Patent Application
20130249374
1. Field of the Invention
The present invention relates generally to lamps or lighting fixtures, and more particularly to lamps and fixtures utilizing light emitting diodes (LEDs) and phase change heat radiators.
2. Description of the Related Art
Light emitting diodes (LED or LEDs) are solid state devices that convert electric energy to light and generally comprise an active region of semiconductor material sandwiched between two oppositely doped layers of semiconductor material. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED.
LEDs can be fabricated to emit light in various colors. However, conventional LEDs cannot generate white light from their active layers. Light from a blue emitting LED has been converted to white light by surrounding the LED with a yellow phosphor, polymer or dye, with a typical phosphor being cerium-doped yttrium aluminum garnet (Ce:YAG). The surrounding phosphor material “downconverts” the energy of some of the LED's blue light which increases the wavelength of the light, changing its color to yellow. Some of the blue light passes through the phosphor without being changed while a portion of the light is downconverted to yellow. The LED emits both blue and yellow light, which combine to provide a white light. In another approach light from a violet or ultraviolet emitting LED has been converted to white light by surrounding the LED with multicolor phosphors or dyes.
LEDs have certain characteristics that make them desirable for many lighting applications that were previously the realm of incandescent or fluorescent lights. Incandescent lights are very energy-inefficient light sources with approximately ninety percent of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs by a factor of about 10, but are still relatively inefficient. LEDs by contrast, can emit the same luminous flux as incandescent and fluorescent lights using a fraction of the energy.
In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000-20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of LEDs is attractive to many lighting suppliers and has resulted in their LED lights being used in place of conventional lighting in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications. An increase in the adoption of LEDs in place of incandescent or fluorescent lighting would result in increased lighting efficiency and significant energy saving.
LED based components or lamps have been developed that comprise an array of multiple LED packages mounted to a (PCB), substrate or submount. The array of LED packages can comprise groups of LED packages emitting different colors, and specular reflector systems to reflect light emitted by the LED chips. Some of these LED components are arranged to produce a white light combination of the light emitted by the different LED chips. Techniques for generating white light from a plurality of discrete light sources have been developed that utilize different hues from different discrete light sources, such as those described in U.S. Pat. No. 7,213,940, entitled “Lighting Device and Lighting Method”. These techniques mix the light from the discrete sources to provide white light.
In recent years, there have been dramatic improvements in light emitting diode technology such that LEDs of increased brightness and color fidelity have been introduced. Due to these improved LEDs, lighting modules have become available to further increase luminous flux output. Both single and multi-chip modules have become available, with a single-chip module generally comprising a single package with a single LED. Multi-chip lighting modules typically comprise a single package with a plurality of LEDs. These lighting modules, particularly the multi-chip modules, generally allow for high output of light emission, and are particularly useful in LED based lamps and fixtures.
LEDs emitting with high luminous flux can be driven with an elevated electrical drive signal, which in turn can cause the LEDs to operate at elevated temperatures. Operating at elevated temperatures can cause damage to the LEDs and/or their surrounding features, which can reduce their lifespan and reliability. There have been significant efforts directed to features or designs to manage the heat generated by the LED and that can draw heat away from the LEDs, causing the LEDs to operate at lower temperatures. Some of these designs include the use of passive heat radiators such as heat sinks that draw heat away from the LEDs and radiate the heat into the ambient. Heat sinks typically comprise a heat conducting material such as a metal, and some can include heat fins that increase the surface area of the heat sink to increase the amount of heat that transmits into the ambient. These types of heat sinks can be relatively large and bulky, and can result in a lamp that exceeds the desired geometric form factor for the lamp (e.g. standard A19 form factor). In addition, despite their large sizes, many passive heat sinks may not comply with the thermal requirement of the LED lamp or fixture.
Other heat management designs have been developed that utilize active cooling devices, such as fans, to radiate heat from the LEDs. Many of these designs utilize moving parts and can require electrical power to operate. This can result in an overall increase in power consumption for the lamp as well as potential failure of the moving parts.
The present invention is directed to phase change heat radiators that can be used in many different applications, but are particularly applicable to lamps or light fixtures (“lamp” or “lamps”) having solid state light sources such as LEDs. One embodiment of a lamp according to the present invention comprises one or more solid state light emitters and a radiator body with one or more coolant loops. A radiator fluid is included in the radiator body and coolant loops, with the solid state light emitters in thermal contact with the light emitters. Heat from the light emitters causes the radiator fluid to move through the radiator body and coolant loops to radiate heat from the solid state light emitters into the ambient.
