created for this purpose. The RT8300 will find out which channel has the lowest terminal voltage on LED 1~4 pins among all LED channels and will clamp the desired operating voltage by the curve in Figure 6. This voltage has a linear relationship with the LED current.

If the pin voltage for that lowest-voltage channel is higher than the corresponding value in Figure 6, the RT8300 VFB pin will be set high. Through R3 to VREF, the output voltage (VLED) will be lowered. Vice versa, if the pin voltage is too low, VFB pin will be set low and the output voltage will be pulled higher. Figure 7 shows the schematic and the corresponding equations, which are based on the Superposition Theorem.

For different applications, the wattages of their backlight modules will be different. Generally, the larger LCD panels, the more LED arrays to provide for the desired brightness will be needed. The power dissipations for ICs and power devices will thus be increased, which deteriorates the thermal performance. Compared to the power solutions for the backlights of notebook computers, the desktop monitors demand greater power. Therefore, it is better the MOSFETs are connected externally instead. For applications of even higher wattages, such as LCD TVs, even the drivers of current source devices will be connected externally in order to lower down the surface temperature of ICs. The following lists Richtek LED backlight power solutions for various applications.

All electronics products have specifications with regard to audible noises. When portable electronics products become more and more prevalent, the noise specifications for their backlight modules are even stricter. The audible noises usually arise when the applications operate in PWM dimming mode. The noises mainly results from the resonance, caused by the output capacitance, MLCC, and the output current switch. In PWM dimming, PWM LED current switches between heavy and zero loads. The abrupt changes of the loads will increase the ripples of the output voltage. Such ripples to human ears are audible noises. Figure 9 shows the waveform diagram of the RT8510 when dimming.

5.Use larger OVP resistors: When PWM is off, larger OVP resistors will lower the load and the output dropout voltage, and so the noises can be reduced.

6.Replace with an MLCC from the noise reduction solution: The output capacitance will affect how large the ripples are. Large ripples may cause resonance in between the layers, which will induce noises. The noise-reduction capacitors have the superior performance over the cross-voltages, that is, less capacitance change at higher DC biases. Figure 10 shows the comparison of the equivalent MLCC capacitances between the new (noise-reduction) and conventional fabrication processes.

1.SLP (Short LED Protection): If any LED(s) in the LED string is connected short when mounted on the surface, the overall forward voltage Vf of the LED string will be lower, which will results in higher VLEDX terminal voltage. SLP is to detect whether the VLEDX voltage is too high. For some models, only the short channel will be off, while for others, it is the driver circuit to be turned off. Users can adjust SLP voltage via RSLP.

2.OLP (Open LED Protection): If any LED(s) in LED strings are in poor contact, whether in assembly or in use, OLP is to detect whether the VLEDX voltage is too low when power-on, and will send out the warning signal accordingly.

3.OVP (Over Voltage Protection): When the overvoltage occurs at the output voltage, OVP will detect it by the voltage divider. It will clamp the output voltage at the voltage set by OVP, without turning off the circuitry. Figure 12 shows the RT8300 protection mechanism flow.

In 3D mode, due to the decreased PWM duty, the higher brightness from backlight modules is needed. The images perceived by human’s right/left eyes will be alternately displayed to generate the effect of field of depth. Figure 13 illustrates a 3D dimming functional diagram. The LED driver, RT-CVT, demands that the 3D-glasses shutters be synchronized with Main Board in order to effectively block left and right eyes alternately.

This approach is used for advanced models to enhance the contrast. The blacks with local dimming are perceived darker because the backlights of that section are dimmed. On the contrary, the backlights behind brighter sections can be brighter. Henceforth, local dimming has the advantage of consuming less power. Figure 14 illustrates an example of a 64-zone local dimming. The more zones the screen is divided into, the more noticeable the benefit of local dimming is. However, the trade-off is the complexity of control and cost will be correspondingly increased.

