thermal management of lcd displays free sample

2023-01-03 12:32:11

LCD displays are commonly used today in devices that require information to be displayed in human-perceptible form. LCD displays are typically comprised of an enclosure, a LCD module, backlights and supporting electronics. Since LCD displays use thin depth LCD modules to display information as opposed to larger in depth cathode ray tube (CRT) displays for similar sized screens, LCD displays are often used in devices that have packaging and/or space constraints. Unlike LCD displays, the tube in a CRT display increases substantially in depth as the screen size increases.

Electronic devices, such as fuel dispensers and automatic teller machines (ATM) for example, use displays to display information to users of these devices. Such information may be instructions on how to use the machine or a customer"s account status. Such information may also include other useful information and/or services that generate additional revenue beyond the particular function of the device, such as advertising or newsworthy information. Through increasingly easier and cheaper access to the Internet, it has become even more desirable for electronic devices to use displays that are larger in screen size and employ higher resolution color graphics without substantially increasing the depth of the display due to packaging limitations. Therefore, LCD displays are advantageous to use in displays in electronic devices because of the thin nature of LCD modules.

LCD displays used in outdoor devices typically use an environmentally-sealed enclosure since LCD displays include internal components, such as electronics, backlights and display modules, whose operations are sensitive to outdoor conditions, such as water and dust. However, the backlights and the electronic circuitry generate extreme heat during their operation thereby raising the ambient air temperature inside the enclosure. The ambient temperature in the enclosure rises even more in outdoor devices due to sunlight heat. If the ambient temperature in the enclosure is not managed, components of the LCD display 10 may fail. For example, the LCD module may start to white or black out if the ambient temperature inside the enclosure rises above a certain temperature.

One method keeping the ambient air temperature lower inside the enclosure is to provide a larger enclosure so that it takes more heat generated by the internal components of the LCD display and external sources, such as the sunlight, to raise the ambient air temperature inside the enclosure. However, increasing the size of the enclosure is counter to the goal of using a thin depth enclosure for a LCD display.

Therefore, a need exists to provide a thin LCD display enclosure that is sealed from the environment and is capable of efficiently dissipating heat generated by the internal components of the LCD display and external heat, such as sunlight.

The present invention relates to a thermal management system for a liquid crystal display (LCD) that is placed inside a thin depth enclosure and may be incorporated into an outdoor device. The thermal management system efficiently transfers and dissipates heat in the ambient air of the LCD display enclosure generated by components of the LCD display and external heat, such as sunlight.

In one embodiment of the present invention, the LCD display comprises an environmentally-sealed, heat conducting enclosure with a backlight assembly having at least one backlight. The backlight assembly is connected to the inside rear portion of the enclosure. A heat sink is attached on the outside rear portion of the enclosure. Heat generated by the backlights is transferred using natural convection from the enclosure to the heat sink, and the heat sink dissipates such heat to the atmosphere.

In another embodiment of the present invention, the LCD display contains the backlight assembly as discussed in the preceding paragraph. The LCD display also contains a lens on the front portion of the enclosure and a LCD module between the lens and the backlight assembly. The LCD module is placed in between the top and bottom of the enclosure to provide air gaps inside and at the top and the bottom of the LCD module to form a circular airflow path around the LCD module. A fan is placed in the airflow path to forcibly move heated air inside the enclosure from the front of the LCD module to the rear portion of the enclosure for heat dissipation through the heat sink and to the atmosphere.

The LCD display may be placed in any type of electronic device, including but not limited to a kiosk, a fuel dispenser, a personal computer, an elevator display, and an automated teller machine (ATM). The LCD display may display information and other instructions to a user of an electronic device incorporating the LCD display. If the LCD display has a touch screen, the LCD display may also act as an input device.

FIG. 1 is a schematic diagram of one embodiment of a thin depth LCD display enclosure having a thermal management system according to the present invention;

The present invention relates to a thermal management system for a LCD display having a thin depth enclosure, and that may be placed in and outdoor environment and/or device. A thermal management system aids the LCD display 10 in overcoming the effects of internal heat generated by components of the LCD display 10 and heat from sunlight heat, if the LCD display 10 is placed in sunlight. The thermal management system also allows a thinner depth enclosure to be used for the LCD display. Use of a thin depth LCD display may be useful for addressing space and packaging issues for devices requiring a display.

A LCD display 10 according to one embodiment of the present invention is illustrated in FIG. 1. The LCD display 10 comprises an environmentally-sealed enclosure 12 that has a front portion 14 and a rear portion 16. The environmentally-sealed enclosure 12 protects the internal components of the LCD display 10 from external elements that may affect the proper operation, such as water, dust, etc. The enclosure 12 is constructed out of a heat conducting material, such as sheet metal, aluminum, or copper for example, so that heat generated by components of the LCD display 10 can be dissipated outside of the enclosure 12 to the atmosphere using convective heat transfer. In one embodiment, the depth of the enclosure 12 is approximately 40 millimeters.

The enclosure 12 includes a transparent lens 18 at the front portion 14 of the enclosure 12 for external viewing of the LCD display 10. The lens protects the internal components of the LCD display 10 and also allows the LCD module 26 to be viewed from outside of the enclosure 12. The lens 18 may be constructed out of clear plastic, glass, Plexiglas, or other transparent material so long as the LCD module 26 can be viewed from outside the enclosure 12. The LCD module 26 may be an active or passive matrix display, may include color, and may pass or block light to provide information for external viewing.

A backlight assembly 20 is provided in the rear portion 16 of the enclosure 12. The backlight assembly 20 holds one or more backlights 22. The backlights 22 project light towards the rear of the LCD module 26 so that the LCD module 26 can be properly viewed through the lens 18. In this particular embodiment, the backlights 22 are flourescent light bulbs. When power is provided to the backlights 22, light is projected from the backlights 22 towards the LCD module 26. The LCD module 26, depending on its design, either blocks the light or allows the light to pass through to display information for external viewing in human-perceptible form through the lens 18.

