CA2747724A1 - Thermal control system for an electronic display - Google Patents

Abstract

A cooling assembly for an electronic image as-sembly and a display assembly containing the same. Some em-bodiments use ambient gas to cool power modules and/or an image assembly (sometimes backlight). Other embodiments use a closed loop of circulating gas which passes across the front surface of an image assembly and through a heat ex-changer. An open loop passes through the heat exchanger and extracts heat from the circulating gas. Ambient air may be used as the ambient gas. An optional additional channel may be used to cool the back portion of the image assembly or backlight with ambient gas. Some embodiments also use ther-mally conductive plates and ribs to distribute the heat and avoid hot spots in the display. The cooling assembly can be used with any type of electronic assembly for producing an image.

Description

Thermal Control System for an Electronic Display Inventors: William Dunn, Tim Hubbard, Ware Bedell Technical Field [0001] The exemplary embodiments generally relate to cooling systems and in particular to cooling systems for electronic displays.

Background of the Art [0002] Conductive and convective heat transfer systems for electronic displays generally attempt to remove heat from the electronic components in a display through as many sidewalls of the display as possible. In order to do this, the systems of the past have relied primarily on fans for moving internal air within the housing past the components to be cooled and out of the display. These components are typically power supplies. In some cases, the heated air is moved into convectively thermal communication with fins.

[0003] While such heat transfer systems have enjoyed a measure of success in the past, improvements to displays and new display applications require even greater cooling capabilities. In particular, cooling devices for electronic displays of the past have generally used convective heat dissipation systems that function to cool only the rear interior portion of the display. When used outdoors or in other warm environments, this is not adequate, especially when radiative heat transfer from the sun through a front display surface becomes a major factor. In many applications 200 Watts or more of power through a front display surface is common. Furthermore, the market is demanding larger screen sizes for displays. With increased electronic display screen size and corresponding front display surface size more heat will be generated and more heat will be transmitted into the displays. Also, when displays are used in outdoor environments the ambient air may contain contaminates (dust, dirt, pollen, water vapor, brake dust, sand, smoke, etc.) which, if ingested into the display for cooling the interior can cause damage to the interior components of the display.

[0004] Modern displays (especially those which are used outdoors) have become increasingly brighter, with some backlights producing 1,000-2,000 nits or more. In order to produce this level of brightness, illumination devices such as CCFL
assemblies, LEDs, organic LEDs, and plasma assemblies may produce a relatively large amount of heat. Further, the illumination devices require a relatively large amount of power in order to generate the required brightness level. This large amount of power is typically supplied through one or more power supplies for the display. These power supplies may also become a significant source of heat for the display.

[0005] A large fluctuation in temperature is common when devices of the past are used in outdoor environments, direct sunlight, or other difficult thermal environments.
Such temperature fluctuation adversely affects both the lifetime and the performance of the electronic components in these devices.

Summary of the Exemplary Embodiments [0006] While the systems of the past have attempted to remove heat only through the non-display sides and rear components of an electronic display, a preferred embodiment may cause convective heat transfer from the front face of the image assembly as well (the side which faces an intended viewer). These preferred embodiments may comprise two separate flow paths for gas through an electronic display. A first flow path may be a closed loop and a second flow path may be an open loop. The closed loop path travels across the front surface of the image assembly, continues to the rear of the display where it may enter a heat exchanger, finally returning to the front surface of the image assembly. The open loop path draws gas (ex. ambient air) through the rear of the display (possibly through a heat exchanger) and then exhausts it out of the display housing. A heat exchanger may be used to transfer heat from the closed loop to the open loop and exhausted out of the display.
Optionally, the open loop may also be forced behind the image assembly (sometimes a backlight other times an OLED or other type of image-producing assembly), in order to cool the image assembly and/or backlight assembly (if a backlight is necessary for the particular type of display being used). A cross-flow heat exchanger may be used in an exemplary embodiment.

[0007] Other embodiments relate to a system for cooling the following portions of an electronic display, either alone or in combination: (1) power module(s), (2) backlight, and (3) front display surface. Power modules with heat dissipating assemblies (ex. cold plates and/or heat sinks) may be used with some embodiments where the side of the power module containing the heat dissipating assembly is placed in the path of ambient gas while the side of the power module containing sensitive electrical components remains in a separate environment. An isolating structure may provide the necessary gaseous (and sometimes particulate/contaminate) isolation between the two sides of the power modules. The closed loop may or may not be used when cooling the power modules with an open loop of ambient gas.

[0008] Backlights with a front and rear sides may be used with some embodiments for LCD displays where the front side contains the illumination devices and the rear side contains a thermally conductive surface for dissipating the heat from the illumination devices. Ideally, there should be a low level of thermal resistance between the front and rear sides of the backlights.

[0009] Other embodiments may place the power modules in thermal communication with a plurality of thermally conductive ribs where the ribs are placed in the path of cooling air (sometimes ambient gas). The heat from the power modules is distributed throughout the ribs and removed by the cooling air. It has been discovered that forcing air through the relatively narrow channels defined by the ribs improves the ability to remove heat from the power modules.

