LED fixture with integrated driver circuitry

Abstract

A solid state lighting fixture with an integrated driver circuit. A housing has a base end and an open end through which light is emitted from the fixture. The reflective interior surface of the fixture and the base define an optical chamber. At least one, and often multiple, light sources are mounted at the fixture base along with the circuitry necessary to drive and/or control the light sources. The drive circuit and the light sources are both located in the optical chamber. A reflective cone fits within the optical chamber such that it covers most of the drive circuit and other components at the base of fixture that might absorb light. The reflective cone is shaped to define a hole that is aligned with the light sources so that light may be emitted through the hole toward the open end of the fixture.

Claims

1. A solid state light fixture, comprising: a solid state lighting housing comprising a base and an interior reflective surface that define an optical chamber with an open end; a plurality of light emitting diodes within said optical chamber; a driver circuit within said optical chamber; a junction box on said housing; and at least one mounting mechanism operable to releasably mount said fixture in an opening in a ceiling, wherein said mounting mechanism is attached to said fixture between said housing and said junction box; and wherein said interior reflective surface is positioned to redirect light from said plurality of light emitting diodes out of said open end.

2. The light fixture of claim 1, wherein said open end is against the ceiling around said ceiling opening.

3. The light fixture of claim 2, wherein said mounting mechanism urges the housing open end against the ceiling around said ceiling opening.

4. The light fixture of claim 2, wherein said ceiling is between said mounting mechanism and said housing open end.

5. The light fixture of claim 1, wherein said housing protrudes through said ceiling opening and into a plenum.

6. The light fixture of claim 1, wherein said mounting mechanism comprises one or more springs.

7. The light fixture of claim 1, wherein said mounting mechanism comprises one or more spring clips.

8. The light fixture of claim 1, wherein said fixture is mounted directly to said ceiling.

9. The light fixture of claim 1, said junction box detachably mounted to said housing.

10. The light fixture of claim 9, wherein said junction box is mounted to said ceiling with said housing removably attached to said junction box.

11. A ceiling lighting system, comprising: a ceiling defining a ceiling opening; and a solid state light fixture in said ceiling opening, said fixture comprising: a housing protruding though said ceiling opening and into a plenum, said housing comprising a base, a reflective interior surface, and an open end opposite said base, said reflective interior surface extending from said base to said open end; a light emitting diode within said housing; a driver circuit within said housing; a junction box on said housing; and a mounting mechanism operable to removably mount said fixture in said ceiling opening with said housing opening positioned against the ceiling around the ceiling opening, wherein said mounting mechanism is between said housing and said junction box; and wherein said reflective interior surface redirects light from said light emitting diode out of said open end.

12. The ceiling lighting system of claim 11, wherein said mounting mechanism urges the housing opening against the ceiling around said ceiling opening.

13. The ceiling lighting system of claim 11, wherein said ceiling is between said mounting mechanism and said housing open end.

14. The ceiling lighting system of claim 11, wherein said mounting mechanism comprises springs or spring clips.

15. The ceiling lighting system of claim 11, wherein said fixture is mounted directly to said ceiling.

16. The ceiling lighting system of claim 11, said junction box detachably mounted to said housing and mounted to said ceiling with said housing removably attached to said junction box.

17. The ceiling lighting system of claim 11, wherein said housing is mounted such that said housing is in direct contact with said ceiling.

18. A solid state light fixture, comprising: a solid state lighting housing comprising an open end, a base end, and an interior surface, said housing defining an optical chamber between said open end and said base end; a plurality of light emitting diodes within said optical chamber and emitting light out of said housing open end; a driver circuit within said optical chamber; a reflector cone between said open end and said base end, said light emitting diodes emitting light during operation such that at least some light is reflected by said reflector cone and at least some light is reflected by said interior surface of said housing; a junction box on said housing; and at least one mounting mechanism operable to mount said fixture in an opening in a ceiling with said open end adjacent the ceiling surface around said ceiling opening.