The LCD display 10 also includes a thermal management system for convectively moving and dissipating heat generated by internal components of the LCD display 10, such as the backlights 22 and electronic circuitry (not shown) in the enclosure 12, as well as external heat on the enclosure 12, such as sunlight. Heat generated by these sources raises the ambient air temperature inside the enclosure 12 thereby possibly causing the LCD display 10 to not function properly. Although the backlights 22 are designed to operate at higher temperatures, the heat generated by the backlights may affect the performance of the LCD module 26. For example, if the LCD module 26 is a color module, the color will start to fade as the ambient temperature inside the enclosure 12 increases beyond designed operating temperatures of the LCD module 26.

It may be desirable for a LCD display 10 in an outdoor device to be brighter than would otherwise be required in an indoor device due to light and glare created by sunlight. Increasing the brightness of the backlights 22 causes the backlights 22 to generate more heat and/or the power to the electronic circuitry to be greater. Because the enclosure 12 is environmentally-sealed, heat generated by the backlights 22, the electronic circuitry, and external sources needs to be dissipated outside of the enclosure 12 in order for the LCD module 26 to operate at a lower temperature. For example, some LCD modules 12 may need to be kept at temperatures at or lower than 70 degrees Celsius to operate properly. One solution is to reduce the power to the backlights 22 that in turn lowers the heat generated by the backlights 22, but this also reduces the brightness of the LCD display 10.

The present invention may be used to avoid having to reduce the brightness of the backlights 22. Heat generated by the LCD display 10 may be convectively dissipated in two manners. The LCD display 10 dissipates heat inside the enclosure 12 using one or more heat sinks 24 attached to the rear portion 16 of the enclosure 12. The heat sink 24 may contain one or more fins 25 to create greater surface area on the heat sink 24 for dissipation of heat. This heat sink 24 ensures that the internal surface temperature of the enclosure 12 is kept as close to the atmospheric temperature as possible to ensure that the heated air inside the enclosure 12 is absorbed by the enclosure 12. FIG. 1 illustrates the heat dissipated by the heat sink 24 to the atmosphere using arrows pointing upward on the outside of the rear portion 16 of the enclosure 12.

Heat generated by the backlights 22 is dissipated through the heat sink 24. The backlight assembly 20 is located against the surface of the rear portion 16 of the enclosure 12. In one embodiment, the center of the backlights is approximately 3.25 millimeters from the rear portion 16 of the enclosure 12. In this manner, heat generated by the backlights 22 is convectively transferred to the atmosphere, using natural convection. The heat generated by the backlights 22 is transferred to the rear portion 16 of the enclosure 12 and to the heat sink 24. The closer the heat sink 24 is to the backlights 22, the faster heat generated by the backlights 22 can be transferred outside of the enclosure 12 thereby reducing the chance of such heat to increase the ambient air inside the enclosure 12.

Heat generated by the backlights 22 that is not immediately dissipated through the rear portion 16 of the enclosure 12 and the heat sink 24 causes the ambient air temperature inside the enclosure 12 to rise. Heat generated by electronic circuitry inside the enclosure 12 and any external heat on the enclosure 12, such as sunlight, also causes the ambient air temperature inside the enclosure 12 to rise. To dissipate the heat in the ambient air, thereby cooling the LCD module 26, an airflow path 30 is created around the LCD module 26 by placement of the LCD module 26 between the lens 18 and the backlight assembly 20. In one embodiment of the present invention, the back of the LCD module 26 is placed approximately 12.9 millimeters from the backlights 22 to properly diffuse and evenly backlight the LCD module 26. The front of the LCD module 26 is placed approximately 9.4 millimeters from the lens 18 so that any protrusion on the lens 18 does not damage the LCD module 26. Spacing between the lens 18 and the LCD module 26 also allows air to be routed across the LCD module 26 for thermal management, as discussed below. The LCD module 26 is also placed between the top and bottom of the enclosure 12 in the vertical plane so that air gaps 28A and 28B are formed on the top and bottom of the LCD module 26. In this manner, air is free to flow around the LCD module 26 in a circular fashion, as illustrated by the counter-clockwise airflow arrows moving around the LCD module 26 in FIG. 1.

In order to dissipate heat in the ambient air in the enclosure 12, a fan 32 is placed in the airflow path 30. The fan 32 provides forced convection of the ambient air inside the enclosure 12 to the rear portion 16 of the enclosure 12 for dissipation. In one embodiment, the fan 32 is placed at the top of the enclosure 12 above the LCD module 26. During operation, that fan 32 rotates counter-clockwise to create the counter-clockwise circular airflow path 30. The ambient air is routed to the rear of the LCD module 26 and to the rear portion 16 of the enclosure 12 for dissipation through the enclosure 12 to the heat sink 24 and to the atmosphere.

The fan 32 may be any type of air movement device that can create the airflow path 30; however, one embodiment of present invention employs a laminar flow fan 32 manufactured by Delta Corporation. An example of such a laminar flow fan 32 is disclosed in U.S. Pat. No. 5,961,289 entitled “Cooling axial flow fan with reduced noise levels caused by swept laminar and/or asymmetrically staggered blades,” incorporated herein by reference in its entirety. A laminar flow fan 32 creates a sheet of air, rather than turbulent air, across the LCD module 26. The laminar airflow is more efficient than turbulent airflow for moving air and transferring heat from the front of the LCD module 26 to the rear portion 16 of the enclosure 12. A more efficient fan 32 allows selection of a fan 32 that is smaller in size since it may require less rotations of the fan 32 to move an amount of air desired and/or move the same amount of air in a smaller airflow path 30. Each of these factors contributes to a smaller fan 32 size that in turn contributes to a thinner depth enclosure 12. In one embodiment, the fan 32 operates at approximately 3400 revolutions per minutes (RPM). However, the present invention may use any type of fan 32, including those that generate turbulent air. The fan 32 speed may also be adjusted to move air in the desired manner and efficiency.