[0010] In another embodiment, both the power modules and the display backlight (or image assembly) are in thermal communication with the ribs. In this way, a single path of cooling air (sometimes ambient gas) can be used to cool two of the warmest components of a typical electronic display. For example, and not by way of limitation, LED arrays are commonly used as the illumination devices for LCD displays. It has been found that the optical properties of LEDs (and other illumination devices) can vary depending on temperature. Thus, when an LED is exposed to room temperatures, it may output light with a certain luminance, wavelength, and/or color temperature.

However, when the same LED is exposed to high temperatures, the luminance, wavelength, color temperature, and other properties can vary. Thus, when a temperature variation occurs across an LED backlight (some areas are at a higher temperature than others) there can be optical inconsistencies across the backlight which can be visible to the observer. By using the embodiments herein, heat buildup can be evenly distributed across the ribs and removed from the display. This can prevent any potential `hot spots' in the backlight which may become visible to the observer because of a change in optical properties of the illumination devices (sometimes, but not always LEDs). In other embodiments, the image assembly (rather than a backlight) is in thermal communication with the ribs. The image assembly may comprise any form of electronic assembly for generating an image, including but not limited to: LCD, light emitting diode (LED), organic light emitting diode (OLED), field emitting displays (FED), light-emitting polymers (LEP), plasma displays, and any other flat/thin panel displays.

[0011] The ribs may provide an isolated chamber from the rest of the display so that ambient air can be ingested and used to cool the ribs. This is beneficial for situations where the display is being used in an outdoor environment and the ingested air may contain contaminates (pollen, dirt, dust, water, smoke, etc.) that would damage the sensitive electronic components of the display.

[0012] If a backlight is used with the particular display application, a backlight with front and rear sides may be used where the front side contains the illumination devices and the rear side contains a thermally conductive surface for dissipating the heat from the illumination devices. Ideally, there should be a low level of thermal resistance between the front and rear sides of the backlights. An exemplary embodiment contains a metal core PCB with LEDs on the front side and a metallic surface on the rear side.

[0013] By the aspects described below, the exemplary embodiments herein have made consistent cooling possible for large electronic displays, even in hot climates and placed in direct sunlight. The embodiments also do not require any form of air conditioner (although it may be used if desired), which reduces the space and energy requirements for the display.

[0014] The foregoing and other features and advantages of the exemplary embodiments will be apparent from the following more detailed description of the particular embodiments of the invention, as illustrated in the accompanying drawings.

Brief Description of the Drawings [0015] A better understanding of an exemplary embodiment will be obtained from a reading of the following detailed description and the accompanying drawings wherein identical reference characters refer to identical parts and in which:

[0016] FIGURE 1 is a perspective view of a typical power module;

[0017] FIGURE 2 is a perspective view of two power modules installed within an isolating structure;

[0018] FIGURE 3 is a perspective view of an embodiment where the cooling air may be used to cool the power modules and a backlight assembly;

[0019] FIGURE 4 is a perspective view of an embodiment which is similar to that which was shown in Figure 3 with the exception that a heat sink is now being used with the power modules;

[0020] FIGURE 5 shows a perspective view of an embodiment where a plurality of channels are created between the backlight assembly and the isolating structure;

[0021] FIGURE 7 shows a perspective section view of another embodiment which uses a thermally-conductive plate and thermally-conductive ribs;

[0022] FIGURE 8 shows a perspective section view of another embodiment where the ribs are used to distribute heat from and cool a backlight assembly;

[0023] FIGURE 9 is a rear perspective view of an embodiment where the rear cover of the display has been removed;

[0024] FIGURE 10A is a perspective section view of another embodiment showing the closed loop and open loop channels;

[0025] FIGURE 10B is a perspective section view similar to the view shown in Figure 10A where the rear and side covers have been removed;

[0026] FIGURE 11 is a perspective section view of another embodiment showing inlet and exhaust apertures for the ambient gas which is used only within the heat exchanger and not within additional optional channels; and [0027] FIGURE 12 is a perspective section view of an exemplary embodiment where a cross-flow heat exchanger is used to separate high power and low power electrical assemblies.

Detailed Description [0028] FIGURE 1 shows one embodiment of a typical power module 7 which may be used with some of the embodiment described herein. A printed circuit board 6 may be attached to the power module 7 and may contain a plurality of electronic components 5 which may be necessary to operate and control the power module 7. These electronic components 5 may include, but are no means limited to resistors, capacitors, op-amps, wire harnesses, connectors, and inductors. A baseplate 8 may be attached to the power module 7 and may act as a heat dissipating assembly for the power module 7, such that heat which is generated by the power module 7 is transferred to the baseplate 8. In some embodiments there may be more components used, such as a conductive pad located between the power module and the baseplate 8. Also, as discussed further below, any type of heat sink or fin assembly may be used with the baseplate 8 to further enhance its thermodynamic properties. There may be conductive pads placed between the baseplate 8 and a heat sink assembly also.

