Patent Grant
9593837
This invention relates to light fixtures and, more particularly, to LED light fixtures.
As a result of continuous technological advances that have brought about remarkable performance improvements, light-emitting diodes (LEDs) are increasingly finding applications in traffic lights, automobiles, general-purpose lighting, and liquid-crystal-display (LCD) backlighting. LED lighting is poised to replace existing lighting sources such as incandescent and fluorescent lamps since LEDs do not contain mercury, exhibit fast turn-on and dimmability, long life-time, and require low maintenance. Compared to fluorescent lamps, LEDs can be more easily dimmed either by linear dimming or PWM (pulse-width modulated) dimming. Indeed, lighting applications which previously had typically been served by fixtures using what are known as high-intensity discharge (HID) lamps are now being served by LED light fixtures.
LED light fixtures present problems which relate to size and configuration, ease of installation, servicing and configurational efficiency. Achieving improvements in such characteristics while also delivering excellent heat dissipation from light fixture components can be problematic. It is desired to achieve compactness in LED light fixtures, ease of installation and ease of servicing while still allowing excellent light output and operational efficiency.
The present disclosure relates to improved LED light fixtures. The LED light fixture may comprise a plurality of heat-sink-mounted LED-array modules, each module engaging an LED-adjacent surface of a heat-sink base for transfer of heat from the module. Heat-sink heat-dissipating surfaces may extend away from the modules. In some embodiments, the LED light fixture comprises at least one venting aperture through the heat-sink base to provide air ingress to the heat-dissipating surfaces adjacent to the aperture.
Additional embodiments of the present disclosure comprise circuits for balancing the current between two or more strings of LEDs in parallel or series. Embodiments may comprise a plurality of LED strings to form a light output, e.g., as a replacement for a traditional incandescent or florescent light source. In some embodiments, the voltage of each of the plurality of strings may be measured and compared, and based on the comparison; the current provided to each of the plurality of strings may be increased or decreased. In some embodiments, this may substantially balance the current between the strings. Alternatively, in some embodiments, the ratio between the current flowing through each of the plurality of strings may be set to a predetermined level to properly blend the brightness of each string. In some embodiments, this current balancing may be used for color or light output optimization.
Embodiments of the present disclosure may enable an LED to comprise advantageous light output characteristics. For example, in some embodiments, the cumulative light output of embodiments of the present disclosure may comprise an intensity of greater than or equal to 10,000 lumens. Further, in some embodiments, the cumulative light output may comprise a color temperature of greater than or equal to 4000° K. In some embodiments, the cumulative light output may comprise a Color Rendering Index (“CRI”) of at least 90. In some embodiments, the CRI may be 94 or greater. In some embodiments, the above characteristics may be achieved with a drive current of at least 700 mA. In some embodiments, the drive current may comprise 1,000 mA. In some embodiments, the cumulative light output comprises an intensity of greater than or equal to 13,000 lumens. In some embodiments, the chromaticity comprises within 0.2-0.225 u′ and 0.49-0.51 v′. Further in some embodiments, the total radiant flux is within the range of 30,900-41,600 mW.
Embodiments of the present disclosure may enable an LED to comprise advantageous light output characteristics. For example, in some embodiments, the cumulative light output of embodiments of the present disclosure may comprise an intensity of at least 10,000 lumens and a lumen efficiency of at least 100 lumens per watt. Further in some embodiments, the cumulative light output may comprise a color temperature of greater than or equal to 4000° K and a Color Rendering Index (“CRI”) of at least 70. In some embodiments, the cumulative light output comprising a color temperature of greater than or equal to 5000° K and a CRI of at least 90. In some embodiments, the drive current comprises at least 1000 mA and the cumulative light output comprises an intensity of greater than or equal to 13,000 lumens. In other embodiments, the cumulative light output comprises an intensity of greater than or equal to 25,000 lumens. In other embodiments, the LED light fixture is configured to operate based on a drive current comprises at least 700 mA and the cumulative light output comprises an intensity of greater than or equal to 20,000 lumens
In one embodiment, a system of the present disclosure may comprise: a light fixture comprising one or more LEDs configured to output a cumulative light output; wherein the cumulative light output comprises an intensity of greater than or equal to 10,000 lumens; and wherein the cumulative light output comprises a CRI of at least 90.
In another embodiment, a system of the present disclosure may comprise: a light fixture comprising one or more LEDs configured to output a cumulative light output at an efficiency; wherein the cumulative light output comprises at least 10,000 lumens; and wherein the efficiency comprises at least 100 lumens per watt.
These illustrative embodiments are mentioned not to limit or define the limits of the present subject matter, but to provide examples to aid understanding thereof. Illustrative embodiments are discussed in the Detailed Description, and further description is provided there. Advantages offered by various embodiments may be further understood by examining this specification and/or by practicing one or more embodiments of the claimed subject matter.
A full and enabling disclosure is set forth more particularly in the remainder of the specification. The specification makes reference to the following appended figures.
Reference will now be made in detail to various and alternative illustrative embodiments and to the accompanying drawings. Each example is provided by way of explanation, and not as a limitation. It will be apparent to those skilled in the art that modifications and variations can be made. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that this disclosure comprise modifications and variations as come within the scope of the appended claims and their equivalents.
One embodiment of the present disclosure comprises a plurality of LED strings used to form a light source, e.g., a replacement for a traditional incandescent bulb, florescent tube, compact florescent, or halogen bulb. Each LED string comprises one or more LEDs, and may comprise a plurality of LEDs in series. In some embodiments, the LEDs may all be of the same color, e.g., white, blue, red, etc. Alternatively, in some embodiments, one or more of the LEDs in a string may comprise a different color. Further, in some embodiments, each string of LEDs may be made up of different color LEDs.