FIG. 2 illustrates one embodiment of a device that incorporates the LCD display 10 known as a “kiosk”34. A kiosk 34 is any type of interactive electronic device that provides an input device, an output device, or both. Kiosks 34 are typically used in retail environments to sell products and/or services to customers. Some common types of kiosk 34 include vending machines, fuel dispensers, automatic teller machines (ATM), and the like. FIG. 2 illustrates one example of a kiosk 34 that includes the LCD display 10 illustrated in FIG. 1 as an output device for displaying information. Soft keys 36 are located on each side of the LCD display 10 as an input device for customer selections; however, an input device may also take others forms, such as a keypad 38, touch screen keys on the LCD display 10 (not shown), card entry device, magnetic or optically encoded cards for example, voice recognition, etc. The LCD display 10 of the present invention is particularly suited for kiosks 34 that are located in outdoor environments where the enclosure 12 of the LCD display 10 is environmentally-sealed. However, the LCD display 10 may be placed in any type of kiosk 34 regardless of whether the kiosk 34 is placed in an outdoor environment.

FIG. 3 illustrates one embodiment of a communication architecture used for the LCD display 10. The LCD display 10 comprises a display CPU board 40 that contains electronics and software. In this particular embodiment, the display CPU board 40 contains a single display microprocessor 42 and display software 44. The display software 44 contains both volatile memory 46, such as RAM and/or flash memory, and non-volatile memory 48, such as EPROM and/or EEPROM. The display software 44 contains program instructions for the display microprocessor 42 and may also contain information to be displayed on the LCD module 26. The display microprocessor 42 may also manages information received from external sources and controls the operation of the LCD module 26.

In this embodiment, information is communicated from one or more external devices to the display microprocessor 42 to then be displayed on the LCD module 26. A main controller 50 is provided as the interface to the display microprocessor 42. The main controller 50 may be any type of control system, including a point-of-sale system for example. The main controller 50 may be coupled to more than one display microprocessor 42 for managing multiple LCD modules 26. The main controller 50 may also be connected to a local server 56, located in close proximity to the LCD display 10, that sends information to be displayed on the LCD module 26. A remote server 52, located remotely from the LCD display 10, may also be provided to send information to the LCD module 26. The remote server 52 may send information over a network 54 directly to the display microprocessor 42, through the main controller 50, and/or through the local server 56 to be eventually displayed on the LCD module 26. The remote server 52, the local server 56, the main controller 50, and the display microprocessor 42 may be coupled each other through either a wired or wireless connection or network 54 using any type of communication technology, including but not limited to the Internet, serial or parallel bus communication, radio-frequency communication, optical communication, etc.

Examples of Internet information management that may be used with the present invention to send information to a LCD display 10 and/or communicate information entered into a LCD display 10 having a touch screen or other electronic device incorporating an LCD display 10 are disclosed in U.S. Pat. Nos. 6,052,629 and 6,176,421 entitled “Internet capable browser dispenser architecture” and “Fuel dispenser architecture having server” respectively, both of which are incorporated herein by reference in their entirety.

FIG. 4 illustrates another exemplary outdoor device that may incorporate the LCD display 10 of the present invention known as a “fuel dispenser” 60. A fuel dispenser 60 may also be considered a type of kiosk 34 depending on its configuration and features. The illustrated fuel dispenser 60 contains a LCD display 10 for providing instructions and/or information to a customer at the fuel dispenser 60. The fuel dispenser 60 is comprised of a housing 62 and at least one energy-dispensing outlet, such as a hose 64 and nozzle 66 combination, to deliver fuel to a vehicle (not shown). As illustrated in FIG. 2, the fuel dispenser 60 may have other input and/or output devices for interaction with a customer, such as price-per-unit of fuel displays 72, soft-keys 36, a receipt printer 68, a radio-frequency identification (RFID) antenna 74, and a cash acceptor 70.

Also note that the LCD display 10 may also be placed external to the fuel dispenser 60 and attached to the fuel dispenser 60 as disclosed in co-pending patent application entitled “Multiple browser interface,” filed on Apr. 23, 2001.

Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. It should be understood that the present invention is not limited to any particular type of component in the LCD display 10 including, but not limited to the enclosure 12, the lens 18, the backlight 22 and backlight assembly 20, the heat sink 24, the LCD module 26, and the fan 32. Additionally, the LCD display 10 may be used in any type of device having or using a display, including but not limited to a personal computer, a kiosk 34, an elevator, an ATM, and a fuel dispenser 60. Also for the purposes of this application, couple, coupled, or coupling is defined as either a direct connection or a reactive coupling. Reactive coupling is defined as either capacitive or inductive coupling.

One of ordinary skill in the art will recognize that there are different manners in which these elements can accomplish the present invention. The present invention is intended to cover what is claimed and any equivalents. The specific embodiments used herein are to aid in the understanding of the present invention and should not be used to limit the scope of the invention in a manner narrower than the claims and their equivalents.

thermal management of lcd displays free sample

Liquid crystal displays (LCD) have become an essential component to the industry of display technology. Involved in a variety of contexts beyond the indoors like LCD TVs and home/office automation devices, the LCD has expanded its usage to many environments, such as cars and digital signage, and, thus, many temperature variations as well.

As with any substance that requires a specific molecular characteristic or behavior, LCDs have an operating temperature range in which the device, if within, can continue to function properly and well. In addition to that, there is also an ideal storage temperature range to preserve the device until used.

This operating temperature range affects the electronic portion within the device, seen as falling outside the range can cause LCD technology to overheat in hot temperatures or slow down in the cold. As for the liquid crystal layer, it can deteriorate if put in high heat, rendering it and the display itself defective.