[0029] FIGURE 2 shows two power modules installed within an isolating structure 9 which substantially prevents gaseous and contaminate communication between the two sides of the power module. The baseplates 8 of the power modules are shown on the side of the isolating structure 9 where surrounding-environment cooling air 4 is designed to pass over the baseplates 8. Gaskets 11 may be used to provide a gaseous (and/or contaminate) seal between the power modules and the isolating structure 9. Cooling air 4 is sometimes drawn from the environment surrounding the display. This environment may contain harmful contaminates which could damage various electrical components in the display. These harmful contaminates include, but are not limited to: dust, smoke, pollen, water vapor, other harmful particulate and other harmful gases. Thus, one of the purposes for the isolating structure 9 is to prevent the surrounding-environment cooling air 4 from contacting some of the sensitive electronic components of the display, including but not limited to the electronic components 5 (shown in Figure 1) which are required to operate and control the power modules. By mounting the power modules within the isolating structure 9, surrounding-environment cooling air 4 can be drawn into the display housing and forced over the baseplates 8 (and optional heatsinks and fins) in order to cool the power modules. This can be accomplished without exposing sensitive electronic components to the potentially harmful surrounding-environment cooling air 4.

[0030] FIGURES 3 and 4 show embodiments where the cooling air 4 may be used to cool the power modules and a backlight assembly 140. These embodiments show a backlight assembly 140 which contains a plurality of illumination devices (ex.
LEDs) 141 which are mounted to a printed circuit board (PCB). An exemplary embodiment would use a metal core PCB or any other mounting structure which would have a relatively low level of thermal resistance so that heat can transfer from the illumination devices 141 to the rear surface of the backlight assembly 140 where it can be removed by the cooling air 4. The illumination devices 141 could be LED, halogen, CCFL, or any other device which produces light. Further, a backlight assembly may not even be necessary for some embodiments such as plasma, OLED, LEP, or FED displays. However, these display types are also known to generate heat and where backlight cooling is described in this application these methods could also be applied to the cooling of rear surfaces of these electronic image assemblies. Thus, where backlight assemblies are shown, a plasma, OLED, FED, or LEP image assembly could be substituted. The electronic components 5 may be isolated from the cooling air 4 by using the isolating structure 9.

[0031] FIGURE 4 shows an embodiment which is similar to that which was shown in Figure 3 with the exception that a heat sink 12 is now in thermal communication with the power modules in order to further facilitate the transfer of heat away from the power modules. It should of course be noted that many types of heat sinks are available which are made of many different materials and have many different geometry types.

Any form of heat sink is particularly contemplated with various embodiments and may be used to satisfy different operating conditions.

[0032] FIGURE 5 shows another embodiment where a plurality of channels 15 are created between the backlight assembly 140 and the isolating structure 9.
Channel separators 16 may be used to separate each channel 15 and provide structural rigidity to the overall assembly. The channel separators 16 would preferably be fabricated out of thermally conductive material so that they may also transfer heat between the backlight assembly 140 and the isolating structure 9. A thermally conductive channel separator 16 can also extract heat from either the backlight assembly 140 or the isolating structure 9 and may dissipate the heat into the air moving through the channel 15. Thus, some channel separators 16 may contain fins or heat sinks in order to facilitate heat transfer to the air moving through the channel 15.

[0033] FIGURE 6 shows a view down a single channel 15 which contains the heat sink 12 for a power module which is mounted within the isolating structure 9.
Some channels 15 may contain power modules and others may not. A channel fan 17 may be used to draw air through the channel 15 in order to cool the heat sink 12 (if used) and the channel separators 16 (if thermally conductive) as well as the backlight 140 (or LED assembly for an LED display). Each channel 15 may contain one or more channel fans 17. Some channels may not contain a fan at all, but may rely solely on natural convection to allow heat to rise and exit the channel. As will be discussed at length below, the fans can be placed anywhere in the display assembly and may be used to draw air through the channels, push air through the channels, or a combination of both.

[0034] While the display is in operation, the channel fans 17 may run continuously.
Alternatively, temperature sensing devices (not shown) may be placed in each channel and used to measure the temperature within the channel or any of the channel components (backlight or display assembly, isolating structure, or channel separators).
Based on data received from these temperature sensing devices, the various fans may be selectively engaged depending on which channel requires cooling. Thus, fans which draw air through channels 15 which contain power modules may run more often or at higher speeds due to the greater amount of heat coming from the power modules.

Also, channels which contain power modules may contain larger fans or a plurality of fans in order to cool the channel.

[0035] FIGURE 7 shows another embodiment which uses a thermally-conductive plate 10 and ribs 18. In one embodiment, the baseplate 8 of the power module would be in thermal communication with the thermally-conductive plate 10. In other embodiments, a baseplate 8 may not be used and instead, the power module 7 would be in direct thermal communication with the thermally conductive plate 10. Due to the thermally-conductive nature of the plate 10 and ribs 18 and the thermal communication between them, heat which is produced by the power modules would be distributed throughout the plate 10 and ribs 18. In an exemplary embodiment, a path of cooling air 20 (ambient gas) is used to remove the heat which has accumulated on the plate and ribs 18. Alternatively, a natural convection process could also be used to allow the heat to escape the plate 10 and ribs 18.