In some embodiments, the LED light fixture may comprise a plurality of heat-sink-mounted LED-array modules, each module engaging an LED-adjacent surface of a heat-sink base for transfer of heat from the module. Heat-sink heat-dissipating surfaces may extend away from the modules. Further, in some embodiments, the LED light fixture comprises a plurality of heat sinks, each heat sink with its own heat-dissipating surfaces and heat-sink base. Each heat-sink base may have one of the LED-array modules engaged thereon. Further, the heat-sink base may be wider than the module such that the heat-sink base comprises a region beyond the module.
In some embodiments, the LED light fixture comprises at least one venting aperture through the heat-sink base to provide air ingress to the heat-dissipating surfaces adjacent to the aperture. The at least one venting aperture may comprise at least one venting aperture through the beyond-module portion of the heat-sink base. In some embodiments, the at least one venting aperture along the beyond-module portion of the heat-sink base comprises at least two venting apertures along the beyond-module portion. In some embodiments, the heat sinks may be made by extrusion.
In some embodiments, the LED light fixture comprises or is coupled to a mounting assembly that comprises a bar having a gripping region and a gripper grips the gripping region such that the light fixture is held with respect to the static structure. In some embodiments, the bar has a first end secured with respect to one or both of the static structures and a main body portion of the light fixture.
In some embodiments the mounting assembly is not adjustable. In such an embodiment, the bar may have a cross-sectional shape which is gripped by the gripper such that the fixture is held in one orientation. In such an embodiment, the cross-sectional shape of the bar may comprise rectangular shapes such as square. In other embodiments, the mounting assembly facilitates adjustment of the light fixture to a selected one of a plurality of possible orientations during installation. In some embodiments, the gripper grips the gripping region such that the light fixture is held in a selected one of the plurality of possible orientations.
In another embodiment of the present disclosure, the LED light fixture may comprise a circuit board comprising an LED-populated area (the circuit-board region within the closed boundary minimally circumscribing the LED light sources and a non-LED-populated area (the circuit-board region outside the LED-populated area). The LED light fixture may further comprise an optical aperture (the light-fixture opening of smallest cross-sectional area through which aperture the light from the LED-populated area passes). In some embodiments, the circuit board of the LED light fixture may comprise a substantially isothermal circuit board, in which temperature variation across the circuit board is no more than 5° C.
In some embodiments, at least 50% of the non-LED-populated area extends beyond the optical aperture. In some embodiments, substantially the entirety of the non-LED-populated area extends beyond the optical aperture. In some embodiments, at least 50% of the area of the circuit board extends beyond the optical aperture. The non-LED-populated area of the circuit board may extend beyond the optical aperture by, e.g., more than 0.5 inches on every side of the circuit board, or in some cases by at least about 1.0 inch on every side there-around. In some embodiments, the non-LED-populated area of the circuit board is greater than the LED-populated area.
As mentioned above, in some embodiments, during operation, the circuit board is substantially isothermal. In such an embodiment, the circuit board's non-LED-populated area extending beyond the optical aperture is very close in temperature to the temperature of its LED-populated area, and this facilitates heat dissipation. That is, the circuit board, which comprises a good thermally-conductive material, such as copper or aluminum, spreads the heat laterally away from the LED-populated area and allows rapid heat transfer to the heat-sink body from across the entire circuit board—even in such “hidden” positions as are beyond the boundary of the optical aperture. In some embodiments, the circuit board can be proximate heat-dissipating surfaces of the heat sink to provide a better thermal path to the heat dissipating surfaces of the heat sink. Embodiments of the present disclosure take advantage of the anisotropic nature of heat conduction—the fact that heat conduction laterally within the circuit board is greater than heat conduction from the circuit board to the heat-sink body. As such, the heat will tend to spread laterally away from the LED-populated area thus facilitating removal of heat from the LED-populated area to the non-LED-populated area and to the heat sink, which increases the optical efficiency of the LEDs. The spacing between adjacent LED light sources of the LED-populated area may be no more than about the cross-dimension of each of the LED light sources.
In some embodiments, the heat-sink body forms a base of the fixture. Some embodiments comprise a cover secured with respect to the base, the cover defining a light-transmissive opening over the LED-populated area.
In some embodiments, the opening in the cover defines the optical aperture. In other embodiments, a reflector or other optical element or lens defines the optical aperture. Depending on the embodiment, the optical elements defining the optical aperture can be integral with or mounted to the cover and/or LED assembly. In some embodiments, the aperture member is a reflector which extends from a first end adjacent to and surrounding the LED-populated area to a second end which is substantially aligned with the cover opening. The reflector enhances light output. In some embodiments, the LED-populated area is substantially rectangular in shape and the reflector is frusto-pyramidal in shape. Other embodiments are possible where the LED populated area is circular or rectangular and comprises an open space for mounting or electrical connections. In other embodiments, the cover serves as the aperture member and the light-transmissive opening is the optical aperture.
In some embodiments, a light-transmissive member is positioned in the cover opening. The light-transmissive member may comprise a phosphorescent material such that at least some of the light emitted by the fixture has a different wavelength than light as first emitted from the LED-populated area. For example the LEDs can be blue LEDs where the blue light excites the phosphorescent material, such as yttrium aluminum garnet (“YAG”), to produce a secondary emission of light where the blue light and the secondary emission produce white light. In other embodiments, different color LEDs can be used together with individual white LEDs (blue LEDs plus phosphor) or with blue LEDs in a remote phosphor configuration where the light-transmissive element is coated and/or impregnated with the phosphorescent material.