In order for the LCD panel to avoid defects, a standard commercial LCD’s operation range and storage range should be kept in mind. Without adaptive features, a typical LCD TV has an operating range from its cold limit of 0°C (32°F) to its heat limit of 50°C (122°F) (other LCD devices’ ranges may vary a bit from these numbers).

The storage range is a bit wider, from -20°C (-4°F) to 60°C (140°F). Though these ranges are quite reasonable for many indoor and even outdoor areas, there are also quite a few regions where temperatures can drop below 0°C or rise above 32°C, and in these conditions, LCDs must be adapted to ensure functionality.

Heat, can greatly affect the electronics and liquid crystals under an LCD screen. In consideration of heat, both external heat and internally generated heat must be taken into consideration.

Seen as the liquid crystals are manipulated in a device by altering their orientations and alignments, heat can disrupt this by randomizing what is meant to be controlled. If this happens, the LCD electronics cannot command a certain formation of the liquid crystal layer under a pixel, and the LED backlighting will not pass through as expected, which can often lead to dark spots, if not an entirely dark image. This inevitably disrupts the display’s readability.

Depending on the upper limit of the operation temperature range, LCD device can be permanently damaged by extreme heat. With long exposure to extreme heat, besides the destruction of the liquid crystals, battery life can shorten, hardware can crack or even melt, response time may slow to prevent even more heat generation from the device.

The LED backlight and the internal circuitry, typically TFT-based in the common TFT LCDs, are components that can generate heat that damages the device and its display. To address this concern with overheating, many devices use cooling fans paired with vents.

But this leads to another problem: how can moisture be prevented from entering through the vent? If moisture enters the device and high heat is present, condensation can occur, fogging the display from inside, and in some cases, short-circuiting may cause the device to turn off. In order to circumvent this issue, the shapes of the air vents are specific in a way that allows only for air movement, not forms of moisture.

In the opposite direction is extreme cold. What typically occurs in the cold is “ghosting” (the burning of an image in the screen through discoloration) and the gradual slowing and lagging of response times. Like heat-affected LCD modules, the extreme temperature can affect the liquid crystals. This layer is a medium between the liquid and solid state, so it is still susceptible to freezing.

An LCD device can be left in freezing temperatures because it will likely not be permanently damaged like in the heat, but it is important to understand the device’s limits and how to take precautions when storing the device. The standard and most common lower-bound storage range limit is -20°C, below freezing, but if possible, it would be best to keep it above that limit, or else there is still a risk of permanent damage.

Display types have a lot of variation. Choices like alphanumeric or graphic LCD, human-machine interactive LCD modules and touchscreen panels capabilities, the width of the viewing angle, level of contrast ratios, types of backlighting, and liquid crystal alignment methods are often considered. For example, the twisted nematic LCD provides for the fastest response time at the lowest cost, but cannot offer the highest contrast ratio or widest viewing angle.

Environment-based factors must consider things besides the obvious temperature like UV exposure and humidity/moisture, as they all are necessary in finding the perfect fit extreme temperature LCD module.

Besides the LCD modules, recent new products have opened doors in wide temperature range displays, such as OLED displays. OLED displays offer better displays in regard to contrast, brightness, response times, viewing angles, and even power consumption in comparison to traditional LCD displays.

These benefits, in addition to its ability to achieve a wide temperature range, provide more options for consumers in search of high quality displays for extreme climates.

The use of liquid crystal displays (LCDs) in user interface assemblies is widespread across nearly all industries, locations, and operating environments. Over the last 20 years, the cost of LCD displays has significantly dropped, allowing for this technology to be incorporated into many of the everyday devices we rely on.

The odds are high you are reading this blog post on a laptop or tablet, and it’s likely the actual screen uses LCD technology to render the image onto a low-profile pane of glass. Reach into your pocket. Yes, that smartphone likely uses LCD technology for the screen. As you enter your car, does your dashboard come alive with a complex user interface? What about the menu at your favorite local drive-thru restaurant? These are some everyday examples of the widespread use of LCD technology.

But did you know that the U.S. military is using LCD displays to improve the ability of our warfighters to interact with their equipment? In hospitals around the world, lifesaving medical devices are monitored and controlled by an LCD touchscreen interface. Maritime GPS and navigation systems provide real-time location, heading, and speed information to captains while on the high seas. It’s clear that people’s lives depend on these devices operating in a range of environments.

As the use of LCDs continues to expand, and larger screen sizes become even less expensive, one inherent flaw of LCDs remains: LCD pixels behave poorly at low temperatures. For some applications, LCD displays will not operate whatsoever at low temperatures. This is important because for mil-aero applications, outdoor consumer products, automobiles, or anywhere the temperature is below freezing, the LCD crystal’s performance will begin to deteriorate. If the LCD display exhibits poor color viewing, sluggish resolution, or even worse, permanently damaged pixels, this will limit the ability to use LCD technologies in frigid environments. To address this, there are several design measures that can be explored to minimize the impact of low temperatures on LCDs.

Most LCD displays utilize pixels known as TFT (Thin-Film-Transistor) Color Liquid Crystals, which are the backbone to the billions of LCD screens in use today. Since the individual pixels utilize a fluid-like crystal material as the ambient temperature is reduced, this fluid will become more viscous compromising performance. For many LCD displays, temperatures below 0°C represent the point where performance degrades.

Have you tried to use your smartphone while skiing or ice fishing? What about those of you living in the northern latitudes - have you accidently left your phone in your car overnight where the temperatures drop well below freezing? You may have noticed a sluggish screen response, poor contrast with certain colors, or even worse permanent damage to your screen. While this is normal, it’s certainly a nuisance. As a design engineer, the goal is to select an LCD technology that offers the best performance at the desired temperature range. If your LCD display is required to operate at temperatures below freezing, review the manufacturer’s data sheets for both the operating and storage temperature ranges. Listed below are two different off-the-shelf LCD displays, each with different temperature ratings. It should be noted that there are limited options for off-the-shelf displays with resilience to extreme low temperatures.