19. The light fixture of claim 18, wherein said mounting mechanism urges said open end adjacent said ceiling surface.

20. The light fixture of claim 18, wherein said mounting mechanism urges said open end against the ceiling surface around said ceiling opening.

21. The light fixture of claim 18, wherein said mounting mechanism comprises springs or spring clips.

22. The light fixture of claim 18, wherein said fixture is mounted directly in said ceiling.

23. The light fixture of claim 18, mounted in said ceiling opening such that said housing is in direct contact with said ceiling.

24. The light fixture of claim 11, wherein said housing further comprises an exterior surface opposite said reflective interior surface, and wherein said exterior surface is an outside surface of said light fixture.

25. The light fixture of claim 11, said reflective interior surface extending from a perimeter of said base to said open end.

26. The light fixture of claim 11, wherein said base and said reflective interior surface are contiguous.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective view of a lighting device according to an embodiment of the present invention.

(2) FIG. 2 is a perspective view of a lighting device according to an embodiment of the present invention.

(3) FIG. 3 is a perspective view of the lighting device according to an embodiment of the present invention with a portion removed to expose internal elements.

(4) FIG. 4 is a perspective view of a lighting device according to an embodiment of the present invention.

(5) FIG. 5 is a top view of a circuit element for use in lighting devices according to embodiments of the present invention.

(6) FIG. 6 is a perspective view of a circuit element mounted to the base of a housing.

(7) FIG. 7 is a cross-sectional view of a lighting device in one mount configuration according to an embodiment of the present invention.

(8) FIG. 8 is a cross-sectional view of a lighting device in another mount configuration according to an embodiment of the present invention.

(9) FIG. 9 is a perspective view of the bottom side of a lighting device according to an embodiment of the present invention.

(10) FIG. 10 is a side perspective view of a lighting device according to an embodiment of the present invention.

(11) FIG. 11 is an exploded view of a lighting device according to an embodiment of the present invention.

(12) FIG. 12 is a bottom perspective view of a lighting device according to an embodiment of the present invention.

(13) FIG. 13 is a cross-sectional view of the base portion of a lighting device according to an embodiment of the present invention.

(14) FIG. 14 is a block diagram of a circuit that may be used in embodiments of the present invention.

(15) FIG. 15 is a diagram of a driver circuit that may be used in embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(16) Embodiments of the invention provide a solid state lighting fixture with an integrated driver circuit. A housing designed to protect the light sources and the electronic components has a base end and an open end through which light is emitted from the fixture. The reflective interior surface of the fixture and the base define an optical chamber. At least one, and often multiple, light sources are mounted at the fixture base along with the circuitry necessary to drive and/or control the light sources. In order to minimize the overall size of the fixture, the drive circuit and the light sources are both located in the optical chamber. A reflective cone fits within the optical chamber such that it covers most of the drive circuit and other components at the base of fixture that might absorb light. The reflective cone is shaped to define a hole that is aligned with the light sources so that light may be emitted through the hole toward the open end of the fixture.

(17) Embodiments of the present invention are described herein with reference to conversion materials, wavelength conversion materials, phosphors, phosphor layers and related terms. The use of these terms should not be construed as limiting. It is understood that the use of the term phosphor or phosphor layers is meant to encompass and be equally applicable to all wavelength conversion materials.

(18) It is understood that when an element is referred to as being on another element, it can be directly on the other element or intervening elements may also be present. Furthermore, relative terms such as inner, outer, upper, above, lower, beneath, and below, and similar terms, may be used herein to describe a relationship of one element to another. It is understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

(19) Although the ordinal terms first, second, etc., may be used herein to describe various elements, components, regions and/or sections, these elements, limited by these terms. These terms are only used to distinguish one element, component, region, or section from another. Thus, unless expressly stated otherwise, 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.

(20) As used herein, the term source can be used to indicate a single light emitter or more than one light emitter functioning as a single source. For example, the term may be used to describe a single blue LED, or it may be used to describe a red LED and a green LED in proximity emitting as a single source. Thus, the term source should not be construed as a limitation indicating either a single-element or a multi-element configuration unless clearly stated otherwise.