In some embodiments, the LED light fixture according to the present disclosure may comprise a low-profile LED light fixture. In such an embodiment, the low-profile LED light fixture comprises a base plate, an LED circuit board secured to a front surface of the base plate and at least one LED power-circuitry unit secured with respect to the front surface of the base plate in a position adjacent to the circuit board. In some embodiments, heat-dissipating surfaces extend from the front surface of the base plate, the LED circuit board being in position adjacent to the heat-dissipating surfaces. In some embodiments, the base plate has a substantially planar back surface from which no portion of the light fixture extends other than parts necessary for electrical connection, e.g., for surface mounting on a gasoline-station canopy.
In some embodiments, the heat-dissipating surfaces extend substantially orthogonally from the front surface of the base plate, and in some embodiments a cover is movably secured with respect to the base plate. Such cover may extend over the LED power-circuitry unit(s) while leaving uncovered the heat-dissipating surfaces and defining the aforementioned light-emitting opening over the LED circuit board.
In some embodiments, the base plate defines a pair of cavities along the front surface thereof, one on either side of the LED circuit board in positions along the other two opposite lateral sides of the base plate. Depending on the embodiment, the LED power-circuitry unit may be positioned within one of the two cavities. In some embodiments, light-fixture control circuitry, sensor and/or communication circuitry may be positioned within the other of the two cavities. Depending on the embodiment, a cover can extend over one or both cavities. In some embodiments, the light-emitting opening in the cover is bounded by portions of the cover over the LED power-circuitry and the control circuitry.
In some embodiments, the cross-section of the fixture in a plane orthogonal to the base plate and located between the back surface of the base plate and a forwardmost surface of the cover is such that the aspect ratio of such cross-section is greater than about 6:1. The aspect ratio may be greater than about 7.5:1. In some embodiments, the thickness of the cross-section is no more than about 3 inches, and may be no more than about 2 inches for a fixture of very low profile.
In some embodiments, the LED power-circuitry unit is in thermal communication with the cover, such that during operation primary heat transfer from the power-circuitry unit(s) is to the cover and primary heat transfer from the LED circuit board is to the base plate. In some embodiments, the power-circuitry unit may be directionally biased toward the cover to facilitate thermal contact between the power-circuitry unit and the cover.
The low-profile LED light fixture of the present disclosure may be a surface-mount fixture for mounting on a surface of a structure such that, when the fixture is installed, the back surface of the base plate is substantially against the structure surface—with no portion of the light fixture other than parts necessary for electrical connection being behind the structure surface. This allows mounting to gasoline-station canopies and the like with a minimal-size opening in the canopy. Such surface mounting also facilitates any needed servicing of such canopy light fixture.
In one embodiment, in order to increase the total number of LEDs in the light source, each of the plurality of strings of LEDs is placed in parallel. As is known in the art, the current flowing through two circuits in parallel is the input current multiplied by the ratio of the impedance of each circuit to the total impedance of the circuit. Thus, in the some embodiments, the current flowing through each of the strings of LEDs may be different. Thus, each string may have a different brightness. The present disclosure describes in detail multiple example circuits that solve this problem by controlling the current flowing through each string of LEDs. Controlling the current between each string of LEDs may guarantee a uniform brightness between each string. Further, controlling the current may enable higher quality light by controlling the current flowing through various color strings, for example, to set a level of warmth of the overall light output.
One system for solving this problem comprises placing two transistors, such as JFETs, with a common base in series with the two strings of LEDs and two current sensing resistors (one resistor associated with each string of LEDs). In such an embodiment, the common base may be connected to the collector of one of the transistors. In such an embodiment, if the two transistors are ideally matching, the voltages across the two current sensing resistors will be equal. Thus, the current shared by the two LED strings will be the ratio of the two sensing resistors. Thus, in an embodiment with two LED strings LED1 and LED2 and two resistors R1 and R2, the current across each LED string will be:
ILED1=I*R2/(R1+R2)
ILED2=I*R1/(R1+R2)
One drawback for a current sharing circuit according to this embodiment is that the voltage of the first string of LEDs (VLED1) needs to be no less than the string voltage of the second string of LEDS (VLED2). If this is not the case, then one of the transistors may enter saturation. When in saturation, the transistors may not control the current flowing through each string to the level set by the resistors, i.e., the current flowing through each string of LEDs may be different than the levels determined using the formulas above.
Another embodiment may comprise a third string of LEDs with a transistor connected in series with the third string and a common base with the other two transistors. Such an embodiment may further comprise a third sensing resistor in series with the third string of LEDs. In such an embodiment, the string voltage of the first string of LEDs (the string for which the transistor's base is connected to the collector) needs to be the highest among all the LED string voltages to ensure all the LED currents match the values set by the current sensing resistors.
In the embodiments described above, the constraint of maintaining the voltage drop across the first string of LEDs higher than the voltage drop across the other strings complicates the selection of LEDs. For example, the forward voltage drops of LED strings may vary with temperature and driving current. Thus, in one embodiment, desired operation may be ensured by selecting LEDs such that the minimum voltage of the first string of LEDs is no less than the maximum voltage of the other strings of LEDs. However, in some embodiments, this may increase power loss for the circuit. For example, in one embodiment, in a lighting fixture, if the voltage difference between the voltage of LED1 and the voltage of the other strings is 10V and the driving current is 0.35 A, the power loss will be 3.5 W. This may decrease the overall efficiency of the lighting fixture and also increase the thermal stress to the transistor and LEDs, thus shortening the operational life of the device.