For many military applications, in order to comply with the various mil standards a product must be rated for -30°C operational temperature and -51°C storage temperature. The question remains: how can you operate an LCD display at -30°C if the product is only rated for -20°C operating temperature? The answer is to use a heat source to raise the display temperature to an acceptable range. If there is an adjacent motor or another device that generates heat, this alone may be enough to warm the display. If not, a dedicated low-profile heater is an excellent option to consider.

Made of an etched layer of steel and enveloped in an electrically insulating material, a flat flexible polyimide heater is an excellent option where space and power are limited. These devices behave as resistive heaters and can operate off a wide range of voltages all the way up to 120V. These heaters can also function with both AC and DC power sources. Their heat output is typically characterized by watts per unit area and must be sized to the product specifications. These heaters can also be affixed with a pressure sensitive adhesive on the rear, allowing them to be “glued” to any surface. The flying leads off the heater can be further customized to support any type of custom interconnect. A full-service manufacturing partner like Epec can help develop a custom solution for any LCD application that requires a custom low-profile heater.

With no thermal mass to dissipate the heat, polyimide heaters can reach temperatures in excess of 100°C in less than a few minutes of operation. Incorporating a heater by itself is not enough to manage the low temperature effects on an LCD display. What if the heater is improperly sized and damages the LCD display? What happens if the heater remains on too long and damages other components in your system? Just like the thermostat in your home, it’s important to incorporate a real-temp temperature sensing feedback loop to control the on/off function of the heater.

The first step is to select temperature sensors that can be affixed to the display while being small enough to fit within a restricted envelope. Thermistors, thermocouples, or RTDs are all options to consider since they represent relatively low-cost and high-reliability ways to measure the display’s surface temperature. These types of sensors also provide an electrical output that can be calibrated for the desired temperature range.

The next step is to determine the number of temperature sensors and their approximate location on the display. It’s recommended that a minimum of two temperature sensors be used to control the heater. By using multiple sensors, this provides the circuit redundancy and allows for a weighted average of the temperature measurement to mitigate non-uniform heating. Depending on the temperature sensors location, and the thermal mass of the materials involved, the control loop can be optimized to properly control the on/off function of the heater.

Another important consideration when selecting a temperature sensor is how to mount the individual sensors onto the display. Most LCD displays are designed with a sheet metal backer that serves as an ideal surface to mount the temperature sensors. There are several types of thermally conductive epoxies that provide a robust and cost-effective way to affix the delicate items onto the display. Since there are several types of epoxies to choose from, it’s important to use a compound with the appropriate working life and cure time.

For example, if you are kitting 20 LCD displays and the working life of the thermal epoxy is 8 minutes, you may find yourself struggling to complete the project before the epoxy begins to harden.

Before building any type of prototype LCD heater assembly, it’s important to carefully study the heat transfer of the system. Heat will be generated by the flexible polyimide heater and then will transfer to the LCD display and other parts of the system. Although heat will radiate, convect, and be conducted away from the heater, the primary type of heat transfer will be through conduction. This is important because if your heater is touching a large heat sink (ex. aluminum chassis), this will impact the ability of the heater to warm your LCD display as heat will be drawn toward the heat sink.

Insulating materials, air gaps, or other means can be incorporated in the design to manage the way heat travels throughout your system on the way toward an eventual “steady state” condition. During development, prototypes can be built with numerous temperature sensors to map the heat transfer, allowing for the optimal placement of temperature sensors, an adequately sized heater, and a properly controlled feedback loop.

Before freezing the design (no pun intended) on any project that requires an LCD display to operate at low temperatures, it’s critical to perform low temperature first. This type of testing usually involves a thermal chamber, a way to operate the system, and a means to measure the temperature vs time. Most thermal chambers provide an access port or other means to snake wires into the chamber without compromising performance. This way, power can be supplied to the heater and display, while data can be captured from the temperature sensors.

The first objective of the low-temperature testing is to determine the actual effects of cold exposure on the LCD display itself. Does the LCD display function at cold? Are certain colors more impacted by the cold than others? How sluggish is the screen? Does the LCD display performance improve once the system is returned to ambient conditions? These are all significant and appropriate questions and nearly impossible to answer without actual testing.

As LCD displays continue to be a critical part of our society, their use will become even more widespread. Costs will continue to decrease with larger and larger screens being launched into production every year. This means there will be more applications that require their operation in extreme environments, including the low-temperature regions of the world. By incorporating design measures to mitigate the effects of cold on LCD displays, they can be used virtually anywhere. But this doesn’t come easy. Engineers must understand the design limitations and ways to address the overarching design challenges.

A full-service manufacturing partner like Epec offers a high-value solution to be able to design, develop, and manufacture systems that push the limits of off-the-shelf hardware like LCD displays. This fact helps lower the effective program cost and decreases the time to market for any high-risk development project.

thermal management of lcd displays free sample

The pace of development in the electronics and telecommunication fields has been accelerating in all aspects of the business. For example, electronics/telecommunications equipment has traditionally been housed in large buildings, smaller buildings (sheds) and outdoor cabinets. The introduction of electronics to the outdoor environment has imposed serious constraints on enclosure design since temperature and humidity are the two major causes of electronics failure. Since most electronic systems do not include environmentally hardened designs, the enclosure must provide an environment in which they can survive. Among the equipment/systems involved are displays such as LCD, LED and other monitors.