[0036] A plurality of mounting posts may be used to mount electronic assemblies such as PCBs, hard drives, timing and control boards, inductors, and even the power modules if desired. The mounting posts may also be thermally conductive so that the heat which is generated by these electronic assemblies can also be transferred to the plate 10 and the ribs 18 and removed by the cooling air 20.

[0037] In an exemplary embodiment, the plate 10 would provide a gaseous and contaminate barrier between the side containing the ribs 18 (and cooling air 20) and the side containing the mounting posts, power modules, and any other electronic assemblies. If the plate 10 provides an adequate barrier, ambient air may be ingested as cooling air 20 and the risk of contaminates entering the side of the plate containing the sensitive electronic components may be reduced or eliminated.
An inlet aperture 25 may be used to accept the cooling air 20 and direct it along the ribs 18.

[0038] The ribs 18 shown in this embodiment contain a hollow rectangular cross-section, but this is not required. Other embodiments may contain ribs with I-beam cross-sections, hollow square cross-sections, solid rectangular or solid square cross-sections, `T' cross-sections, `Z' cross-sections, corrugated or honeycomb cross-section, or any combination or mixture of these. It is preferable that the ribs 18 are thermally conductive. Metal may be used to produce the ribs 18 in some embodiments.

[0039] FIGURE 8 shows another embodiment where the ribs 18 are used to distribute heat from and cool a backlight assembly. The backlight assembly in this embodiment includes a plurality of illumination devices 32 which are mounted on a thermally conductive substrate 30. In an exemplary embodiment, the illumination devices would be LEDs and the thermally conductive substrate 30 would be a PCB and more preferably a metal core PCB. On the surface of the thermally conductive substrate 30 which faces the ribs 18 there may be a thermally conductive surface 35. In an exemplary embodiment, the thermally conductive surface 35 would be metallic and more preferably aluminum. It is preferred that the ribs 18 are in thermal communication with the rear surface 35 and that the rear surface 35 is in thermal communication with the thermally conductive substrate 30. In some embodiments however, the thermally conductive substrate 30 may comprise traditional PCB materials rather than a metal core PCB or any highly thermally conductive materials. It is most preferable that there is a low level of thermal resistance between the illumination devices 32 and the ribs 18.
Cooling air 20 may again be forced along the ribs 18 in order to remove heat from the backlight assembly. Of course, this could also occur through natural convection, but more efficient cooling has been typically observed through forced convection.
An image assembly (such as an OLED display which may not utilize a backlight) could also be used in place of the backlight assembly in order to cool the image assembly.

[0040] As noted above, many illumination devices (especially LEDs and OLEDs) may have performance properties which vary depending on temperature. When `hot spots' are present within a backlight or illumination assembly, these hot spots can result in irregularities in the resulting image which might be visible to the end user.
Thus, with the embodiments described herein, the heat which may be generated by the backlight assembly can be distributed throughout the various ribs and thermally-conductive surfaces to remove hot spots and cool the backlight.

[0041] In an exemplary embodiment, the ribs 18 may be used to cool both the backlight assembly and the power modules. In a further exemplary embodiment, the ribs 18 can also be used to cool any additional electronic assemblies by placing them in thermal communication with the thermally-conductive plate 10. Thus, with the ribs 18 in a central location, the `front' would be towards an intended observer of the display while the `back' would be on the opposite side of an intended observer. Therefore, the front side of the ribs 18 would be in thermal communication with a backlight assembly (or other illumination or image-producing assembly) and the rear side of the ribs would be in thermal communication with a rear plate (i.e. thermally-conductive plate 10). A single path of cooling air can then be used to cool the interior of the display while the various hot spots can distribute heat throughout the ribs and other thermally conductive surfaces to provide the most efficient cooling. This can be accomplished without having to expose sensitive electrical components to the contaminates and/or particulate of ambient gas.

[0042] FIGURE 9 shows the rear of an exemplary electronic display 100, where the rear cover for the display housing has been removed in order to show the internal components. In this embodiment, fan assemblies 102 and 103 for a closed loop of circulating gas may be placed along two opposing edges of a heat exchanger 101.
Preferably, fan assembly 102 is the inlet for the heat exchanger and fan assembly 103 is the exit for the heat exchanger 101. These assemblies can optionally be reversed however, where fan assembly 103 is the inlet and fan assembly 102 is the exit.
Further, both assemblies 102 and 103 are not required. Some embodiments may use only one fan assembly for the closed loop of circulating gas. If only one fan assembly is used, it is preferable to place the fan assembly at the inlet of the heat exchanger 101, so that the circulating gas is `pulled' across the front of the image assembly and pushed through the heat exchanger 101. This is not required however; other embodiments may pull the isolated gas through the heat exchanger 101. Other embodiments may push the isolated gas across the front of the image assembly. Fan assemblies 104 and 105 for an open loop of ambient gas may be placed along two opposing edges of the display housing. Again, both assemblies 104 and 105 are not required as some embodiments may use only one assembly and may use the open loop fan assemblies in a push or pull design. Therefore, when referring to the placement of the various fan assemblies, the terms `push', `pull', `force', and `draw' will be used interchangeably and any orientation may be used with the various embodiments herein.