Another embodiment may comprise using linear regulators to regulate the current to all but one of the strings of LEDs. However, such an embodiment may again suffer from the same deficiencies as the circuit described above.
Yet another embodiment for solving the problem discussed above may comprise current balancing transformers to equalize currents flowing through each of the LED strings. In one such embodiment, a magnetic balancer may be used to balance the current flowing through three strings of LEDs. In such an embodiment, two transformers with an equal number of turns of their primary and secondary windings may be connected between the output rectifier and the filter capacitor in three isolated outputs of a switch-mode power supply. Further, in such an embodiment, the current feedback from one output is used to set and regulate the current of the corresponding LED string. The 1:1 turn ratio of the transformer windings maintains the current flowing through each winding of the transformer at substantially the same value provided that the magnetizing current of the transformer is small compared to the winding current.
A deficiency of this embodiment is that it requires a switch-mode power supply. Thus, such an embodiment cannot be used independently, and lacks the flexibility to operate with an arbitrary DC source, for example, a DC current source. Furthermore, the addition of transformers for magnetic balancing into a switch-mode power supply increases the complexity and cost of the circuit. Furthermore, in some embodiments, separate output circuits may be detrimental if a large number of parallel LED strings are required. Furthermore, such an embodiment lacks the capability to individually change or tune the current flowing through each LED string once the turns-ratio of the transformer has been set. Thus, such an embodiment may not be effective for color mixing or control.
Another system for compensating for this problem without the above discussed deficiencies comprises a current control device such as a JFET or MOSFET in series with each string of LEDs. In this, embodiment, each current control device is controlled by a control device, such as a comparator and/or op-amp circuit. Each control device measures the voltage drop before and/or after the current control device, and based on this measurement, varies the impedance of the current control device, e.g., by varying a voltage to the base of the JFET, to increase or decrease the current flowing through each LED string. In some embodiments, the current measurement and control devices may be able to substantially balance the current flowing through each LED string in order to cause each LED string to have substantially the same light output.
Some embodiments may comprise sensing resistors placed in series with each LED string after the control circuit. Choosing resistors with different values may vary the voltage drop measured by each measurement device. Appropriate selection of the value of these sensing resistors enables the designer to vary the brightness of each string of LEDs to provide the desired light output. For example, the designer may comprise multiple strings of white LEDs kept at a substantially high brightness, but further comprise one string of red LEDs to provide a warmer light output. In such an embodiment, the designer may select sensing resistors configured to cause the string of red LEDs to receive a lower current, and therefore be dimmer than the string of white LEDs. In such an embodiment, the brightness of the red LEDs may be set to provide the desired warmth of the total light output.
These illustrative embodiments are mentioned not to limit or define the limits of the present subject matter, but to provide examples to aid understanding thereof. Illustrative embodiments are discussed in the Detailed Description, and further description is provided there. Advantages offered by various embodiments may be further understood by examining this specification and/or by practicing one or more embodiments of the claimed subject matter.
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In some embodiments, configurations in which the light sources are in thermal communication with base 20 while power-circuitry unit 40 is in thermal communication with cover 30, may be advantageous. In such embodiments, during operation of the light fixtures this arrangement provides primary heat transfer from the power-circuitry unit and primary heat transfer from the LED emitter(s) to separate major enclosure members, each of which serves as a heat sink.
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The large non-LED-populated area surrounding the LED-populated area provides advantages, such as anisotropic heat conduction during operation. In particular, heat generated by the LED light sources on the LED-populated area spreads in lateral directions across the entire circuit board more than in directions orthogonal to the circuit board into the heat-sink body. That is, the circuit board, which comprises a good thermally-conductive material, such as copper or aluminum, spreads the heat laterally away from the LED-populated area and allows rapid heat transfer to the heat-sink body from across the entire circuit board—even in such “hidden” positions as are beyond the boundary of the optical aperture.
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The present disclosure provides efficient ways for addressing thermal challenges and extracting increased amounts of light from the LEDs of LED light fixtures. One such way, as described above, is increasing the surface area of the printed circuit board without changing the configuration of the LED array thereon. This takes advantage of the extra circuit-board material for heat-transfer purposes.
In some embodiments, the material used for the LED circuit board should be selected with particular regard to its thermal conductivity. In some embodiments, a simple metal-core circuit board is comprised of a solder mask, a copper circuit layer, a thermally-conducting thin dielectric layer, and a much thicker metal-core base layer. Such layers are laminated and bonded together, providing a path for heat dissipation from the LEDs. In some embodiments, the base layer is by far the thickest layer of the circuit board and may be aluminum, or in some cases copper, a copper alloy or another highly thermally-conductive alloy. A highly-conductive base layer facilitates lateral conduction of heat in the board from beneath the LED-populated area to and across the non-LED-populated area. And since board temperatures remain high even across the non-LED-populated area, the total area of substantial thermal transfer from the circuit board to the heat sink is beneficially large—substantially larger than just the LED-populated area.
In some embodiments, instead of sizing the circuit board to closely match the size of the LED array, the circuit board may be enlarged to have a non-LED-populated area around an LED-populated area such that the non-LED-populated area extends beyond the optical aperture. In one example, such circuit-board enlargement decreases the temperature of the LEDs by 2° C. without adding manufacturing costs allowing for an increase on total lumen output. Larger decrease in temperature and larger increase in total lumen output are possible depending on non-LED-populated area of such a circuit board.