For local dimming applications, the limited bandwidth of the commonly used I2C Interface is no longer acceptable. For example, the RT8302, a 4-CH Programmable Current Sink Led Driver, uses the SPI Bus (Serial Peripheral Interface Bus) as the signal transmission interface instead. Figure 15 shows the RT8302 SPI interface application schematic diagram.

The architectures for LED backlight driving systems vary in accordance with various requirements, such as energy efficiency, cost down and performance enhancement. The driver ICs should then be changed accordingly. Furthermore, to power LED strings, the power solutions should change with the applications (TV/ Monitor/ Notebook/ Tablet). Finally, to tackle the audible noises, to enhance the system efficiency, and to meet the surface temperature requirements for all the components are also important aspects to consider for customers.

Most iPad/iPhone hardware operates at voltages between 1.8 V - 5.2 V. However, the backlight circuit operates at about 15 - 20 V. At this higher voltage, the backlight components are more prone to damage when a short circuit occurs. The high voltage backlight circuit is also prone to corrosion from water damage.

The backlight diode - Like the backlight filters, the backlight diode is a fragile component. In cases where a backlight filter is particularly burned up, you’ll often find that the diode has failed as well. Diode failure in the absence of filter damage is rare, but it can happen.

The most common cause of a self-induced short occurs from working on the device with the battery still connected. Even when the screen is dark, there is voltage in the backlight circuit. A slipped pair of tweezers or misalignment of the LCD connector can short the backlight circuit to ground. (The iPad mini is particularly prone to this fault, as simply removing or inserting the flex cable into its connector at a slight angle is enough to bridge the backlight’s high voltage pin to the adjacent ground pin.) Avoid self-induced shorts by always disconnecting the battery before working on a device.

Another cause of backlight shorts is faulty assembly procedures. iPhone screens have a soldered joint on the LCD flex cable connecting the thinner backlight flex cable that powers the LED light strip. During device fabrication, these solder joints are protected by piece of black tape—however, during the screen refurbishing process some manufacturers neglect to replace the tape, apply it misaligned, or fail to apply it securely. As a result, the screen initially works during testing—but once the metal LCD shield is installed, the exposed solder joints touch the grounded frame, shorting the backlight circuit.

Backlight shorts can occur when the latch for the ZIF connector securing the LCD flex is missing. The LCD flex slides out an angle and the high voltage backlight pin contacts the ground pin, causing a short circuit.

Water damage is a frequent source of backlight problems. Water will corrode the LCD connector pin/pad junction, which breaks the electrical path to the connector and can damage the filter.

Backlight circuit failure can also occur from damage to the electrical traces on the circuit board. If the electrical traces buried in the board are inadvertently severed—for example, from trying to fasten the board with too large a screw—the backlight circuit will not conduct power to the backlight LEDs.

To diagnose whether your device is “dead” or just has a malfunctioning screen, try connecting it to your computer. If the computer recognizes the device, then the problem probably resides with the LCD screen or backlight circuit. Additionally, iPhones will notify the user of a backlight problem by repeatedly playing a chime sound and vibrating.

The good news is that nearly all backlight failures are repairable. Once the damaged component is identified it can simply be replaced. If this isn’t something that you can do yourself, call a knowledgeable microsolder shop and send it out for a quick repair.

Most people think a dead LCD display means you have to replace the panel. This can be prohibitively expensive, and it’s usually cheaper just to buy a new TV or monitor. But unless there was physical damage to the screen, it’s rare for panels to break. More likely than not, your LED backlights are the culprit.

You won’t find backlights in all TVs. Plasma TVs forego them in favor of individual pixels. But if you bought a run-of-the-mill TV from a brand like Vizio, you have backlights. That’s a good thing! Backlit TVs can produce video that’s just a smidge less vibrant than other technology, for a significantly reduced price.

If you want to fix your TV, you’re going to need the right tools. In this case, that means getting your hands on a backlight tester for your LED lamp beads.