[0043] The circulating gas which is being forced by the closed loop fan assemblies is primarily circulating around the display. For example, the circulating gas travels in a loop where it contacts the front surface of the image assembly (see Figures 10A-10B) and transfers heat from the image assembly to the circulating gas. The circulating gas is then preferably directed (or forced, pulled, etc.) into the heat exchanger 101 in order to transfer heat from the circulating gas to the ambient gas. Afterwards, the circulating gas exits the heat exchanger 101 and may return to the front surface of the image assembly. The circulating gas may also pass over several electronic components in order to extract heat from these devices as well. The electronic components may be any components or assemblies used to operate the display including, but not limited to: transformers, circuit boards, resistors, capacitors, batteries, power modules, motors, inductors, illumination devices, wiring and wiring harnesses, lights, thermo-electric devices, and switches. In some embodiments, the electrical components may also include heaters, when the display assembly might be used in cold-weather environments.

[0044] In order to cool the circulating gas (as well as optionally cooling a backlight assembly or image assembly as taught above) ambient gas is ingested into the display housing by the open loop fan assembly 104 and/or 105. The ambient gas may simply be ambient air which is surrounding the display 100. In some embodiments, the ambient gas may be air conditioned prior to being drawn into the display by one or more air conditioning assemblies (not shown). Once the ambient gas is ingested into the display, it may be directed (or forced) through the heat exchanger 101 and optionally also across the rear surface of the backlight assembly or image assembly (see Figures 10A-1 OB) or though ribs/channels as shown above or across power modules as shown above. By using the heat exchanger 101, heat is transferred from the circulating gas to the ambient gas. The heated ambient gas is then expelled out of the display housing.

[0045] Although not required, it is preferable that the circulating gas and ambient gas do not mix. In a preferred embodiment, the heat exchanger 101 would be a cross-flow heat exchanger. However, many types of heat exchangers are known and can be used with any of the embodiments herein. The heat exchanger 101 may be a cross-flow, parallel flow, or counter-flow (tube-within-a-tube or otherwise) heat exchanger. In an exemplary embodiment, the heat exchanger 101 would be a cross-flow and would be comprised of a plurality of stacked layers of thin plates. The plates may have a corrugated or honeycomb design, where a plurality of channels or pathways travel down the plate length-wise. The plates may be stacked such that the directions of the pathways are alternated with each adjacent plate, so that each plate's pathways are substantially perpendicular to the pathways of the adjacent plates. Thus, gas may enter the heat exchanger only through plates whose channels or pathways travel parallel to the path of the gas. Because the plates are alternated, the closed loop and ambient gases may travel in plates which are adjacent to one another and heat may be transferred between the two gases without mixing the gases themselves (if the heat exchanger is adequately sealed, which is preferable but not required).

[0046] In an alternative design, an open gap may be placed in between pairs of channelized or honeycomb plates. The open gap may travel in a direction which is perpendicular to the channels of the plates. This open gap may be created by running two strips of material or tape (esp. very high bond (VHB) tape) between two opposite edges of the plates in a direction that is perpendicular to the direction of the channels in the adjacent plates. Thus, gas may travel through the open gap (parallel to the strips or tape) but would not pass through the open gap in a direction which is perpendicular to the strips or tape (parallel to the channels of the adjacent plates).

[0047] Other types of cross-flow heat exchangers could include a plurality of tubes which contain the first gas and travel perpendicular to the path of the second gas. As the second gas flows over the tubes containing the first gas, heat is exchanged between the two gases. Obviously, there are many types of cross-flow heat exchangers and any type would work with the embodiments herein.

[0048] An exemplary heat exchanger may have plates where the sidewalls are relatively thin so that heat can easily be exchanged between the two paths of gas. A
plurality of materials can be used to create the heat exchanger. Preferably, the material used should be corrosion resistant, rot resistant, light weight, and inexpensive. Metals are typically used for heat exchangers because of their high thermal conductivity.
However, it has been discovered that plastics and composites can also satisfy the thermal conditions for electronic displays. An exemplary embodiment would utilize polypropylene as the material for constructing the plates for the heat exchanger. It has been found that although polypropylene may seem like a poor thermal conductor, the large amount of surface area relative to the small material thickness, results in an overall thermal resistance that is low. Thus, an exemplary heat exchanger would be made of plastic and would thus produce a display assembly that is thin and lightweight.
Specifically, corrugated or honeycomb plastic may be used for each plate layer.