The present disclosure provides a further way for addressing thermal challenges in LED light fixtures. In some embodiments, the thermal load of the driver (power-circuitry unit) is substantially removed from the fixture member (e.g., the base member), which is in primary thermal communication with the LED circuit board. In such an embodiment, the thermal load of the driver may instead be transferred to a separate fixture member such as the light-fixture cover. In one example, such thermal “repositioning” of the driver provides a decrease in the LED temperature of about 2° C. and the thermal separation of the driver from the LED circuit board also lowers the driver temp by 2° C. This permits drive current to be increased while still maintaining a 100,000 hour driver life rating and allowing an increase on total lumen output.
In some examples of light fixtures of this disclosure, enlargement of the non-LED-populated area is combined with separation of the primary thermal paths of the LEDs and the LED driver. In one example, this combination of thermal advantages decreases the LED temperature by 4° C. and allows a 15% increase in the drive current which resulted in 13% increase in total lumen output.
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In some embodiments, the heat-dissipating surfaces comprise the surfaces of edge-adjacent fins 621 extending transversely from beyond-module portion 681 of heat-sink base 68 at a position beyond venting apertures 69 therealong. As shown in
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In some embodiments, heat-sink base 68 comprises a module-engaging portion 685 between beyond-module portions 681. Heat-sink heat-dissipating surfaces comprise the surfaces of a plurality of middle fins 622 extending transversely from module-engaging portion 685 of heat-sink base 68, as shown in
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Additional examples of LED-array modules are disclosed in co-pending U.S. patent application Ser. No. 11/774,422, the contents of which are incorporated herein by reference. In fixtures utilizing a plurality of emitters, a plurality of LEDs or LED arrays may be disposed directly on a common submount in spaced relationship between the LEDs or LED arrays. These types of LED emitters are sometimes referred to as chip-on-board LEDs.
The above-described thermal management of the LED light fixture including venting gaps 18A, 18B and through heat sink venting apertures 69 allows maximization of the power density of LEDs on the printed circuit board. In some embodiments, this may be maximized to 4.9 W per square inch or greater. This is in contrast to prior fixtures, which may be limited to less than 3.2 W per square inch. In some embodiments, the LED junction temperature and resulting lifetime of the LEDs is improved even at the higher power density which results in a 50,000 hour lumen maintenance factor of a minimum of 86% at 15° C.
Furthermore, the thermal management of the LED light fixture allows each heat sink to function in thermal isolation from neighboring heat sinks which minimizes thermal compromise with increasing the number of heat sinks in the modular LED light fixture. In some embodiments, a number lumens delivered per unit area of the modular LED assembly (sometimes referred to as “light engine”) is increased from previously possible 95 lumens per square inch to over 162 lumens per square inch. This is allowed by the thermal management of the LED light fixture. This is in contrast with prior modular fixtures in which due to the thermal interference between adjacent heat sinks, an increase the number of light engine heat sinks resulted in a decrease in lumen flux to as low as 56 lumens per square inch.
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In some embodiments, light fixture 10 comprises a main body portion 20 and a mounting assembly 30 for adjustable securement to a static structure. An example static structure is shown in
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In some embodiments, bar-engaging surfaces 431 and 441 of gripper 40 and gripping region 32 of bar 31 are configured for a finite number of the orientations. As shown in
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The LED strings 104 and 106 comprise one or more LEDs, for example a plurality of LEDs in series. Each of LED strings 104 and 106 may comprise a plurality of inorganic LEDs, which may comprise semiconductor layers forming p-n junctions and/or organic LEDs (OLEDs), which may comprise organic light emission layers. In some embodiments, light perceived as white or near-white may be generated by a combination of red, green, and blue (“RGB”) LEDs. Output color of such a device may be altered by separately adjusting supply of current to the red, green, and blue LEDs.
The current control devices 108 and 110 comprise devices configured to control the current flow through each LED string 104 and 106. In some embodiments, current control devices 108 and 110 may comprise transistors such as a Bipolar Junction Transistor (BJT). In such an embodiment, the BJT may be configured to act as a switch to control current flow, e.g., by connecting the BJT in series with an LED string, such that current must flow from the collector to the emitter of the BJT. In such an embodiment, varying the current applied to the base of the BJT may vary the current allowed to flow through the BJT and thus the amount of current that is allowed to flow through the string of LEDs. In another embodiment, the current control devices 108 and 110 may comprise MOSFETs. In such an embodiment, the MOSFET may be configured to act as a switch to control current flow, e.g., by connecting the MOSFET in series with an LED string such that current must flow from the MOSFET's drain to its source. In such an embodiment, varying the voltage applied to the gate of the MOSFET may vary the current allowed to flow through the MOSFET and thus the amount of current that is allowed to flow through the string of LEDs. In some embodiments, because a MOSFET can be driven using voltage, a MOSFET will require lower power and thus use less energy and reduce the total heat dissipated by the circuit. In other embodiments, current control devices 108 and 110 may comprise other transistors, e.g., junction gate field-effect transistors (JFET) or insulated gate field effect transistors (IGFET).
The voltage measurement devices 112 and 114 comprise devices configured to measure the voltage drop at a point along each LED string. For example, in some embodiments a sensing resistor of a known value may be located either before or after each string of LEDs. By measuring the voltage drop across this resistor, the voltage measurement devices 112 and 114 may be able to determine the current flowing through each string of LEDs, e.g., because V=I*R. Further, in some embodiments, each current control device is configured to measure the voltage at each string of LEDs. In some embodiments, each voltage measurement device is configured to compare the voltage of each string of LEDs and, based on the comparison; output a current/voltage to current control devices 108 and 110. As described above, this current/voltage will cause current control devices 108 and 110 to vary the current allowed to pass through each LED string.