We’re about to review three of the best LED lamp bead TV backlight testers that money can buy. To find out how they stack up, we’ll need to take a close look at their designs and features. But if you don’t have time to read the whole guide, here’s a quick summary:

The TKDMR LED Lamp Bead TV Backlight Tester is small and compact. It measures 3.7 inches wide, 2.1 inches deep, and 1.1 inches thick. And at 8.8 ounces, it’s light enough to carry in your pocket. The housing is constructed from a white polymer, and seems durable enough for day-to-day use.

The front of the housing sports an LCD display, which shows the output voltage in bright red numerals. Beneath this are a set of specifications and helpful tips.

The TKDMR tester can accept an input voltage of between 85 and 265 volts. It can output this power at anywhere from 0 to 300 watts. In order to keep from overloading your LEDs, it won’t go to 300 watts all at once.

Instead, it will start at 0 watts when you touch the contacts with your leads. Then it will slowly ramp up power until it reaches an appropriate level. This is designed not to burn out individual diodes, which can sometimes be rated for as little as 5 volts. The working current of 0 to 30mA will be effective on the majority of TV backlights.

The SID LED Multipurpose Tester for LED TV Backlight is a bit beefier. The white plastic housing is 9.17 inches long, 6.34 inches wide, and 2.05 inches thick. And at 14.39 ounces, it tips the scales at nearly a pound. Needless to say, you’re not going to be carrying it around in your pocket.

At the front center of the housing is a large LED display. The top half shows your current output voltage in blue numerals. Beneath that, you’ll see the current milliamp level in red numerals. Beneath the display is a pair of blue dials, which you can operate with your fingers or a flathead screwdriver. These allow you to exercise precision control over both your voltage and your amperage.

The test leads plug into the right side of the housing. In addition to standard pin-style leads, there’s a set of right-angle leads for accessing awkwardly-positioned contacts. There’s also a KT4H connector, which will allow you to test your TV’s temperature controller as well as backlights. A separate switch controls the power to the test leads.

The input voltage can range from 85 to 265 volts. You can manually adjust the output voltage to between 0 and 330 volts. Or you can set the tester to automatic mode, where it will automatically ramp up. The amperage output can go as high as 150mA, which is enough for pretty much any TV. And like the output voltage, it can be set to automatic mode. There’s even a special circuit board testing mode that you can turn up to 999mA.

In addition to all this, the SID tester won’t burn out your LED light beads if you mix up the polarity. With most testers, you need to be careful not to confuse the anode and the cathode.

The KOET LED TV Backlight Tester is superficially similar to the TKDMR tester in many respects. To begin with, its white housing is very compact, at just 3.66 inches long, 2.36 inches wide, and 1.18 inches thick. It’s also the lightest of the bunch, weighing in at just 3.5 ounces. That’s less than a single McDonald’s hamburger patty.

The front of the housing is dominated by an LED display, with red numbers on a black background. This shows your current output voltage. The rest of the front of the housing has some branding and basic instructions, but nothing important.

This tester features automatic current and voltage adjustment, so you don’t need to be an expert to use it. The current automatically switches to 15mA or 30mA as needed for the job. The same goes for the output voltage, which goes from 0 to 300 volts. The accepted input voltage can range between 85 and 265 volts.

You might be surprised to learn that there are LEDs in your LCD TV. Isn’t the entire point of the TV that it uses LCD technology? The answer is yes… and no.

LCD is short for “liquid crystal diode,” which is the technology that gives HD and 4K TVs their color. However, the LCDs themselves don’t produce any light. The crystal in each pixel simply changes its shape to convert white light into different colors. Or, in the case of black, it absorbs the light to create a negative space. But the original white light has to come from somewhere.

Old-school LCD displays used cold-cathode fluorescent lamps (CCFLs). These were affordable and reliable, but not as efficient as LED lights. Worse, they contained mercury, which made disposal expensive and recycling dangerous. As LEDs became more affordable, manufacturers slowly made the switch. Since 2013, no major manufacturer has produced a CCFL-backlit LCD TV. Unless your TV is very old or a plasma TV, it almost certainly has LED backlighting.