The use of LEDs (Light Emitting Diodes) has been increasing exponentially in the last few years. In the beginning, heat dissipation was not a worrisome problem because of the low power the LED’s used. However, their power consumption and their useful life and reliability are dependent on how their temperature can be controlled, especially in view of high-power LEDs used for illumination and outdoor signage applications. The most important goal in LED cooling is to maintain junction temperature (Tj, the temperature at the p-n junction) from rising above prescribed levels since the junction temperature is a good predictor of the useful life of the LED component. In addition, the junction temperature in many cases must be kept relatively constant since fluctuations and shifts affect the intensity and the color of the LED light output. From a thermal standpoint, junction temperature, as with many other electronic components and systems, is influenced by power levels, heat sinking (high conductivity materials, convection cooling, extended surfaces, heat spreading, heat pipes, etc), ambient temperature, interface materials, applied pressures (clamping to reduce thermal contact resistance).

Thermal management of LEDs can range from the use of natural convection to the use of liquid cooling loops that allow for far higher heat removal rates than employing gases as the cooling medium. Air natural and forced convection, up to very recently, have been the cooling methodology of choice when cooling with a fluid. At the system level, and especially for outdoor applications, liquid cooling is normally not suitable; therefore, only cooling solutions that use natural or forced air convection are employed such as fans, blowers, air-to-air heat exchangers, air-conditioners and other passive cooling techniques.

What is more, display devices such as monitors have incorporated LED technology and must also be thermally managed outdoors since they require hardened enclosures to carry out their tasks.

The objective here is to cover the thermal management of LEDs at the system level, both discrete LED modules or outdoor enclosures (LED walls or LED monitors). This assumes that LED and board level thermal management has been dealt with separately. Nowadays, enclosures that contain LEDs are being installed in various environmental conditions. Most will be fitted with either air conditioning/thermoelectric cooling or air-to-air heat exchangers as needed because of relatively high heat dissipation requirements; for lower heat generation levels, flow-through fan cooling is sufficient. For example, there has been an unprecedented growth of the application of LEDs for outdoor (and indoor) signage or video systems such as sports displays, advertising billboards, and gas station pump customer information displays. These all are enclosures with one wall comprised of LEDs. In addition, recently LED display monitors have been installed in outdoor enclosures and therefore require thermal management. Figure 1 shows an illustration of these two types of enclosures.

The goal is to maintain peak temperatures in the enclosures below a certain level that is normally prescribed (the lowest junction temperature of the LED components) by the manufacturers. Humidity levels are of concern, but since most enclosures are either sealed or its temperatures are much higher than the air’s dew points, humidity is generally not a problem (after the transient effect of opening/closing the enclosure is eliminated.)

The designer should be aware that the air temperatures within the enclosures will be a function of: the amount of heat generated by all the electronic equipment in the enclosure; the amount of heat generated by auxiliary and cooling equipment (fans, etc.); ambient conditions (outdoor air), particularly temperature, solar radiation, wind speeds, etc.; objects surrounding the enclosure (shading, ground reflections, buildings, trees, etc.); enclosure design (surface area, shape, paint’s radiation characteristics, etc.) and air exchange with the outside air, either passive by infiltration, or active by fans or blowers.

Let us consider an enclosure that has installed LED equipment that dissipates a certain amount of heat. The first step is always to realize that the design temperature is that temperature that the enclosure air will attain when there is heat balance, or in equation form:

where, Qequipment comprises the LEDs and its electronics heat dissipation, Qsolar load is the solar heat load and Qcooling-system is the amount of heat removed by the cooling system. The solar load is a complicated term because it includes contributions from all modes or heat transfer. For example:

Normally, the value of Qradiated will always be positive (towards enclosure) but the other two can be either positive or negative, depending on the enclosure’s temperature. Thus, if Qbalance is not zero, this means that the temperature inside the enclosure is either higher/lower than the set temperature and the enclosure is losing/gaining heat by convection and conduction.

Furthermore, since incident solar radiation varies during the daylight hours, the designer must decide whether to conduct a steady state or transient analysis. Moreover, since Qradiation is a very complex term that includes, among other effects, solar declination, latitude, time of year, solar azimuth, atmospheric absorption, atmospheric clearness, re-radiation from other walls, buildings, ground etc., and incident wall surface properties, some simplifying measures must be taken into account. The result is that one can effectively double or triple the amount of heat flux being added into the enclosure depending on the calculation method. The calculation of the cooling load is carried out using several methods. One of these methods is the ASHRAE’s cooling load calculation methods. Normally, when calculating cooling loads, one would include a) Space heat gain, b) Space cooling load, and c) Space heat extraction rate. Space heat gain is the rate at which heat enters or is generated within the space at any given instant. This includes for the enclosure heat transferred into the conditioned space from the external walls and roof due to solar radiation, convection and temperature differential.

One normally includes instantaneous solar radiation effects and delayed effects. The delayed effects include the slow build-up of energy that the external walls accumulate as they absorb solar radiation. This happens because walls are normally thick and massive; making energy absorbed important. For LED enclosures this is not included since its walls are thin (at the most 3 cm when insulation might be added) and should not be included. Another component of heat gain is latent heat due to moisture infiltration. For sealed LED outdoor enclosures, the power electronics are kept in an airtight enclosure with negligible contribution.

where, α -absorptance of solar radiation surface, It – total solar radiation [W/m2], ho– coefficient of heat by long wave radiation and convection [W/K-m2], ε – hemispherical emittance, and ΔR a radiation correction factor [W/m2]. Figure 2 shows typical Sol-Air temperatures for various latitudes.

For roofs: ΔR =63 W/m2, for walls: ΔR = 0, for dark surfaces, α/It = 0.052, which is the maximum value for any surface. To calculate heat transfer into the conditioned space,

where U is the overall heat transfer coefficient for the wall and A is the surface area for the wall. The term, U, includes convective and radiation effects by the internal and external airflow (See AHSHRAE’s Fenestration Chapter for more details, ASHRAE, 1981, 1986) and the wind outside, in addition to conduction through the walls. The solar load calculated will be added to the equipment load to find the total cooling load. The solar load will include three surfaces that can be illuminated simultaneously, with the roof always included.