Another embodiment of a lamp according to the present invention comprises one or more light emitting diodes (LEDs) and a phase change radiator in thermal contact with the LEDs. The radiator holds a phase change material capable of changing states in response to being heated from the LEDs, with the state change causing movement of the material away from the LEDs. As the material moves away heat from the material is radiated into the ambient. As this occurs the material can return to its cooled state. A path is included for returning the material into thermal contact with the LEDs.
Still another embodiment of a lamp according to the present invention comprise one or more solid state light emitters and a phase change radiator having a radiator fluid. The one or more solid state light emitters are in thermal contact with the radiator fluid, with heat from the light emitters heating a portion of the radiator fluid. The heated fluid then circulates away from the light emitters to radiate heat into the ambient.
These and other further features and advantages of the invention would be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings, in which:
The present invention provides heat management devices and structures that can be used in lamps and fixtures (“lamps”) having solid state light sources, such as one or more LEDs. Some lamp embodiments according to the present invention comprise one or more phase change radiators that utilize the latent heat of fluids to circulate and draw heat away from the LEDs and radiate the heat into the ambient, allowing for the LEDs to operate at a lower temperature. Latent heat is the heat energy required to change a fluid's liquid state to a gas state, and during this phase change state, the temperature does not change. Some phase change radiators according to the present invention can comprise a main radiator body and multiple radiator coolant loops mounted to the body. The present invention relies on the circulation of the “hot” fluid and gas utilizing the pressure differential between the two states. The process converts the LED heat loss energy to the fluid latent heat energy and fluid kinetic energy.
The different embodiments of the phase change radiators according to the present invention can also be constructed using simple and cost effective processes. The main radiator body can be fabricated from a main tubular pipe made of a metal such as copper or other brazable metals or combinations of metals. The radiator coolant loops constructed from smaller pipes made of the same or similar materials as the radiator body and can be pressed and mounted into holes in the radiator body. In still other embodiments, the coolant loops can be cast as one or more radiator banks that can then be attached to the radiator body.
End caps can be mounted over the openings in the end of the radiator body, and one end cap can comprise an LED printed circuit board (PCB). The opposite end cap can comprise a flat plate, with some embodiments having a metallic end plate with a copper-clad surface. In some embodiments, the LED PCB can comprise a metal core PCB such as an aluminum metal core LED PCB with a copper clad surface, and the other end cap can comprise aluminum covered with a copper clad surface. The end caps can be mounted in place using different methods, such as brazing.
The circulation loops can take many different shapes, with the circulation loops shown being U-shaped. The different shapes can be used to maximize surface area, and the loops can travel into any surrounding surface that can assist in radiating heat away from the lamp or fixture. Conventional heat sinks are fabricated by extruding which can have limitations regarding shape of features but the geometric features of the radiator are not constrained by the limitation of extruding. Different embodiments can also have heat fins or panels mounted on the coolant loops to further cool the liquid in the loops. In other embodiment the panels can be at least partially hollow to allow liquid from the coolant loops to enter to further dissipate the heat.
One or more coolant fluids can be included in the phase change radiators according to the present invention, with the coolant fluids being devised and selected for the desired boiling point and desirable working properties. In some embodiments, a “low” boiling point fluid is desired to provide for improved thermal management. Water boils at 100° C. at one atmosphere of pressure. At lower pressure water boils at lower temperatures, such at 80° C., and in vacuum, water can boil at a temperature in the range of 45 to 50° C. With a lower boiling temperature, the liquid within the phase change radiator changes states at a lower temperature, allowing the phase change radiator to conduct heat away from the LEDs at a lower temperature. This can allow improved management of the heat produced by the LEDs, allowing them to operate at lower temperatures. Accordingly, reducing the pressure in the phase change radiators according to the present invention can allow for regulating at lower temperatures.
Other fluids can also have lower boiling temperatures, such as isopropanol which boils at lower temperatures than water at different atmospheric pressures. This material has the additional advantage of not corroding or degrading the metal of the radiator body and coolant loops, as may be the case with water. One disadvantage of these types of materials is that they can exhibit a relatively low flash point. In some embodiments it may be desirable to use a mixture of water and a material with a higher flash point. Mixing the materials can result in a material having a lower boiling temperature, lower flash point, and a material that exhibits a reduction in corrosion or degradation of metal.