(21) The term color as used herein with reference to light is meant to describe light having a characteristic average wavelength; it is not meant to limit the light to a single wavelength. Thus, light of a particular color (e.g., green, red, blue, yellow, etc.) includes a range of wavelengths that are grouped around a particular average wavelength.

(22) Embodiments of the invention are described herein with reference to cross-sectional view illustrations that are schematic illustrations. As such, the actual thickness of elements can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances are expected. Thus, the elements 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.

(23) FIG. 1 is a perspective view of a lighting device 100 according to an embodiment of the present invention. A housing 102 comprises a base 104 and an open end 106 through which light is emitted during operation. A junction box 108 is detachably mounted to the housing 102. The junction box 108 has a mount mechanism (not shown) for mounting to an external surface, such as a ceiling or a wall, for example. The junction box 108 can be mounted to an external structure using screws, wires, straps, and many other known attachment mechanisms. The junction box 108 should be easily detachable and re-attachable to the base 104 to allow for easy access to the junction box 108 for maintenance. Because the junction box 108 can remain attached to the external structure, it is also easy to remove, repair, and/or replace the housing 102 or any of its internal components. In this embodiment, spring clips 109 are used to mount the device 100 to the ceiling drywall or the insulation tile, for example, eliminating the need for a can recess in the ceiling. Other mount structures may be suitable.

(24) The lighting device 100 and other embodiments of the present invention provide a variety of advantages over traditional fixtures. During remodeling of a commercial or residential space, for example, it may not initially be known that there is not enough space or that there may be obstructions (e.g., piping, wiring, ductwork) that would prevent the use of a housing (can) in the ceiling. In many instances, this is discovered after cutting a hole in the ceiling. Some embodiments of the invention eliminate the need for the housing (can) altogether. This would be very important for consumers as material and installation costs associated with the fixture are reduced. For example, attaching a junction box 108 to the fixture provides enough space to terminate the electrical wiring. The junction box 108 may be detachable allowing for easy maintenance or replacement. In some embodiments, a junction box may be located on the side of the fixture to minimize the height of the fixture. The device 100 may be mounted with spring clips directly to the ceiling tile or drywall (as shown in FIG. 7). Since solid state light sources are efficient and the temperature range of the device 100 is within safe limits, insulation can be placed around it. Thus, embodiments of the present invention may pose less of a fire hazard than typical incandescent downlights. Additionally, these embodiments allow for quicker installation and subsequent safety inspection.

(25) FIG. 2 is a perspective view of the lighting device 100. The housing 102 and the interior surface of the base 104 are shaped to define an optical chamber 110. The interior surface of the housing 102 is reflective and shaped to redirect light out of the open end 10 to create a desired output profile. A reflector cone 112 fits inside the housing 102 and functions to cover the driver circuit 116 and any other absorptive elements at the base 104 of the housing, as best shown in FIGS. 3 and 4. The interior surface of reflector cone 112 is shaped to create a smooth surface transition at the intersection with the interior surface of the housing 102. The reflector cone 112 can be held in place inside the housing 102 using an adhesive, screws, or a snap-fit groove structure, for example.

(26) FIG. 3 is a perspective view of the lighting device 100, looking into the open end 106 with the reflector cone 112 removed to expose the elements disposed in the base 104. This particular embodiment comprises five LEDs 114 disposed at the base 104 in the optical chamber 110. There can be more or fewer than five light sources in other embodiments. Here, the LEDs 114 and the driver circuit 116 are on a single circuit board with the LEDs 114 disposed in the middle portion of base 104 and surrounded by elements of the drive circuit 116 which powers and controls the output of the LEDs 114. Many driver circuits may be used, with some suitable circuits discussed in more detail herein. In other embodiments the LEDs and the driver circuit may be mounted on separate boards as discussed in more detail herein. As shown, both the LEDs 114 and the drive circuit 116 are housed within the optical chamber 110. This compact arrangement obviates the need for a separate recessed can (i.e. 4 or 6 recessed housing commonly used for recessed downlights) to hold the device 100. Thus, lighting devices according to embodiments of the invention are lightweight, have reduced height, and are easier to install.