In some embodiments, each of voltage measurement devices 112 and 114 may comprise a circuit comprising both a comparator and an op-amp. As is known in the art, a comparator is a device that compares two voltages or currents and outputs a digital signal indicating which is larger. Ordinarily, a comparator will have two analog input terminals V+ and V−, and one binary digital output. The output of a comparator in ordinary operation is:
Output=high, if V+>V−
Output=low, V+<V−
Similarly, an op-amp can be configured to amplify the difference between two signals. In some embodiments, each of the comparator and the op-amp is configured to receive the voltage from each of the two LED strings. Further, each is configured to compare these voltages and output a signal indicating which voltage is higher.
In one embodiment, the comparator configured to control LED string 104 may receive the voltage associated with LED string 104 at its negative terminal and the voltage associated with LED string 106 at its positive terminal. In such an embodiment, if the voltage of LED string 104 is higher than the voltage of LED string 106, the comparator will set its output to high. Such a setting will cause the current control device 108 to increase current flow. Alternatively, if the voltage of LED string 104 is lower than the voltage of LED string 106, the comparator will set its output to low. Such a setting will cause the current control device 108 to reduce current flow.
In some embodiments, voltage measurement devices 112 and 114 may comprise op-amps configured to measure the voltage after each of current control devices 108 and 110. For example, in some embodiments, sensing resistors of a known value may be located after the output of current control devices 108 and 110. By measuring the voltage drop across these resistors, the op-amps may be able to make further determinations regarding the current flowing through each string of LEDs. For example, in the embodiment described above, wherein the voltage across LED string 104 is higher than the voltage across LED string 106, an op-amp associated with voltage measurement device 112 amplifies the difference, i.e., output=voltage of LED string 104—voltage of LED string 106. If the voltage of LED string 106 becomes lower, the op-amp will increase its output and thus provide a higher driving voltage/current to current control device 108, which increases the current flowing through LED string 104.
In some embodiments, voltage measurement devices 112 and 114 may comprise both op-amps and comparators. In other embodiments, voltage measurement devices 112 and 114 may each comprise only op-amps. An op-amp may be advantageous because generally they are of lower cost than a comparator. However, comparators may be advantageous due to a faster slew rate that can reduce noticeable oscillations in the current found on each string of LEDs.
Embodiments of the present disclosure may allow for current matching, i.e., causing both of LED strings 104 and 106 to have substantially the same current. Other embodiments are configured to allow for current tuning, i.e., causing LED strings 104 and 106 to each have a predetermined current or a predetermined relationship between currents, e.g., in one embodiment, LED string 104 will have 40% of the total current regardless of the total current. These design choices allow a designer to set the level of brightness between each string of LEDs, or the ratio of brightness between each string of LEDs.
Further, in some embodiments, different color strings of LEDs may be used. A designer may use embodiments of the present disclosure to tune the brightness of each string to provide the desired light output and color mixing. For example, the designer may comprise multiple strings of white LEDs kept at a substantially high brightness, but further comprise one string of red LEDs to provide a warmer light output. In such an embodiment, the designer may select sensing resistors configured to cause the string of red LEDs to receive a lower current, and therefore be dimmer than the strings of white LEDs. In such an embodiment, the brightness of the red LEDs may be set to provide the desired warmth of the total light output. Further, in some embodiments one or more the LED strings may comprise different color LEDs, or LEDs with different light output characteristics, e.g., dominant wavelength (“DW”), peak wavelength (“PW”), uniform light output, total luminous flux (“TLF”), and light color rendering index (“CRI”). Embodiments of the present disclosure may be used to control current flow through each string of LEDs to compensate for these factors.
In some embodiments, additional LED strings may be comprised. For example, in one embodiment, a third string of LEDs, a third current control device, and a third voltage measurement device may be comprised. In such an embodiment, the sensing resistors may be selected to provide for current matching between each of the three strings or for a predetermined ratio between the current of each of the three strings. In still other embodiments, additional LED strings, current control devices, and voltage measurement devices may be comprised. In still other embodiments, a plurality of circuits of the type described with regard to
In some embodiments, each of the components described with regard to
Turning now to
As shown in
As shown in
In another embodiment, if VS2 becomes higher, the output of op-amp 2 becomes lower, providing a lower driving current (Ibe2) to the bipolar transistor Q2 and the current flowing through the collector of Q2, i.e., the current of the second string of LEDs (ILED2) will decrease.
In the embodiment shown in
In another embodiment, V1 may be higher than V2 if VLED1 is lower than VLED2. In this case, the output of comparator 2 is set to high whereas the output of comparator 1 is set to low and bipolar transistor Q2 is saturated or fully turned on, while the current through the collector and emitter of bipolar transistor Q1 is controlled by the output of op-amp 1. In such an embodiment, op-amp 1 takes the sensed current signal VS2 as the current reference for string LED 1. In the same manner described above, the current ILED 1 flowing through LED 1 is regulated, and ILED1=ILED2*(R2/R1). Therefore, ILED2=ILED2 if R1=R2.
Thus, in the example described above, the comparator and op-amp circuits automatically differentiate which LED string has a higher voltage, and provide an exact current to the LED strings as set by the ratio of the two current sensing resistors R1 and R2.