In some embodiments, the pressure in the radiator body can be reduced by creating a vacuum in the body and then sealing the body to hold the vacuum. The phase change radiator can only partially be filled with the coolant fluid, leaving a vacuum space that allows a vacuum to be pulled in the radiator. Lowering the pressure in the radiator lowers the boiling point of the coolant fluid, and the vacuum space in the invention allows for adjustable “low” temperature boiling. Creating a vacuum can be accomplished using many different types of valves or other mechanisms that allow for air to be drawn out of the radiator body and then allowing for the valve to be closed to hold the vacuum. Many different valves can be used including Schrader or Presta valves, commonly used with tires, or valves similar to those used with basketballs and volleyballs. In other embodiments, an opening or tube can be have a flange or tube that can be crimped to hold a vacuum with some other embodiments being soldered following crimping to hold the vacuum.
The vacuum space can also allow for expansion of the cooling fluid as it is heated during operation. The heat from the LEDs can cause the fluid to heat and eventually boil, causing the coiling liquid to expand and the fluid level to rise. This allows for the fluid to reach the necessary level or volume within the phase change radiator to allow the fluid to flow efficiently through the coolant loops.
The present invention provides many advantages over conventional all metal cast heat sinks. The embodiments allow for lower operating LED junction temperature, which increases the lifespan of the LED and provides a higher light efficiency operating point (lower LED thermal roll-off efficiency). The different embodiments can provide for scalable thermal handling capacity in the same form factor configuration. The different embodiments can weigh less and are smaller than all metal heat sinks, and can allow for higher power handling capacity.
The present invention is described herein with reference to certain embodiments but it is understood that the invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In particular, the present invention is described below in regards to light emitting devices, packages, arrays and lamps having substrates coated by a reflective coating typically comprising a carrier material filled with scattering particles of a different refractive index. Reflective coatings are described in U.S. patent application Ser. No. 13/017,778, to Andrews, and U.S. patent application Ser. No. 12/757,179 to Yuan et al., both of which are incorporated herein by reference.
It will be understood that when an element is referred to as being “on”, “connected to”, “coupled to” or “in contact with” another element, it can be directly on, connected or coupled to, or in contact with the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to”, “directly coupled to” or “directly in contact with” another element, there are no intervening elements present. Likewise, when a first element is referred to as being “in electrical contact with” or “electrically coupled to” a second element, there is an electrical path that permits current flow between the first element and the second element. The electrical path may include capacitors, coupled inductors, and/or other elements that permit current flow even without direct contact between conductive elements.
Although the terms first, second, etc. may be used herein to describe various elements, components, regions, and/or sections, these elements, components, regions, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, or section from another element, component, region, or section. Thus, a first element, component, region, or section discussed below could be termed a second element, component, region, or section without departing from the teachings of the present invention.
Embodiments of the invention are described herein with reference to cross-sectional view illustrations that are schematic illustrations of embodiments of the invention. As such, the actual thickness of components can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances are expected. Embodiments of the invention should not be construed as limited to the particular shapes of the regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. A region illustrated or described as square or rectangular will typically have rounded or curved features due to normal manufacturing tolerances. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the invention.
As mentioned above, the array of LEDs 18 can comprise a plurality of LEDs and in some embodiments the array can comprise LEDs 22 emitting different colors of light that combine to produce the desired lamp emission. In some embodiments the LEDs can emit different colors that combine to produce a white light emission from the lamp 10. In one embodiment, a multicolor source is used to produce white light. Several colored light combinations will yield white light. For example, it is known in the art to combine light from a blue LED with wavelength-converted yellow (blue-shifted-yellow) light to yield white light with correlated color temperature (CCT) in the range between 5000K to 7000K (often designated as “cool white”). Both blue and BSY light can be generated with a blue emitter by surrounding the emitter with phosphors that can be optically responsive to the blue light. When excited, the phosphors emit yellow light which then combines with the blue light to make white. In this scheme, because the blue light is emitted in a narrow spectral range it is called saturated light. The BSY light is emitted in a much broader spectral range and, thus, is called unsaturated light.