(27) The reflector cone 112 is shown removed from the housing 102. The reflector cone 112 is shaped to define a hole 118. When the reflector cone 112 is mounted inside the housing 102, the hole 118 aligns with the LEDs 114, and in some embodiments, the LEDs 114 protrude through the hole 118 into the optical chamber 110. Thus, when mounted the reflector cone 112 prevents light emitted from the LEDs 114 from being absorbed by any elements of the drive circuit 116 by shielding off those absorptive elements from the rest of the optical chamber 110. In this particular embodiment, a flange 120 of reflector cone 118 is mounted with screws or pins to a ridge 120 on the interior of the housing 102. In some embodiments the reflective cone may be omitted for cost savings, and the drive circuit may be covered by a reflective paint. Other structures and/or materials may also be used to reflect light away from the drive circuit 116.

(28) FIG. 4 is a perspective view of another lighting device 200 according to an embodiment of the present invention. In this view, a portion of the reflector cone 112 has been removed to reveal the elements beneath. The device 200 shares several elements in common with the device 100; thus, like elements are identified using the same reference numerals. This particular embodiment comprises LEDs 114 on a first circuit board 202 and the driver circuit 116 on a second circuit board 204. The first circuit board 202 is under the second circuit board 204 with a spacer (not shown) between the two boards 202, 204 to provide electrical isolation. In this embodiment, the second board 204 which contains the driver circuit 116 comprises two halves 204a, 204b with a cutout portion in the center. All of the driver circuit 116 elements are on one half of the second board 204a. The other half 204b comprises a piece of metal, such as copper, for thermal dissipation. The LEDs 114 are on the first board 202 and protrude up through the cutout portion of the second board 204 as shown. The LEDs then further protrude up through the hole in the reflector cone 112 (not shown due to the removed portions of the reflector cone 112 in this figure). In this embodiment, spring clips 109 are used to mount the device 200 to the ceiling drywall or the insulation tile, although other mount structures may be suitable.

(29) FIG. 5 is a top view of a circuit element 500 for use in lighting devices according to embodiments of the present invention. The element 500 provides a surface for a plurality of LEDs 502 and various driver circuit components 504 are disposed. In this embodiment, the LEDs and the driver circuit 504 are disposed on the same circular circuit board 506. The circuit board is shaped to fit in the base of a housing similar to the housing 102 shown in FIG. 1. The driver circuit components 504 are arranged around the perimeter of the circuit board 506 with the LEDs 502 in the middle portion. Four bore holes 508 are cut from the circuit board 506 to allow for mounting to a housing using screws, pins, or the like. Leads 510 connect the LEDs 502 and the driver circuit 504 to an external power source through a junction box in some embodiments.

(30) The circuit element can be mounted to a housing using various mechanisms. FIG. 6 is a perspective view of the circuit element 500 mounted to the base of a housing 602 with washer/screws 604. Here, the reflector cone has been removed completely. Indeed, the reflector cone is excluded from some embodiments altogether.

(31) FIG. 7 is a cross-sectional view of the lighting device 100 in one mount configuration according to an embodiment of the present invention. In this configuration the base 104 protrudes through the ceiling 702 into the plenum. The open end 106 is exposed beneath the ceiling 702 so the light is emitted into the room. The spring clips 109 urge the open end 106 of the housing 102 up against the ceiling, holding the lighting device 100 firmly against the ceiling 702. The portion of the lighting device 100 in the plenum above the ceiling 702 is surrounded by insulation 704.

(32) FIG. 8 is a cross-sectional view of the lighting device 100 in another mount configuration according to an embodiment of the present invention. In this configuration, the junction box 108 is mounted directly to the ceiling with screws or the like. The housing 102 is removably attached to the junction box 108. In some cases, the junction box 108 may already be present at the ceiling during installation in which case the housing 102 is attached thereto. However, the junction box 108 and the housing 102 may be installed as a single unit.