[0049] As mentioned above, both inlet and exit fan assemblies are not required for the embodiments. Alternatively, only a single fan assembly may be used for each loop.
Thus, only an inlet fan assembly may be used with the closed loop and only an exhaust fan assembly may be used with the open loop. Alternatively, one of the loops may have both inlet and exit fan assemblies while the other loop only has either an inlet or exit assembly.

[0050] The gas used in both loops can be any number of gaseous matters. In some embodiments, air may be used as the gas for both loops. Preferably, the gas which travels through the closed loop should be substantially clear, so that when it passes in front of the image assembly it will not affect the appearance of the image to a viewer.
The gas which travels through the closed loop should also be substantially free of contaminates and/or particulate (ex. dust, dirt, pollen, water vapor, smoke, etc.) in order to prevent an adverse effect on the image quality and damage to the internal electronic components. It may also be preferable to keep the gas within the open loop from having contaminates. An optional filter (not shown) may be used to ensure that the air (either in the closed or open loop) stays free of contaminates. However, in an exemplary embodiment the open loop may be designed so that contaminates could possibly be present within the ambient gas but this will not harm the display.
In these embodiments, the heat exchanger (and the optional path behind the image assembly or backlight or through the ribs) is properly sealed so that any contaminates in the ambient gas would not enter sensitive portions of the display. Thus, in these exemplary embodiments, ingesting ambient air for the ambient gas, even if the ambient air contains contaminates, will not harm the display. This can be particularly beneficial when the display is used in outdoor environments or indoor environments where contaminates are present in the ambient air.

[0051] FIGURE 10A shows a cross-section of another embodiment of a display 200.
In this figure, the rear cover 250 and side covers 251 and 252 are shown to illustrate one method for sealing the overall display 200. The image assembly 220 is shown near the front of the display 200. As discussed above, the image assembly 220 may comprise any form of electronic assembly for generating an image, including but not limited to: LCD, light emitting diode (LED), organic light emitting diode (OLED), field emitting displays (FED), light-emitting polymers (LEP), plasma displays, and any other flat/thin panel displays. The front display surface 221 is placed in front of the image assembly 220, defining a channel 290 through which the circulating gas may flow. The front display surface 221 may be any transparent material (glass, plastic, or composite) and may comprise several layers for polarizing light, reducing glare or reflections, and protecting the internal display components. In an exemplary embodiment, the front display surface 221 would comprise two panes of glass which are laminated together with optical adhesive (preferably index-matching). Further, a polarizing layer may be attached to one of the panes of glass in order to reduce the internal reflections and solar loading on the image assembly 220. It is most preferable that the polarizing layer be attached to the inner surface of the front display surface 221 (the one facing the closed loop channel 290) and also contain an anti-reflective (AR) coating.

[0052] For the embodiment shown in Figure 10A, the image assembly 220 may be an LCD stack with a backlight assembly 222. Some backlights may use cold cathode fluorescent lamps (CCFLs) to produce the illumination necessary for generating an image. In an exemplary embodiment, the backlight assembly 222 would comprise a printed circuit board (PCB) with a plurality of LEDs (light emitting diodes) on the front surface. As discussed above, an exemplary embodiment would have a low level of thermal resistance between the front surface of the backlight assembly 222 and the rear surface 223 of the backlight. A metallic PCB may be used for this purpose. The rear surface 223 of the backlight may contain a thermally conductive material, such as a metal. Aluminum may be an exemplary material for the rear surface 223. A
second surface (or plate) 224 may be placed in close proximity behind the rear surface 223 of the backlight assembly 222. The space between the rear surface 223 of the backlight and the second surface 224 may define an additional optional open loop channel through which ambient gas may travel in order to cool the backlight assembly 222. This open loop channel 225 may be similar to the channel 15 shown above, except open loop channel 225 may be narrower.

[0053] FIGURE 10B shows the same cross section from Figure 10A with the rear cover 250 and side covers 251 and 252 removed and the closed and open loop air flows shown for explanatory purposes. The closed loop fan assembly 202 is used to propel the circulating gas 210 around the closed loop. A first open loop fan assembly 203 may be used to draw ambient gas 211 through the heat exchanger 201.
Optionally, a second open loop fan assembly 204 may be used to draw ambient gas 212 through the optional channel 225 for cooling the backlight assembly 222.
The optional second open loop fan assembly 204 can also be used to exhaust ambient gas which has traveled through the heat exchanger 201 and through the channel 225.
If a second open loop fan assembly 204 is not used, the first open loop fan assembly 203 may be used to exhaust the ambient gas 211 that has traveled through the heat exchanger 201.

[0054] As noted above, in an exemplary embodiment the ambient gas does not mix with the circulating gas. It may be important for the image quality that the circulating gas remains free of particulate and contaminates as this gas travels in front of the image assembly 220. Since gas for the open loop may contain various contaminates, a preferable embodiment should be adequately sealed to prevent the gas from the two loops from mixing. This is not necessary however, as filters (either removable or permanent) may be used to minimize the effect of particulate for both the open and closed loops.