LED backlights can be arranged in a few ways. In most TVs, the term “backlight” is actually a misnomer. Displays tend to use edge lighting – lights in the sides or bottom of the TV. Special reflectors inside the display spread the light around, creating a more or less uniform light distribution.

Some cheaper TVs will have fully-backlit TVs, with the lights arrayed behind the screen, facing the viewer. This actually produces a better image, but it makes the display significantly thicker. Higher-end TVs use full backlighting, but with a more complex set of reflectors that slim down the design.

In most cases, the LED diodes themselves don’t die. At least not until they’ve been used for tens of thousands of hours. The same goes for controllers, which can last for decades if they’re not abused. In most cases, there’s a problem with the LCD cable, fuse, power supply, or motherboard. A few pointers before you begin:

You’ll need the right tools. A TV backlight tester is ideal, since it won’t easily damage your diodes. That said, you can use any digital multimeter if you’re an experienced hand at electronics.

You need to be careful of the wires. You’ll have to open up the plastic tape on the sides of the panel that say “do not touch.” This doesn’t mean don’t touch anything. It means not to touch the ribbon cables that run along the board. These are the panel interface cables, and they’re very delicate.

Inside the TV, you’ll need to locate your LED light strip(s). Follow the cables from the strips, and you’ll find the controller where it meets the ribbon cable from the panel. At the controller, look for the following elements:

The voltage supply point – This can be tougher to find, but it’s typically labeled with the letter “F” followed by a number. Look for something like “F1” or “F2” with a small fuse connected to it.

The power controller – On different brands, this may say “BL_ON,” “ENA,” “ENAB,” or “LEDON.” This contact accepts a current of 5 volts or more, depending on the size of the display.

To test an individual diode, connect your tester to the backlight in parallel and slowly increase the current. If your tester is automatic, this will happen on its own. As you increase the power supply, the diode should eventually illuminate. If it doesn’t, you know it’s defective.

So, which one of these LED lamp bead TV backlight testers is the best? A lot depends on what you’re trying to do. You could make a good argument for any of them. That said, here are some of the things we’ve learned.

We started out by reviewing the TKDMR LED Lamp Bead TV Backlight Tester. This is a straightforward tester without any complex controls. In fact, the only control is the power switch. That said, the intelligent current adjustment does a great job of maintaining a safe output voltage. And while you can’t use it for every LED problem, the 30mA of current will be plenty for most jobs.

Second on our list was the SID LED Multipurpose Tester for LED TV Backlight. It’s a bit bigger and bulkier, but it has some benefits that the others don’t. For one thing, you can manually adjust the voltage and amperage. For another thing, you can output up to 150 amps, which makes it a lot more versatile. Finally, you don’t have to worry about LED diode polarization when you’re touching the contacts.

Bringing up the rear is the KOET LED TV Backlight Tester. This is the lightest of the three as well as the smallest. It also has automatic voltage and amperage adjustment, although there’s no way to make any manual changes. And with a grounded plug, you can feel a little bit more secure.

VDC combines both our internal design capabilities and our strong supplier relationships to offer LED driver solutions for ALL off-the-shelf and custom high brightness LED Back light solutions. VDC utilizes highly efficient LED Driver ICs and PWM dimming to properly drive each LED string. The constant current circuit design also provides the capability to easily customize the maximum or minimum brightness output required for each application.

For NVIS and High bright display designs, VDC designs a dual driver IC with smart communication. The High brightness control communications with the NVIS Mode control allowing for fail-proof operation. Our LED drivers are design and made in the USA. VDC Engineering can recommend or design the proper LCD Driver for any LCD or Custom Back light system. Just let us know what you need and our Engineers or Sales teams will give you the correct LED Driver, with all of the necessary cabling.