(33) FIG. 9 is a perspective view of the bottom side of a lighting device 900 according to an embodiment of the present invention. The device 900 comprises a housing having a base 904 (shown in FIG. 10) and an open end 906. Embodiments such as the device 900 may be described as a disc light. Disc lights are discussed generally in U.S. application Ser. No. 13/365,844 titled LIGHTING DEVICE AND METHOD OF INSTALLING LIGHT EMITTER, which is commonly assigned with the present application and incorporated by reference herein. The housing 902 is shaped to define an optical chamber which is obscured in this view by a lens plate 908. An electrical connector 910 is used to connect the device 900 to an external power source, for example, in a junction box. In some embodiments, the connector 910 can connect to an adapter that interfaces with a standard Edison screw socket such that the device 900 can be easily integrated into existing electrical architecture where traditional incandescent bulbs had been previously used.

(34) The lens plate 908 is used to further mix the outgoing light and reduce imaging of the sources in the optical chamber (i.e., hotspots). In this embodiment, the plate 908 is attached to the housing 902 with a snap-fit connection. In other embodiments, the plate 908 may be attached to the housing with an adhesive, screws, or the like. Here, the lens plate 908 comprises a diffusive element. The lens plate 908 functions in several ways. For example, it can prevent direct visibility of the sources 918 and provide additional mixing of the outgoing light to achieve a visually pleasing uniform source. However, a diffusive lens plate can introduce additional optical loss into the system. Thus, in embodiments where the light is sufficiently mixed by a reflector cone or by other elements within the optical chamber, a diffusive lens plate may be unnecessary. In such embodiments, a transparent glass lens plate may be used, or the lens plates may be removed entirely. In still other embodiments, scattering particles may be included in the lens plate.

(35) Diffusive elements in the lens plate 908 can be achieved with several different structures. A diffusive film inlay can be applied to the top- or bottom-side surface of the lens plate 908. It is also possible to manufacture the lens plate 908 to include an integral diffusive layer, such as by coextruding the two materials or insert molding the diffuser onto the exterior or interior surface. A clear lens may include a diffractive or repeated geometric pattern rolled into an extrusion or molded into the surface at the time of manufacture. In another embodiment, the lens plate material itself may comprise a volumetric diffuser, such as an added colorant or particles having a different index of refraction, for example.

(36) In other embodiments, the lens plate 908 may be used to optically shape the outgoing beam with the use of microlens structures, for example. Many different kinds of beam shaping optical features can be included integrally with the lens plate 908.

(37) FIG. 10 is a side perspective view of the lighting device 900. The base 912 of the housing 902 surrounds the electronics and the light sources that are disposed in the optical chamber. The device 900 may be connected directly to a surface such as a ceiling, a wall, or a junction box, or it mounted such that the base 912 extends through the ceiling and into the plenum in which case it may be mounted using clips similarly as device 100 shown in FIG. 7.

(38) The device 900 has a compact profile such that it can easily fit within existing fixture spaces. Embodiments of the invention provide for a downlight fixture in which the light sources (e.g., LEDs) and the driver circuitry can be housed in the optical chamber which is recessed from the ceiling plane. A recessed fixture is desirable from an architectural perspective as the glare is reduced for the occupants in a living or work space. In some LED fixtures, the driver circuitry is mounted outside the optical chamber which increases the overall height of the fixture. In many buildings there is not enough space above the ceiling to accommodate such a fixture. Embodiments of the present invention provide a fixture with reduced height such that it can be used even when plenum space is limited.

(39) FIG. 11 is an exploded view of the lighting device 900. The lens plate 908 and a reflector cone 914 have been removed to reveal electronic components including a driver circuit 916 and a plurality of LED light sources 918 mounted to the inside surface of the housing base 912. In this particular embodiment, five LED light sources 918 are mounted on the base 912 in the optical chamber, although it is understood that various different configurations with any number of light sources may be used. The reflector cone 914 is shaped to define a hole that aligns with the light sources 918 when the reflector cone 914 is attached to the housing 902.