A person of ordinary skill in the art will recognize that the circuit shown in
Turning now to
In system 300, shown in
A person of ordinary skill in the art will recognize that the circuit shown in
Turning now to
The PWM pulse can be a control signal from an external control unit or an on-board micro-controller. With this tuning circuit, the impedance of the control switch QT can be varied. For example, in the embodiment shown in
A person of ordinary skill in the art will recognize that the circuit shown in
Turning now to
In circuit 500, each component other than the three comparators operates in substantially the same way as described above with regard to
As shown in
ILED1=((R2*R3)/Δ)*I
ILED2=((R1*R3)/Δ)*I
ILED3=((R1*R2)/Δ)*I
One of ordinary skill in the art will recognize that if R1=R2=R3, then ILED1=ILED2=ILED3. Thus, by setting each resistor to an equal value, each LED string may have substantially the same brightness. Alternatively, the resistor values may be varied in order to vary the brightness of each string. In some embodiments, this may be employed for color or lighting compensation. For example, in some embodiments, one or more of the LED strings may comprise different color LEDs, or LEDs with different light output characteristics, e.g., dominant wavelength (“DW”), peak wavelength (“PW”), uniform light output, total luminous flux (“TLF”), and light color rendering index (“CRI”). In some embodiments a designer may select values of resistors R1, R2, and R3 in order to compensate for these differences or provide a higher overall light quality. For example, in one embodiment, one of the LED strings may comprise LEDs of a different color than the other two strings. In such an embodiment, resistors R1, R2, and R3 may be selected such that this different color string has a different current level and thus a different brightness than the other two strings. This may be used to, for example, change the warmth of the light output or control the color of the light.
A person of ordinary skill in the art will recognize that the circuit shown in
Turning now to
In some embodiments, the designer may set the value of resistors R1 and R2 to set a balance between the current through LED strings LED1 and LED2. This will also set the brightness of each of these strings. A designer may set this brightness in order to compensate for color or other factors associated with the LEDs in each string.
Further, in the embodiment shown in
A person of ordinary skill in the art will recognize that the circuit shown in
Turning now to
Each module shown in
Further, in some embodiments, other types of current balancing circuits, such as those described throughout this application may be comprised in a module form. Further, in some embodiments, a plurality of modules such as those shown in
A person of ordinary skill in the art will recognize that the circuit shown in
Turning now to
In the embodiment shown in
In some embodiments, a benefit of using a switching regulator may be lower power loss. In some embodiments, this can improve the overall efficiency of the circuit, and reduce the amount of heat generated by the power loss. In some embodiments, this advantage may still be present even if the voltage difference between LED1 and LED2 is relatively high.
A person of ordinary skill in the art will recognize that the circuit shown in
Turning now to
In the embodiment shown in
In the embodiment shown in
A person of ordinary skill in the art will recognize that the circuit shown in
Turning now to
A person of ordinary skill in the art will recognize that the circuit shown in
There are numerous advantages of the current sharing circuit of present disclosure.
The present disclosure provides efficient ways for addressing thermal challenges and extracting increased amounts of light from the LEDs of LED light fixtures. One such way, as described above, is increasing the surface area of the printed circuit board without changing the configuration of the LED array thereon. This takes advantage of the extra circuit-board material for heat-transfer purposes.
In some embodiments, the disclosed low-profile configuration of the light fixture permits installation against the structure with a relatively small aperture formed in structure surface 1 for electrical connections. This is beneficial in installations for outdoor canopies such as those used at gasoline stations. In particular, the small connection aperture minimizes access of water to the fixture. Another benefit provided by the light fixture according to the present disclosure is that all major components are accessible for servicing from the light-emitting front of the fixture, under the canopy.
Further, some embodiments of the present disclosure provide more flexibility when choosing LED strings. For example, embodiments of the present disclosure enable the designer to select different LEDs with different characteristics. In some embodiments, this enables the designer to comprise different numbers of LEDs in each string.
Further, embodiments of the present disclosure enable additional LED strings to be placed in the same package. Because these LED strings can be placed in parallel, the total voltage drop of the circuit can be reduced. This can allow the designer to build an LED circuit with a greater number of LEDs, and therefore a higher overall light output. Furthermore, as discussed above, an even larger number of LEDs may be incorporated by using a modular approach with a plurality of current sharing drivers of the types discussed above.
Embodiments described above also allow the designer to adjust brightness to create a more pleasing (e.g., warmer light) or to compensate for other factors associated with the each LED, string of LEDs, or module of LEDs. For example, in some embodiments the resistors may be selected to compensate for different light output characteristics, e.g., dominant wavelength (“DW”), peak wavelength (“PW”), uniform light output, total luminous flux (“TLF”), and light color rendering index (“CRI”). In some embodiments, this enables a broader range of LEDs to be used, reducing production cost, because marginal LEDs that would previously have been discarded may be used. Further, the current level can be set to maximize the life of each LED or string of LEDs.
Embodiments of the present disclosure may enable an LED to comprise advantageous light output characteristics. For example, in some embodiments, the cumulative light output of embodiments of the present disclosure may comprise an intensity of greater than or equal to 10,000 lumens. Further, in some embodiments, the cumulative light output may comprise a color temperature of greater than or equal to 4000° K. In some embodiments, the cumulative light output may comprise a Color Rendering Index (“CRI”) of at least 90. In some embodiments, the CRI may be 94 or greater. In some embodiments, the above characteristics may be achieved with a drive current of at least 700 mA. In some embodiments, the drive current may comprise 1,000 mA. In some embodiments, the cumulative light output comprises an intensity of greater than or equal to 13,000 lumens. In some embodiments, the chromaticity comprises within 0.2-0.225 u′ and 0.49-0.51 v′. Further in some embodiments, the total radiant flux is within the range of 30,900-41,600 mW.
Further, embodiments of the present disclosure may enable higher efficiency light, for example, in some embodiments the lumen efficiency may comprise at least 98 lumens per Watt. In some embodiments, the lumen efficiency may comprise at least 105 lumens per Watt.
The table below shows non-limiting example characteristics of LED lighting fixtures according to the embodiments disclosed herein.