Display/signage enclosures have evolved. Typical LED system design has been the display shown in Figure 3. They typically were metal enclosures measuring 5-10 m wide, 250 mm deep and 5 m high. These enclosures could have thousands of LEDs each measuring, typically,5- 8 by 5-8 by 3 mm and dissipating an average of 1W each, all installed on the largest vertical wall. Therefore, the total amount of heat dissipation for this enclosure (including the electronics needed to control and manage the LEDs) could reach thousands of Watts. Figure 3 shows a CFD model of this enclosure using Phoenics by CHAM Ltd of the UK.

In the last few years, display outdoor enclosures are also being designed to house various display signage equipment configurations such as LED monitors with dissipating heat rates ranging from 200 to 1500 W, depending on the size and type of auxiliary equipment. These enclosures are installed in various environmental conditions, and typically the enclosures, without major structural modifications, may be fitted with fans, air conditioning or air-to-air heat exchangers as needed. Figure 4 shows at typical enclosure (CFD model).

Equipment housed in these enclosures include TV LED monitors that have been initially designed for indoor use and have been slightly hardened to be placed in a hot, dry environment without the support of an enclosure. Many manufacturers sell these monitors.

The goal of the designer is to maintain the peak temperatures in the enclosures, which are below a certain level that is normally prescribed by the electronic equipment manufacturer. Humidity levels are also of concern, but since in most enclosures, its temperatures are much higher than the air’s dew points, humidity is generally not an issue (after the transient effect of opening and closing the enclosure is eliminated). However, typically, the LED monitors are not fully outdoor rated, that is they must be protected from rain and moisture, therefore they must be installed in IP55/56/66 enclosures.

Most enclosures need to be designed to keep the system operating with slight internal overpressure. Cooling air is guided to flow into a gap between the LED screen surface and external transparent wall guided by guide-vanes, and the cooling system also must allow for air to flow to the rest of the enclosure, in addition to the flow in the LED/Wall gap. Overpressure is used to maintaining IP55 and IP66 design and a fan and filter inlet system construction allows for proper solar mitigation technology. For further solar mitigation purposes, if used, a solar shield overhang can reduce solar loading.

Finally, of paramount importance is to keep the LED surface (especially when in full solar exposure) under a maximum temperature. For the above LED monitor, this temperature is 110 C. Since, maximum solar radiation for latitudes below 35 N or S can generate surface temperatures higher than 110 C, then a typical construction would involve a gap between the outdoor facing glass plane and the LED monitor (see Figure 5).

thermal management of lcd displays free sample

Taking into account the conditions inherent to digital billboards and multimedia kiosks, particularly for outdoor, the ventilation and thermal management of the equipment ensure the normal and correct functioning of all components – in addition to avoiding their deterioration.

PARTTEAM & OEMKIOSKS, aware of the importance of temperature and ventilation systems, seeks to ensure maximum efficiency and reliability in all its products. In this sense, this article seeks to explain the importance of thermal management and ventilation.

The requirements of an internal environment are easy to understand, since there is total control of the environment and a certain stability. This makesdigital billboardsor indoormultimedia kiosksdon’t need as much care as outdoor equipment. However, outdoors, there are other attentions that should be taken care of, being the primary element of this system the control of temperature. Moreover, PARTTEAM & OEMKIOSKS has a proprietary system – CROXTHERM® – for thermal management and display cooling.

Temperature management ensures that all system components function correctly. Through this management, stains are prevented, more specifically when the temperature on the screen surface is high; good levels of performance are guaranteed and a long life of the integrated components is ensured.

Although it is important to ensure that any outdoor display can withstand the weather, it is equally important to ensure that it withstands the varying temperatures of an outdoor environment.

Both cold and heat affect LCD displays. Therefore, it is important to consider thermal management, since it protects the equipment from the outside temperature, ensuring image quality, low power consumption and component conservation.

Therefore, it is important to make an adequate thermal management. There are techniques that can be adopted to avoid the degradation of the components, such as:

The temperature of an outdoor display varies between 0 and 50ºC – this is the guaranteed maintenance temperature. An ambient temperature (approximately 25ºC and involving an active cooling system) or the normal operating temperature (which varies between 10 and 40ºC) can also be used. Within this last one, heat or cold don’t affect the display.

Equally important, PARTTEAM & OEMKIOSKS sun protection foils offer several advantages throughout the year, adapting to both the exterior and interior. In addition to being able to control light, they ensure thermal optimization. In other words, they allow better insulation in winter and a significant reduction of heat in summer.

A glass covered with these sunscreen foils can prevent infrared radiation, controlling peaks of light and reducing them to a level pleasing to the human eye. This creates an effective protection for the equipment, which brings several advantages:

Faced with the fact that outdoor kiosks are subject to adverse environmental conditions that can affect the performance of sensitive electronic components – from extreme temperatures to humidity and dust –, this equipment must be prepared to maintain its internal temperatures, regardless of climate.

For indoor kiosks, extreme temperatures are less risky, so the ambient temperature tends to remain constant. Often, these kiosks maintain their temperature through convection ventilation. However, if the structure is overheated, a fan can be used to dissipate the heat from the electronic components and the upper ventilation of the kiosk.

The ventilation systems cool the components of an equipment, guaranteeing the quality of the air that circulates and preventing the infiltration of pollutant gases, bacteria and humidity. Therefore, these systems are vital for the normal operation of the equipment and its components.

This effect is controlled in all projects, studying the location and positioning of the equipment in order to analyze the position of the sun during the day and to understand if it will harm its use.

For a good functioning of our kiosks, an efficient and correctly tested ventilation is essential. Perfect air circulation must be guaranteed at all times. For this reason, air inlet and outlet flows must be measured at regular intervals. Our tests with flow rate meters are ideal for obtaining this guarantee.