(40) The reflector cone 914 comprises a reflective inner surface that functions to redirect light emitted from the sources 918 away from absorptive elements at the housing base 912, such as the driver circuit 916. Thus, the reflector cone 914 surface may comprise a diffuse white reflector such as a microcellular polyethylene terephthalate (MCPET) material or a Dupont/WhiteOptics material, for example. Other white diffuse reflective materials can also be used.

(41) Diffuse reflective coatings mix the light from solid state light sources having different spectra (i.e., different colors). These coatings are particularly well-suited for multi-source designs where two different spectra are mixed to produce a desired output color point. For example, LEDs emitting blue light may be used in combination with LEDs emitting yellow (or blue-shifted yellow) light to yield a white light output. A diffuse reflective coating may eliminate the need for additional spatial color-mixing schemes that can introduce lossy elements into the system; although, in some embodiments it may be desirable to use a diffuse reflector cone in combination with other diffusive elements. For example, in this particular embodiment, the reflector cone 914 is paired with the diffuser plate 908 to effectively mix the outgoing light.

(42) By using a diffuse white reflective material for the reflector cone 914 several design goals are achieved. For example, the reflector cone 914 performs a color-mixing function. A diffuse white material also provides a uniform luminous appearance in the output.

(43) The reflector cone 914 can comprise materials other than diffuse reflectors. In other embodiments, the reflector cone 914 can comprise a specular reflective material or a material that is partially diffuse reflective and partially specular reflective. In some embodiments, it may be desirable to use a specular material in one area and a diffuse material in another area. For example, a semi-specular material may be used on the center region with a diffuse material used in the side regions to give a more directional reflection to the sides. Many combinations are possible. It may also be desirable to texture the inner surface of the reflector cone 914 to achieve a desired optical effect.

(44) FIG. 12 is a bottom perspective view of the lighting device 900. In this view the lens plate 908 is removed to reveal the optical chamber. Here, the reflector cone 914 is mounted to the base 912 within the optical chamber. The light sources 918 are arranged at the base of the chamber. The reflector cone 914 hole is aligned with the sources 918 such that they protrude through the reflector cone 914 hole into the optical chamber, and the driver circuit 916 is obscured from view by the reflector cone 914.

(45) FIG. 13 is a cross-sectional view of the base portion of a lighting device 1300 according to an embodiment of the present invention. In this embodiment, the housing 1302 comprises a raised mount surface 1304 in the center of the housing base. The raised surface 1304 defines a circular cavity 1306 running around the perimeter of the housing base. A single circuit board 1308 provides the mount surface for the LEDs 1310 and the driver circuit components 1312. Similarly as in the circuit element 500, the driver circuit components 1312 are arranged around the perimeter of the board 1308. The circular cavity 1306 beneath provides space below the driver circuit components 1312, allowing for the use of through-hole components 1314 and, thus, a double-sided circuit board. The cavity 1306 provides electrical isolation for any through-hole and/or backside components from the housing 1302. In some embodiments a metal core circuit board may be used to facilitate thermal dissipation from the LEDs 1310 to the housing 1302. Here, a metal slug 1316, for example copper, is disposed between the LEDs 1310 and the housing to provide a bulk low-thermal resistance pathway from the heat-generating LEDs 1310 to the housing 1302. The reflector cone 1318 is arranged to shield light emitted from the LEDs 1310 from the absorptive elements such as the circuit board 1308 and the driver circuit components 1312.

(46) Various driver circuits may be used to power the light sources. Suitable circuits are compact enough to fit within the base of a particular housing while still providing the power delivery and control capabilities necessary to drive high-voltage LEDs, for example. FIG. 14 is a block diagram of a circuit 1400 that may be used in embodiments of the present invention. An AC line voltage V.sub.ac comes in where it is converted to DC at the AC to DC converter 1402. The resulting DC voltage is then either adjusted up or down with a DC to DC converter 1404 to meet the requirements of the light source 1406.