Embodiments of the present disclosure may enable an LED to comprise advantageous light output characteristics. For example, in some embodiments, the cumulative light output of embodiments of the present disclosure may comprise an intensity of at least 10,000 lumens and a lumen efficiency of at least 100 lumens per watt. Further in some embodiments, the cumulative light output may comprise a color temperature of greater than or equal to 4000° K and a Color Rendering Index (“CRI”) of at least 70. In some embodiments, the cumulative light output comprises a color temperature of greater than or equal to 5000° K and a CRI of at least 90. In some embodiments, the drive current comprises at least 1000 mA and the cumulative light output comprises an intensity of greater than or equal to 13,000 lumens. In other embodiments, the cumulative light output comprises an intensity of greater than or equal to 25,000 lumens. In other embodiments, the LED light fixture is configured to operate based on a drive current comprising at least 700 mA and the cumulative light output comprises an intensity of greater than or equal to 20,000 lumens
The table below shows non-limiting example characteristics of LED lighting fixtures according to the embodiments disclosed herein, in which the light temperature comprises at least 4000° K and the Color Rendering Index (“CRI”) comprises at least 70.
The table below shows non-limiting example characteristics of LED lighting fixtures according to the embodiments disclosed herein, in which the light temperature comprises at least 5700° K and the CRI comprises at least 70.
The table below shows non-limiting example characteristics of LED lighting fixtures according to the embodiments disclosed herein, in which the light temperature comprises at least 5000° K and the CRI comprises at least 90.
The methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For instance, in alternative configurations, the methods may be performed in an order different from that described, and/or various stages may be added, omitted, and/or combined. Also, features described with respect to certain configurations may be combined in various other configurations. Different aspects and elements of the configurations may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples and do not limit the scope of the disclosure or claims.
Specific details are given in the description to provide a thorough understanding of example configurations (including implementations). However, configurations may be practiced without these specific details. For example, well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the configurations. This description provides example configurations only, and does not limit the scope, applicability, or configurations of the claims. Rather, the preceding description of the configurations will provide those skilled in the art with an enabling description for implementing described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure.
Having described several example configurations, various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. For example, the above elements may be components of a larger system, wherein other rules may take precedence over or otherwise modify the application of the invention. Also, a number of steps may be undertaken before, during, or after the above elements are considered. Accordingly, the above description does not bound the scope of the claims.
The use of “adapted to” or “configured to” herein is meant as open and inclusive language that does not foreclose devices adapted to or configured to perform additional tasks or steps. Additionally, the use of “based on” is meant to be open and inclusive, in that a process, step, calculation, or other action “based on” one or more recited conditions or values may, in practice, be based on additional conditions or values beyond those recited. Headings, lists, and numbering comprised herein are for ease of explanation only and are not meant to be limiting.
Embodiments in accordance with aspects of the present subject matter can be implemented in digital electronic circuitry, in computer hardware, firmware, software, or in combinations of the preceding. In one embodiment, a computer may comprise a processor or processors. The processor comprises or has access to a computer-readable medium, such as a random access memory (RAM) coupled to the processor. The processor executes computer-executable program instructions stored in memory, such as executing one or more computer programs including a sensor sampling routine, selection routines, and other routines to perform the methods described above.
While the present subject matter has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, it should be understood that the present disclosure has been presented for purposes of example rather than limitation, and does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.
As used herein in referring to portions of the devices of this disclosure, the terms “upward,” “upwardly,” “upper,” “downward,” “downwardly,” “lower,” “upper,” “top,” “bottom” and other like terms assume that the light fixture is in its usual position of use and do not limit the invention to any particular orientation.
In descriptions of this disclosure, including in the claims below, the terms “comprising,” “including” and “having” (each in their various forms) and the term “with” are each to be understood as being open-ended, rather than limiting, terms.
The present application claims priority to, and is a continuation-in-part of U.S. patent application Ser. No. 14/083,070 filed on Nov. 18, 2013, and entitled “Systems and Methods for a Current Sharing Driver for Light Emitting Diodes.” The present application also claims priority to, and is a continuation-in-part of U.S. patent application Ser. No. 13/787,579 filed on Mar. 6, 2013, and entitled “Led Light Fixture.” The present application also claims priority to, and is a continuation-in-part of U.S. patent application Ser. No. 13/839,922 filed on Mar. 15, 2013, and entitled “High-Output LED Light Fixture” which claims priority to U.S. Provisional Application Ser. No. 61/624,211, filed Apr. 13, 2012 and is a continuation-in-part of patent application Ser. No. 13/333,198, filed Dec. 21, 2011, now U.S. Pat. No. 8,313,222, issued Nov. 20, 2012, which is a continuation of patent application Ser. No. 12/418,364, filed Apr. 3, 2009, now U.S. Pat. No. 8,092,049, issued Jan. 10, 2012, which claims priority to U.S. Provisional Application Ser. No. 61/042,690, filed Apr. 4, 2008. The entirety of all of the aforementioned applications are incorporated by reference herein.
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| 20140247590 A1 | Sep 2014 | US |
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| Number | Date | Country | |
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| Parent | 12418364 | Apr 2009 | US |
| Child | 13333198 | US |
| Number | Date | Country | |
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| Parent | 14083070 | Nov 2013 | US |
| Child | 14188184 | US | |
| Parent | 13787579 | Mar 2013 | US |
| Child | 14083070 | US | |
| Parent | 13839922 | Mar 2013 | US |
| Child | 13787579 | US | |
| Parent | 13333198 | Dec 2011 | US |
| Child | 13839922 | US |