[0055] FIGURE 11 is a perspective section view of another embodiment of a display assembly 600 showing inlet 60 and exhaust 65 apertures for the ambient gas 20.
The inlet aperture 60 may contain a screen or filter (removable or permanent) to remove any particulate (although this may not be necessary). One or more fans 50 may be used to draw the ambient gas 20 into the inlet aperture 60 and through the heat exchanger 201.
In this embodiment, the ambient gas 20 is only drawn through the heat exchanger 201 and not through any additional optional channels or ribs. This embodiment may be used when the display assembly 80 (or backlight assembly) does not require the additional cooling of an additional channel. For example, and not by way of limitation, this embodiment 600 may be used when an OLED is used as the image assembly 80.
Further, this embodiment 600 may be used when the LCD backlight is not generating large amounts of heat because it is not required to be extremely bright (perhaps because it is not used in direct sunlight). Still further, this embodiment may be used when the ambient gas 20 contains particulate or contaminates which may damage the display. In these situations, it may be desirable to limit the exposure of the display to the ambient gas 20. Thus, in these situations it may be desirable to only ingest ambient gas 20 into the heat exchanger 201 and not through any additional cooling channels.

[0056] In some embodiments, the ambient gas 20 may be air conditioned (or otherwise cooled) before it is directed into the heat exchanger 201. A front display surface 221 may be used to create an anterior (front) wall of the channel 290 and/or protect the image assembly 80 from damage. An exemplary front display surface may be glass. Another embodiment for the front display surface 221 may be two panes of glass which are laminated together using optical adhesive. Solar loading (radiative heat transfer from the sun through the front display surface 221 may result in a heat buildup on the image assembly 80 (ex. OLED or LCD assembly). This heat may be transferred to the circulating gas, where this heat may then be transferred to the ambient gas 20 and expelled from the display. The image assembly could be any one of the following: LCD, plasma display assembly, OLED, light emitting polymer (LEP) assembly, organic electro luminescence (OEL) assembly, or LED display assembly.

[0057] FIGURE 12 shows an exemplary embodiment where a circulating gas 400 is forced between a front display surface 221 and an image assembly 80 and then through a heat exchanger 201 in order to remove at least a portion of the heat absorbed from the image assembly 80 and front display surface 221. The circulating gas 400 may be propelled by a closed loop fan assembly 410. The heat exchanger 201 may accept circulating gas 400 in one direction while accepting ambient gas 310 in a substantially perpendicular direction such that heat may transfer between the two gases.

[0058] In this embodiment, an optional additional flow of ambient gas 300 is accepted through the inlet aperture 350 and directed along channel 225 in order to cool the rear portion of the image assembly 80 (possibly a backlight). This embodiment uses a set of ribs 18, similar to the designs shown above in Figures 7 and 8. This embodiment also uses a thermally-conductive plate 10, similar to the one shown in Figure 7.
When this optional additional flow of ambient gas 300 is used, it is preferable that the anterior (front) surface 500 of the channel 225 be thermally conductive and preferably in thermal communication with at least a portion (preferably the rear portion) of the image assembly 80. Inlet aperture 350 may accept both ambient gas 310 and 300, or there may be separate inlet apertures for each flow of gas 310 and 300.

[0059] Similar to some of the previously described embodiments, the circulating gas 400 also passes over electronic assemblies in order to accept heat from these electronic assemblies. In this exemplary embodiment, the electronic assemblies have been separated by the heat exchanger 201 into two groups. The first group of electronic assemblies 900 may be considered the high power assemblies and may include but are not limited to: power modules, inductors, transformers, and other power-related devices. The second group of electronic assemblies 910 may be considered the low power assemblies and may include but are not limited to: timing and control boards, hard drives and other storage devices, video cards, software drivers, microprocessors, and other control devices. It is known to those skilled in the art that some high power electronic assemblies can cause electrical interference with other electronic assemblies that may be sensitive to electrical interference. Thus, in the exemplary embodiment shown, the heat exchanger 201 is used to separate the lower power electronic assemblies 910 from the high power electronic assemblies 900 to ensure a minimum amount of interference between the two. Further, some high power electronic assemblies 900 are known to also generate heat. This heat may be transferred to the circulating gas 400 prior to introducing this gas into the heat exchanger 201. In the exemplary embodiment shown, ambient air can be ingested as the ambient gas 310 and there is little risk of damage to the electrical assemblies 910 and 900 because the ambient gas 310 would preferably never contact these electrical assemblies. However, the electrical assemblies 910 and 900 will remain cool (as well as clean and dry) because of the cross-flow from the circulating gas 400.

[0060] The cooling system described herein may run continuously. However, if desired, temperature sensing devices (not shown) may be incorporated within the electronic display to detect when temperatures have reached a predetermined threshold value. In such a case, the various cooling fans may be selectively engaged when the temperature in the display reaches a predetermined value.
Predetermined thresholds may be selected and the system may be configured to advantageously keep the display within an acceptable temperature range. Typical thermostat assemblies can be used to accomplish this task. Thermocouples may be used as the temperature sensing devices. The speed of the various fan assemblies can also be varied depending on the temperature within the display.