(47) At the most basic level a driver circuit may comprise an AC to DC converter, a DC to DC converter, or both. In one embodiment, the driver circuit comprises an AC to DC converter and a DC to DC converter both of which are located inside the optical chamber. In another embodiment, the AC to DC conversion is done remotely (i.e., outside the optical chamber), and the DC to DC conversion is done at the control circuit inside the optical chamber. In yet another embodiment, only AC to DC conversion is done at the control circuit within the optical chamber.

(48) Referring to both FIGS. 14 and 15, this particular embodiment of the driver circuit 1400 includes a rectifier as the AC to DC converter 1402 that is configured to receive an AC line voltage. The AC to DC converter 1402 may be a full-wave bridge rectifier as shown in FIG. 15 and is referred to as such in this embodiment. The output of the rectifier 1402, which may be a full-wave rectified AC voltage signal, is provided to the DC to DC converter 1404 which can be a switched-mode power supply, for example, and is referred to as such in this embodiment. In response to the rectified AC signal, the switched-mode power supply 1404 generates a DC voltage that is supplied to the light source 1406.

(49) As shown in FIG. 15, an EMI filter 1408 including a series inductor L1 and a shunt capacitor C1 may be provided at an input to the switched-mode power supply 1404. The EMI filter 1408 is a low pass filter that filters electromagnetic interference from the rectified line voltage.

(50) In some embodiments, the switched-mode power supply 1404 is a boost circuit including a boost inductor L2, a switch Q1, a boost diode D1 and a boost or output capacitor C2. The switch Q1 may be a MOSFET switch. The boost inductor L2 may include a transformer having a primary winding and an auxiliary winding. The primary winding of the boost inductor is coupled at one end to the input of the switched-mode power supply 1404 and at the other end to the anode of the boost diode D1 and the drain of the switch Q1.

(51) Operation of the switched-mode power supply 1404 is controlled by boost controller circuitry 1410, which is coupled to the output of the rectifier 1402, the gate and source of the switch Q1, and the output of the switched-mode power supply 1404. In addition, the boost controller circuitry 1410 is coupled to the auxiliary winding of the boost inductor L2. However, the boost controller circuitry 1410 may not draw bias or housekeeping power from the auxiliary winding of the boost inductor L2.

(52) In one embodiment the boost controller, which may be implemented, for example, using a TPS92210 Single-Stage PFC Driver Controller for LED Lighting manufactured by Texas Instruments can be configured in a constant on time-boundary conduction mode. In this mode the switch Q1 is turned on for a fixed time (T.sub.on) allowing for a ramp up of the current in the inductor L2. The switch Q1 is turned off and the inductor current ramps down to zero while supplying current to the output capacitor C2 through D1. The controller detects when the current falls to zero and initiates another turn-on of Q1. The peak input current in a switching period is given by given by V.sub.in*T.sub.on/L which is proportional to V.sub.in. Although the switching frequency varies over the line period, the average input current remains near sinusoidal and achieves a close to unity power factor.

(53) In another embodiment, a boost controller, such as an L6562 PFC controller manufactured by STMicroelectronics, can be used in constant off-time continuous conduction mode. In this mode, the current reference for the switch current is obtained from the input waveform. The switch is operated with a fixed off time. In another embodiment, the average inductor current is sensed with a resistor, and is controlled to follow the sinusoidal input voltage with a controller IC such as an IRF1155S manufactured by International Rectifier. Any of these controllers can be operated in constant power mode by operating them in open loop and fixing the controller reference, such as on-time or error-amplifier output, to a value that determines the power. The power transferred to the output is dumped into the load LEDs, which clamp the output voltage and in doing so define the output current.

(54) Although a connection is shown from the auxiliary winding of L2 to the boost controller 1410, a power factor compensating (PFC) boost converter for an LED driver circuit according to some embodiments may not draw bias or housekeeping power from the auxiliary winding of the boost converter. Rather, the boost controller may draw the auxiliary power from bottom of the LED string or from the drain node of the switch. Moreover, a PFC boost converter for an LED driver according to some embodiments may not use feedback from the LED voltage (VOUT) to control the converter.