Another example of generating white light with a multicolor source is combining the light from green and red LEDs. RGB schemes may also be used to generate various colors of light. In some applications, an amber emitter is added for an RGBA combination. The previous combinations are exemplary; it is understood that many different color combinations may be used in embodiments of the present invention. Several of these possible color combinations are discussed in detail in U.S. Pat. No. 7,213,940 to van de Ven et al., herein incorporated by reference. Many different commercially available LEDs can be used such as those commercially available from Cree, Inc. These can include, but not limited to Cree's XLamp® XP-E LEDs or XLamp® XP-G LEDs.
The LEDs 22 can be mounted on a printed circuit board (PCB) 24 that is capable of being mounted on the first end of the radiator body 14. In some embodiments the PCB 24 can be comprise a metal core PCB, such as a copper clad aluminum metal core PCB, that can be mounted to the radiator body 14 using known methods such as brazing. It is understood, that the LED PCB need not be mounted directly to the radiator body 14, but that intervening layers or materials can be used. The end plate can also comprise a metal, such as aluminum, that can be mounted to the second end of the radiator body, also by brazing.
The coolant loops 16 can also comprise metal pipes, but with a smaller diameter than the radiator body 14. The coolant loops 16 can be bent into their desired shape, such as U-shaped in the LED lamp 10, and then can be mounted over holes 26 in the radiator body 14. The loops can comprise different heat conductive materials, with a suitable material being copper that allows for the loops to be brazed in place over the radiator body holes, with an air and watertight seal. The radiator body holes 26 provide a passageway for gas or liquids within the phase change radiator 12 to move between the radiator body 14 and the conductive loops 16. This movement allows for heated gas or liquids to cool as it passes through the conductive loops.
Referring now to
The phase change radiator 12 can be partially filled with its radiator fluid 28, leaving space at the of the radiator body 14. This allows room for the radiator fluid to expand during operation, and provides a space for pulling a vacuum within the radiator body 14 to lower pressure within the radiator body 14 and to allow the radiator fluid to boil at a lower temperature. This allows for the phase change action within the phase change radiator to begin at a lower temperature, thereby keeping the LEDs cooler. A vacuum valve 30 can be included near the top of the radiator body, with the valve passing into the open space above the radiator fluid 28. A vacuum can be turned in the radiator body by evacuating air from within the body 14. Once the vacuum is created, the valve can be closed to hold the vacuum. In one embodiment the valve 30 can comprise a rubber vacuum valve that can be vulcanized once a vacuum is achieved to hold the vacuum. Many different valves can be used, including those mentioned above, and in other embodiments a vacuum can be created during manufacturing without the use of a valve.
The phase change radiator 12 can also comprise features for connecting to a source of electricity such as to different electrical receptacles. In some embodiments the phase change radiator 12 can comprise a feature of the type to fit in conventional electrical receptacles. For example, it can include a feature for mounting to a standard Edison socket, which can comprise a screw-threaded portion which can be screwed into an Edison socket. In other embodiments, it can include a standard plug and the electrical receptacle can be a standard outlet, or can comprise a GU24 base unit, or it can be a clip and the electrical receptacle can be a receptacle which receives and retains the clip (e.g., as used in many fluorescent lights). These are only a few of the options for heat sink structures and receptacles, and other arrangements can also be used that safely deliver electricity from the receptacle to the lamp 10.
The lamps according to the present invention can comprise a power supply or power conversion unit that can comprise a driver to allow the bulb to run from an AC line voltage/current and to provide light source dimming capabilities. In some embodiments, the power supply can be housed in or adjacent to a phase change radiator 12 and can comprise an offline constant-current LED driver using a non-isolated quasi-resonant flyback topology. The LED driver can fit within the lamp and in some embodiments can comprise a 25 cubic centimeter volume or less, while in other embodiments it can comprise approximately 22 cubic centimeter volume or less and still in other embodiments 20 cubic centimeters or less. In some embodiments the power supply can be non-dimmable but is low cost. It is understood that the power supply used can have different topology or geometry and can be dimmable as well. Embodiments having a dimmer can exhibit many different dimming characteristics such as phase cut dimmable down to 5% (both leading and trailing edge). In some dimming circuits according to the present invention, the dimming can be realized by decreasing the output current to the LEDs.
The power supply unit can comprise many different components arranged on printed circuit boards in many different ways. The power supply can operate from many different power sources and can exhibit may different operating characteristics. In some embodiments the power supply can be arranged to operate from a 120 volts alternating current (VAC) ±10% signal while providing a light source drive signal of greater than 200 milliamps (mA) and/or greater than 10 volts (V). In other embodiments the drive signal can be greater than 300 mA and/or greater than 15V. In some embodiments the drive signal can be approximately 400 mA and/or approximately 22V.
