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`US 20070069663Al
`
`c19) United States
`c12) Patent Application Publication
`Burdalski et al.
`
`c10) Pub. No.: US 2007 /0069663 Al
`Mar. 29, 2007
`(43) Pub. Date:
`
`(54) SOLID STATE LED BRIDGE RECTIFIER
`LIGHT ENGINE
`
`(76)
`
`Inventors: Robert J. Burdalski, Lumberton, NJ
`(US); Joseph B. Mazzochette, Cherry
`Hill, NJ (US)
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`(2006.01)
`HOSB 39100
`(52) U.S. Cl. .............................................................. 315/312
`
`Correspondence Address:
`PATENT DOCKET ADMINISTRATOR
`LOWENSTEIN SANDLER PC
`65 LIVINGSTON AVENUE
`ROSELAND, NJ 07068 (US)
`
`(21) Appl. No.:
`
`111443,535
`
`(22) Filed:
`
`May 30, 2006
`
`Related U.S. Application Data
`
`(60) Provisional application No. 60/685,680, filed on May
`27, 2005.
`
`(57)
`
`ABSTRACT
`
`A solid-state light engine comprised of light emitting diodes
`(LEDs) configured into a bridge rectifier with a current
`limiting module coupled to the LED bridge rectifier. The
`light engine may be packaged for high temperature opera(cid:173)
`tion. Optionally, the LEDs comprise wavelength-converting
`phosphors with a persistence that is a multiple of the peak to
`peak current period, to smooth and mask ripple frequency
`pulsation of emitted light.
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`Patent Application Publication Mar. 29, 2007 Sheet 20 of 20
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`IPR PAGE 21
`
`

`
`US 2007 /0069663 Al
`
`Mar. 29, 2007
`
`1
`
`SOLID STATE LED BRIDGE RECTIFIER LIGHT
`ENGINE
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`[0001] This application claims the benefit of U.S. Provi(cid:173)
`sional Patent Application No. 60/685,680, filed May 27,
`2005, the entire disclosure of which is hereby incorporated
`by reference herein.
`
`BACKGROUND OF THE INVENTION
`
`[0002] 1. Field of the Invention
`
`[0003] Embodiments of the invention relate to a solid-state
`light engine that is directly compatible with alternating
`current (AC) input power, without the need for a separate
`rectification module, but that can also alternatively be pow(cid:173)
`ered by direct current (DC) input power.
`
`[0004] 2. Related Art
`
`[0005]
`In many lighting applications, solid-state light
`engines are superior to conventional incandescent lamps.
`Beneficially, solid-state light engines can, in certain circum(cid:173)
`stances, achieve an almost 20% improvement in efficiency
`and an extended lifetime (e.g. exceeding 50,000 hours) as
`compared to incandescent lamps.
`
`[0006] Traditional solid-state light engines are powered by
`a direct current or pulsating direct current drive. As such, to
`drive the light engine using an AC power source, the AC
`input line must first be conditioned. Power-conditioning
`commonly involves the rectification of AC input power,
`typically achieved by inserting rectifier diodes in a bridge
`configuration, as well as a means oflimiting current, such as
`a series resistance or reactance in the power path. However,
`the addition of such electronic components into the power
`path may increase manufacturing costs and complexity, and
`can cause a decrease in the lifetime (or time to failure) of the
`light engine, and can decrease efficiency due to power loss.
`
`[0007] To avoid the performance-related issues caused by
`the insertion of power conditioning elements into the power
`path, some standard solid-state light engines are powered
`directly from the AC line. However, the direct AC powering
`of a light engine causes the light output to pulsate at the
`frequency of the AC power source, typically in the range of
`50 to 60 Hz. This line frequency pulsation can produce eye
`fatigue or annoyance when viewed, even in cases where the
`engine is viewed for a short period of time.