(55) The boost circuit 1404 steps up the input voltage using basic components, which keeps the cost of the circuit low. Moreover, additional control circuitry can be minimal and the EMI filter 1408 can be small.

(56) The boost circuit 1404 achieves high efficiency by boosting the output voltage to a high level (for example about 170V or more). The load currents and circuit RMS currents can thereby be kept small, which reduces the resulting I.sup.2R losses. An efficiency of 93% can be achieved compared to 78-88% efficiency of a typical flyback or buck topology.

(57) The boost converter 1404 typically operates from 120V AC, 60 Hz (169 V peak) input and converts it to around 200V DC output. Different output voltages within a reasonable range (170V to 450V) can be achieved based on various circuit parameters and control methods while maintaining a reasonable performance. If a 230V AC input is used (such as conventional in Europe), the output may be 350V DC or higher.

(58) In one embodiment the boost converter is driven in constant power mode in which the output LED current is determined by the LED voltage. In constant power mode, the boost controller circuitry may attempt to adjust the controller reference in response to changes in the input voltage so that the operating power remains constant.

(59) When operated in constant power mode, a power factor correcting boost voltage supply appears nearly as an incandescent/resistive load to the AC supply line or a phase cut dimmer. In case of a resistive load, the input current has the same shape as the input voltage, resulting in a power factor of 1. In constant power mode the power supply circuit 1404 and light source 1406 offer an equivalent resistance of approximately 1440 at the input, which means 10 W of power is drawn from the input at 120V AC. If the input voltage is dropped to 108V AC, the power will drop to approximately 8.1 W. As the AC voltage signal on the input line is chopped (e.g. by a phase cut dimmer), the power throughput gets reduced in proportion and the resulting light output by the light source 1406 is dimmed naturally. Natural dimming refers to a method which does not require additional dimming circuitry. Other dimming methods need to sense the chopped rectified AC waveform and convert the phase-cut information to LED current reference or to a PWM duty cycle to the dim the LEDs. This additional circuitry adds cost to the system.

(60) A boost converter according to some embodiments does not regulate the LED current or LED voltage in a feedback loop. That is, the boost converter may not use feedback from the LED voltage (VOUT) to control the converter. However both of these inputs could be used for protection such as over-voltage protection or over-current protection. Since the boost converter operates in open loop, it appears as a resistive input. When a PWM converter controls its output voltage or output current and when the input voltage is chopped with a dimmer, it will still try to control the output to a constant value and in the process increase the input current.

(61) More details of circuits similar to the circuit 1400 are given in U.S. application Ser. No. 13/662,618 titled DRIVING CIRCUITS FOR SOLID-STATE LIGHTING APPARTUS WITH HIGH VOLTAGE LED COMPONENTS AND RELATED METHODS, which is commonly owned with the present application by CREE, INC., which was filed on 29 Oct. 2012, and which is incorporated by reference as if fully set forth herein.

(62) Additional details regarding driver circuits are given in U.S. application Ser. No. 13/462,388 titled DRIVER CIRCUITS FOR DIMMABLE SOLID STATE LIGHTING APPARATUS, which is commonly owned with the present application by CREE, INC., which was filed on 2 May 2012, and which is incorporated by reference as if fully set forth herein.

(63) Additional details regarding driver circuits are given in U.S. application Ser. No. 13/207,204 titled BIAS VOLTAGE GENERATION USING A LOAD IN SERIES WITH A SWITCH, which is commonly owned with the present application by CREE, INC., which was filed on 10 Aug. 2011, and which is incorporated by reference as if fully set forth herein.

(64) It is understood that embodiments presented herein are meant to be exemplary. Embodiments of the present invention can comprise any combination of compatible features shown in the various figures, and these embodiments should not be limited to those combinations expressly illustrated and discussed. For example, many different driver circuits and LED components may be used without departing from the scope of the invention. Although the present invention has been described in detail with reference to certain configurations thereof, other versions are possible. Therefore, the spirit and scope of the invention should not be limited to the versions described above.