One of the most effective ways to avoid the heating of a digital signage equipment is through the use of air conditioning, which regulates the air temperature according to the billboard’s temperature.

In this case, if there is no “connection” with the exterior – other than through air conditioning – the entrance of humidity, dust and water is avoided.

Studies have shown that electronic components tend to last longer if temperatures remain low. But there are other factors in the structure that must be considered, such as the risk of condensation and energy costs.

In fact, the important thing is to maintain a stable temperature and not necessarily low in the equipment. The ideal recommended temperature is approximately 25°C, protecting the components, minimizing the risk of condensation and reducing energy costs.

Thermoelectric cooling uses the Peltier effect to transfer heat from one side of the device to the other. It can be used for heating or cooling (although, in practice, cooling is the main application).

In order to combat the high temperatures in some locations, PARTTEAM & OEMKIOSKS kiosks are covered with thermal insulation. That is, they are prepared to allow a lower heat exchange, so that the external heat is not felt inside the kiosk and the cooling system has a higher efficiency.

At PARTTEAM & OEMKIOSKS, the equipment is designed with intensive quality testing. Firstly, a study is carried out taking into account the heat dissipation of the components and the place where they will be installed – analyzing the average ambient temperature and sun exposure.

On the factory floor, the kiosks are placed inside a greenhouse with projected heat sources – where they stay for several hours –, and this test is monitored through data collected by sensors scattered over several areas of the kiosk. The objective is to understand if the heat is becoming concentrated and putting in question the functioning of some component.

Tests are also performed with cooling and ventilation systems to see if the correct system is being used. If necessary, a readjustment is made during the assembly process to ensure the proper functioning of the equipment.

thermal management of lcd displays free sample

Taking into account the conditions inherent to digital billboards and multimedia kiosks, particularly for outdoor, it can be said that the key element of these systems is, besides ventilation, temperature control.

Strongly recommended, the thermal management of the equipment ensures the normal and correct functioning of all components – besides avoiding their deterioration.

PARTTEAM & OEMKIOSKS, aware of the importance of temperature and ventilation systems, seeks to ensure maximum efficiency and reliability in all its products.

Therefore, outside, there are other attentions that must be taken, being the primordial element of this system the control of the temperature. Moreover, PARTTEAM & OEMKIOSKS has a proprietary system – CROXTHERM® – for thermal management and display cooling.

Junction temperature: The junction temperature is the active region of the LED. This is where electrons jump between the two semiconductors to produce photons. A low junction temperature helps LEDs to produce more light. The junction temperature is affected by current, thermal path and ambient temperature.

Although it is important to ensure that any outdoor display can withstand the weather, it is equally important to ensure that it withstands the varying temperatures of an outdoor environment.

In a structure, in case the relative humidity of the air is 80% and the temperature is 30ºC, the air will contain approximately 25 milliliters of water. If the temperature drops to 15ºC, the air will contain about 13 milliliters with the same humidity.

The other 12 milliliters condense. At first it may not seem like much, but with the natural movement of air, this amount is concentrated in the coolest parts of the equipment.

PARTTEAM & OEMKIOSKS sun protection foils offer several advantages throughout the year, adapting to both the exterior and interior. In addition to being able to control light, they ensure thermal optimization. In other words, they allow better insulation in winter and a significant reduction of heat in summer.

A glass covered with these sunscreen foils can prevent infrared radiation, controlling peaks of light and reducing them to a level pleasing to the human eye. This creates effective protection for the equipment.

The ventilation systems cool the components of an equipment, guaranteeing the quality of the air that circulates and preventing the infiltration of pollutant gases, bacteria and humidity.

This effect is controlled in all projects, studying the location and positioning of the equipment in order to analyze the position of the sun during the day and to understand if it will harm its use.

In this case, if there is no “connection” with the exterior – other than through air conditioning – the entrance of humidity, dust and water is avoided.

thermal management of lcd displays free sample

Digital InfiniteTouch™ | All-glass multi-touch p-cap interactive touch screen with the capability to report 60,000 simultaneous touch points over the active area of display at a 300Hz refresh rate

To evaluate the performance of display devices, several metrics are commonly used, such as response time, CR, color gamut, panel flexibility, viewing angle, resolution density, peak brightness, lifetime, among others. Here we compare LCD and OLED devices based on these metrics one by one.

A fast response time helps to mitigate motion image blur and boost the optical efficiency, but this statement is only qualitatively correct. When quantifying the visual performance of a moving object, motion picture response time (MPRT) is more representative, and the following equation should be used

From Figure 5, we can gain several important physical insights: (1) Increasing the frame rate is a simple approach to suppress image motion blur, but its improvement gradually saturates. For example, if the LC response time is 10 ms, then increasing the frame rate from 30 to 60 fps would significantly reduce the MPRT. However, as the TFT frame rate continues to increase to 120 and 240 fps, then the improvement gradually saturates. (2) At a given frame rate, say 120 fps, as the LC response time decreases, the MPRT decreases almost linearly and then saturates. This means that the MPRT is mainly determined by the TFT frame rate once the LC response time is fast enough, i.e., τ≪Tf. Under such conditions, Equation (1) is reduced to MPRT≈0.8Tf. (3) When the LC response is <2 ms, its MPRT is comparable to that of an OLED at the same frame rate, e.g., 120 fps. Here we assume the OLED’s response time is 0.

The last finding is somehow counter to the intuition that a LCD should have a more severe motion picture image blur, as its response time is approximately 1000 × slower than that of an OLED (ms vs. μs). To validate this prediction, Chen et al.

If we want to further suppress image blur to an unnoticeable level (MPRT<2 ms), decreasing the duty ratio (for LCDs, this is the on-time ratio of the ba

thermal management of lcd displays free sample

You Might Also Be Interested In