`
`[0008] Accordingly, there is a need for a solid state light
`engine that is directly compatible with an AC input power
`source, which does not exhibit the deleterious pulsation
`effects generated by a direct AC powering arrangement,
`and/or which does not require the use of separate power
`conditioning or rectification circuitry.
`
`SUMMARY OF THE INVENTION
`
`[0009] Embodiments of the invention satisfy these and
`other needs. Embodiments of the invention relate to a solid
`state bridge rectifier light engine arrangement that may be
`powered directly by an AC input line, without the need for
`further power conditioning. Although full-wave bridge rec(cid:173)
`tifiers are known in the art, they utilize non-light emitting
`diodes, and are used to convert AC current to DC current for
`
`use as a power source for external electronic components,
`not to produce useful illumination. Similarly, although the
`use of LEDs for illumination is known in the art, LEDs are
`typically powered by a DC power source. The present
`invention advantageously uses LEDs in a novel way by
`configuring them into a bridge rectifier to produce useful
`light directly from an AC power source without the need for
`separate rectification or other conditioning of the input
`power.
`
`[0010] More specifically, embodiments of the invention
`provide for a solid state light engine arrangement that
`includes a full wave bridge rectifier configuration of light
`emitting diodes (LEDs) directly compatible with an AC
`power input, which may advantageously also be connected
`to a current limiting element. An added benefit to this
`configuration is that the light engine may be constructed
`with two sets of terminals for connection to a power source,
`so that the user has the option of powering the light engine
`by either AC power or the more traditional DC power,
`depending on the terminals to which the user connects the
`power source.
`
`[0011] Embodiments of the invention can also include a
`solid-state LED bridge rectifier circuit advantageously using
`phosphors to further smooth any frequency pulsation or
`ripple oflight emitted from the light engine. The LED bridge
`rectifier can include one or more LEDs configured such that
`the LED bridge rectifier receives and rectifies an AC power
`signal and emits light. The current limiting module can be
`used to protect the LEDs by limiting the current passing
`through the LEDs within the LED bridge rectifier. The LEDs
`can emit any of a number of colors oflight, depending on the
`type of LED used. Advantageously, LEDs that emit of blue
`and/or ultraviolet wavelength emissions can be used, in
`combination with wavelength converting phosphors known
`in the art, to create light that is perceived as white light by
`a user. See, for example, U.S. Pat. No. 5,998,925 to Shimizu.
`The converting phosphor can be particles of Cerium acti(cid:173)
`vated Yttrium Aluminum Garnet (YAG:Ce) or Europium
`activated Barium Orthosilicates (BOSE).
`
`[0012] The turn-on and turn-off time for typical LEDs is in
`the tens to one hundred nanosecond range. With this
`response time, LEDs will virtually follow the low frequency
`AC waveform without delay. According to an aspect of an
`embodiment of the invention, through rectification, the light
`pulsation or ripple frequency will typically be increased to
`approximately twice the frequency of the input AC line
`current (e.g., 100 to 120 Hz). This frequency doubling has
`the advantageous effect of speeding up the light pulsation to
`a frequency beyond what is typically perceptible to human
`observers, thus making it more appealing for use in standard
`lighting applications than would an LED array powered
`directly from AC current that was not configured into a
`bridge rectifier. In addition, the frequency doubling that
`occurs in the LED bridge rectifier configuration results in a
`shortening of the time duration between current peaks to
`about 10 ms for a 50 Hz line and about 8 ms for a 60 Hz line.
`The shortened peak to peak period, together with the advan(cid:173)
`tageous use of phosphors having a persistence of 5 to 10
`times that duration, masks the light pulsation or flicker,
`allowing it to be smoothed and integrated into a nearly
`continuous white light output. Phosphors having a longer or
`shorter persistence may also be used advantageously.