[0061] It should be particularly noted that the spirit and scope of the disclosed embodiments provides for the cooling of any type of electronic display. By way of example and not by way of limitation, embodiments may be used in conjunction with any of the following: LCD (all types), light emitting diode (LED), organic light emitting diode (OLED), field emitting display (FED), light emitting polymer (LEP), organic electro luminescence (OEL), plasma displays, and any other type of thin/flat panel display.
Furthermore, embodiments may be used with displays of other types including those not yet discovered. In particular, it is contemplated that the system may be well suited for use with large LED backlit, high definition (1080i or 1080p or greater) liquid crystal displays (LCD). While the embodiments described herein are well suited for outdoor environments, they may also be appropriate for indoor applications (e.g., factory/industrial environments, spas, locker rooms, kitchens, bathrooms) where thermal stability of the display may be at risk.

[0062] It should also be noted that the variety of cooling channels that are shown in the figures may be shown in a horizontal or vertical arrangement but it is clearly contemplated that this can be reversed or changed depending on the particular embodiment. Thus, the closed loop may run horizontally or vertically and in a clock-wise or counter-clockwise direction. Further, the open loop may also be horizontal or vertical and can run left to right, right to left, and top to bottom, or bottom to top.

[0063] Having shown and described preferred embodiments, those skilled in the art will realize that many variations and modifications may be made to affect the described invention and still be within the scope of the claimed invention.
Additionally, many of the elements indicated above may be altered or replaced by different elements which will provide the same result and fall within the spirit of the claimed invention. It is the intention, therefore, to limit the invention only as indicated by the scope of the claims.

Claims (15)

1. A cooling system for an electronic image assembly having a front and back portion, the system comprising:

a front display surface spaced apart from the front portion of the electronic image assembly;

a channel defined by the space between the front display surface and the front portion of the electronic image assembly;

a heat exchanger in gaseous communication with the channel, the heat exchanger having first and second gas pathways, where the first gas pathway is in gaseous communication with the channel;

a first fan assembly positioned so as to force circulating gas through the channel and the first gas pathway; and a second fan assembly positioned so as to force ambient gas through the second gas pathway.

2. The cooling system of claim 1 wherein:

the heat exchanger is a cross-flow heat exchanger.

3. The cooling system of claim 1 further comprising:

a plate spaced apart from the rear portion of the electronic image assembly;

a second channel defined by the space between the plate and the rear portion of the electronic image assembly; and wherein the second fan assembly is further positioned so as to force ambient gas through the second channel.

4. The cooling system of claim 3 further comprising:

a power module in electrical communication with the electronic image assembly;

and a heat sink in thermal communication with the power module and placed within the second channel.

5. The cooling system of any one of claims 3 or 4 further comprising:
a plurality of ribs placed within the second channel.

6. An electronic display assembly comprising:
an electronic image assembly;

an isolating structure space apart from the electronic image assembly;
a channel defined by the space between the isolating structure and the electronic image assembly;

a power module having electronic components on a first side and a heat sink on the second side, where the power module is attached to the isolating structure so that the heat sink is within the channel and the electronic components are outside the channel; and a fan positioned so as to draw ambient gas through the channel.

7. The electronic display assembly of claim 6 further comprising:

a rib placed within the channel and in thermal communication with the isolating structure.

8. The electronic display assembly of claim 7 further comprising:

a surface placed within the channel and in thermal communication with the electronic image assembly and the rib;

9. The electronic display assembly of any one of claims 6, 7, or 8 wherein:
the electronic image assembly is a liquid crystal display.

10. The electronic display assembly of any one of claims 6, 7, or 8 wherein:
the electronic image assembly is an OLED display.

11. An electronic display assembly comprising:

an electronic image assembly having a front and rear portion;

a surface on the rear portion of the electronic image assembly and in thermal communication with the electronic image assembly;

a plate spaced apart from the surface;

a first channel defined by the space between the plate and the surface;

a power module in electrical communication with the electronic image assembly and in thermal communication with the plate; and a first fan positioned so as to draw ambient gas through the first channel.

12. The electronic display assembly of claim 11 further comprising:

a rib placed within the first channel and in thermal communication with the plate and the surface.

13. The electronic display assembly of claim 12 further comprising:

a front display surface spaced apart from the front portion of the electronic image assembly;

a second channel defined by the space between the front display surface and the front portion of the electronic image assembly;

a heat exchanger in gaseous communication with the second channel, the heat exchanger having first and second gas pathways, where the first gas pathway is in gaseous communication with the second channel;

a second fan positioned so as to force ambient gas through the second gas pathway; and a third fan positioned so as to force circulating gas through the second channel and the first gas pathway.

14. The electronic display assembly of any one of claims 11 through 13 wherein:
the electronic image assembly is a LCD.

15. The electronic display assembly of any one of claims 11 through 13 wherein:
the electronic image assembly is an OLED.