The power supply can also comprise components that allow it to operate with a relatively high level of efficiency. One measure of efficiency can be the percentage of input energy to the power supply that is actually output as light from the lamp light source. Much of the energy can be lost through the operation of the power supply. In some lamp embodiments, the power supply can operate such that more than 10% of the input energy to the power supply is radiated or output as light from the LEDs. In other embodiments more than 15% of the input energy is output as LED light. In still other embodiments, approximately 17.5% of input energy is output as LED light, and in others approximately 18% or greater input energy is output as LED light.
During operation of the lamp 10, an electrical signal is applied to the LED array 18, causing the LEDs 22 to emit light. As this occurs, the LEDs 22 begin to heat and the heat transfers through the metal core PCB 24, to the radiator fluid 28. As the fluid is heated it expands within the radiator body 14, and eventually reaches a boiling temperature, changing some of the fluid to gas. This causes the heated fluids and gas to rise and shown by first arrows 32 in
One lamp embodiment was described with reference to
In this embodiment, radiator panels 62 can be mounted on the coolant loops 56 to increase the surface area for dissipating heat in the ambient. The radiator panels 62 can be made of many different thermally conductive materials, such as copper or aluminum and are mounted to and in thermal contact with the coolant loops 56 so that heat from the liquid in the coolant loops conducts into the radiator panels 62. The heat can then spread throughout the radiator panels 62 and into the ambient. This arrangement can increase the thermal handling capacity of the lamp 50 compared to lamps without radiator panels.
The radiator panels 62 can be arranged in many different ways and in the embodiment shown are in alignment with the radiator body 54. It is understood, that in other embodiments the radiator panels can be arranged in different ways and at different angles. For example, some or all of the radiator panels 62 can be orthogonal to the radiator body 54 or at various angles to the radiator body. The lamp 50 is shown with six radiator panels 62 on each coolant loop 56, but it is understood that more or fewer radiator panels can be included on each loop 56, and different ones of the loops can have different numbers of panels 62.
In lamp 50, the radiator panels can be solid and at least partially comprises a thermally conductive material. In other embodiments, the radiator panels 62 can be at least partially hollow. In still other embodiments, the panels 62 can be hollow and arranged so that liquid within the coolant loops 56 also runs through the radiator panels. In these embodiments, each of the coolant loops 56 can have openings on its first lateral section 64 and openings on its second lateral section. Each of the radiator panels can be arranged over an opening in the first lateral portion 64 and second lateral portion 66, so that liquid from the first lateral portion 64 enters the radiator panel's hollow portion. The liquid is then cooled through each radiator panel 62 and with the liquid traveling to the base of the radiator body 54 much in the same way that the cooling liquid in the radiator loops returns to the base of the radiator body 54. The liquid can then recirculate through the radiator body 54 to continue the cooling of the LED array.
Like the embodiments above, the LED lamp 50 can comprise a valve or other mechanism for allowing for the formation of a vacuum in the radiator body 54. In this embodiment, the mechanism comprises a valve (not shown), such as a rubber valve described above, located within a flange 68 (shown in
It is understood that different lamps according to the present invention can be arranged in many different ways beyond the embodiments shown above. Many different types of light sources can be used beyond the planar LED array shown above. In some embodiments the light source can comprise one or more LEDs mounted in a three-dimensional manner to achieve the desired emission characteristics.
The LEDs lamps can also be arranged with many additional elements to produce the desired color emission, and emission pattern.
As mentioned above, the different elements of the lamps according to the present invention can be arranged in many different ways beyond the embodiments described above. The elements can have many different shapes and sizes to provide the desired lamp emission thermal management characteristics.
While several illustrative embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. For example, many different radiator fluids in different combinations can be used beyond those described above. In some embodiments, a magnetized fluid can be used, and with these phase change radiators a magnet can be used to create a current in the phase change radiator to begin the cooling process. These embodiments can rely on one or both of the actions from the magnets and phase change to create the current to start the cooling process. In still other embodiments, the phase change radiator can take many different shapes and sizes beyond those described above, and the phase change radiators can be used in many different types of lamps and fixtures beyond those described above. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention as defined in the appended claims.