`
`IPR PAGE 22
`
`

`
`US 2007 /0069663 Al
`
`Mar. 29, 2007
`
`2
`
`[0013] The light engine arrangement according to certain
`embodiments of the invention can be used as a solid-state
`replacement for conventional Edison-base incandescent
`lamps or as a replacement for low-voltage halogen lamps or
`other low voltage lamps. Advantageously, since no addi(cid:173)
`tional electronic components need be inserted into the power
`path, the increased useful life offered by the solid state light
`engine need not be compromised.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0014] The invention can be understood from the detailed
`description of exemplary embodiments presented below,
`considered in conjunction with the attached drawings, of
`which:
`
`[0015] FIG. 1 is a basic schematic of a solid state light
`engine in accordance with embodiments of the invention;
`
`[0016] FIG. 2 is a more detailed schematic of a solid state
`light engine, in accordance with embodiments of the inven(cid:173)
`tion;
`
`[0017] FIG. 3 is a circuit diagram of a solid state light
`engine, in accordance with embodiments of the invention;
`
`[0018] FIG. 4 is a graphical representation of the emis(cid:173)
`sions of various structures;
`
`[0019] FIG. 4a is a diagram showing alternative exem(cid:173)
`plary dispositions of phosphor particles for use with LEDs
`in the present invention;
`
`[0020] FIG. 5 is a circuit diagram of a solid state light
`engine, in accordance with embodiments of the invention;
`
`[0021] FIG. 6 is a graphical representation of peak current
`through a device, in accordance with embodiments of the
`invention;
`
`[0022] FIGS. 7-11 are circuit diagrams of solid state light
`engines, each having a different current limiting module
`attached thereto, in accordance with embodiments of the
`invention;
`
`[0023] FIG. 12 is a circuit diagram of a solid state light
`engine, being powered by a DC power source, in accordance
`with embodiments of the invention;
`
`[0024] FIGS. 13-17 are circuit diagrams of solid state light
`engines, each being driven by a low voltage AC power
`source, in accordance with embodiments of the invention;
`
`[0025] FIGS. l8a-l8d are circuit diagrams of alternate
`implementations of solid state light engines, in accordance
`with embodiments of the invention;
`
`[0026] FIGS.19a-19b are diagrams of exemplary embodi(cid:173)
`ments of LED packaging for high temperature operation that
`may advantageously be adapted to use in the present inven(cid:173)
`tion.
`
`to be understood that the attached drawings are for
`[0027]
`purposes of illustrating the concepts of the invention and
`may not be to scale.
`
`violet wavelength emission which stimulates a phosphor, or
`some mixture of phosphors, that emit light in the green,
`yellow and/or red wavelengths. The combination of all these
`wavelengths is perceived as white light by the human eye.
`If one were to look at just a monochrome color LED driven
`with an AC source, one would see the pulsation of the light
`at the 50 Hz or 60 Hz frequencies. Even if the pulsation is
`above the detectable threshold to 100 Hz or 120 Hz, the
`pulsation can still be detected when the light interacts with
`objects or images moving or pulsating at close to the LED
`pulse rate or harmonics of that rate. This is, at the least,
`annoying and, at worst, potentially dangerous. Strobing light
`could possibly make moving or spinning objects appear to
`be not moving at all. An example of this is a fluorescent light
`source flickering at line frequency illuminating strobe marks
`on a turntable.
`
`[0029] With reference to FIG. 1, there is shown a solid(cid:173)
`state light engine comprising an LED bridge rectifier 100
`coupled to an optional current limiting module 200. The
`LED bridge rectifier is coupled to, and powered by, power
`supply module 10. LED bridge 100, comprising LEDs,
`emits light L, thus providing a usable light source.
`
`[0030] With reference to FIG. 2, LED bridge rectifier 100
`is shown in greater detail. Specifically, LED bridge rectifier
`100 can comprise four bridge legs 110, 120, 130, 140, each
`leg preferably including two or more LEDs. As such, in
`embodiments of the invention, each of legs 110, 120, 130
`and 140 can emit light when supplied with power at input 12
`from AC power supply module 10.
`
`[0031] FIG. 3 illustrates an exemplary embodiment of the
`invention in further detail. According to this embodiment,
`LED bridge rectifier 100 includes a full wave bridge con(cid:173)
`figuration, with each of the bridge legs 110, 120, 130, 140
`including LED modules 111, 112, 113, 121, 122, 123, 131,
`132, 133, 141, 142 and 143. Although FIG. 3 depicts three
`LEDs in each bridge leg, the LED bridge rectifier may be
`configured to include one or more multiple LEDs in each
`bridge leg. The number of LEDs (N) in any bridge leg may
`be determined by the desired luminous output and the input
`sinusoidal peak voltage of an AC power source applied
`between A Cl and AC2. The current limiting module 200 is
`connected to the rectified DC output of the LED bridge
`rectifier. Although as shown in FIG. 3 the current limiting
`module 200 is external in this embodiment, alternatively, it
`may be integrated into the light engine package (LED bridge
`rectifier 100).
`
`[0032] The reverse voltage seen by each leg 110, 120, 130,
`140 of the bridge module 100 is represented by the following
`equation:
`
`V,T~ V.n(RMS)*v2.
`Accordingly, the reverse voltage seen by each LED module
`111, 112, 113, 121, 122, 123, 131, 132, 133, 141, 142, 143
`of the bridge leg 110, 120, 130, 140 is represented by the
`following equation:
`
`V,d~V,T!N;
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`where N is the number of LED modules (LEDs) in a bridge
`leg 110, 120, 130, 140.
`
`[0028] Embodiments of the invention are directed to a
`solid state light engine producing white or near white light
`that is constructed by using LEDs that emit blue or ultra-
`
`[0033] Since typical LEDs do not have the capacity to
`withstand high reverse voltages, the number of LEDs in the
`array can be chosen to limit the reverse voltage on each LED
`
`IPR PAGE 23
`
`

`
`US 2007 /0069663 Al
`
`Mar. 29, 2007
`
`3
`
`to a safe (i.e., not damaging to the LEDs) level, as would be
`known to one of skill in the art, as informed by the present
`disclosure. In addition, because individual LEDs may
`exhibit differing leakage current levels under the same
`reverse voltage, in some embodiments, a shunt resistance or
`reactance network can be used to assure the total reverse
`voltage is distributed equally, as illustrated in FIG. 3.
`
`[0034] With reference to FIG. 4, as is depicted in the
`graphical representation 400, the above-described arrange(cid:173)
`ment of elements produces a pulsating emission from the
`LEDs 403 such that the pulsed emission is twice the input
`AC line frequency (100 Hz or 120 Hz). If the LEDs make
`use of phosphors, the phosphor particles becomes excited by
`each light pulse. The phosphor is chosen such that, besides
`its photometric and wavelength-converting characteristics, it
`preferably has a persistence (time constant) of greater than
`40 ms. Thus, the phosphor emission can persist while the
`LEDs are in the low output and off portion of their emission
`402. The end effect is perceived as white light emission
`without perceptible pulsation 401. The phosphor particles
`preferably have effective diameters smaller than 100
`microns, and more preferably, in the range 0.01 to 100
`microns.
`
`[0035] The phosphors can be disposed within a packaged
`LED array in several ways. Typically, in packaged LED
`assemblies, each LED die is encapsulated in an epoxy or
`silicone to protect the die from the environment, and option(cid:173)
`ally to serve as an optical element that may focus or
`otherwise direct the emitted light. Phosphor particles may be
`utilized in the LED package in a number of ways. For
`example, as can be seen in FIG. 4a, in an LED package 410,
`the phosphor particles 40 may be applied directly to the LED
`die 41 before the encapsulant 43 is applied, the phosphor
`particles forming a thin layer bonded to the LED die 41 by
`a layer of tacky uncured resin 42 that is later cured. The
`preferred tacky transparent materials include but are not
`limited to partially cured silicones or fully cured gel-like
`silicones with high refractive index (e.g., GE Silicones
`IVS5022 or Nusil Gel-9617-30). The silicones can include
`micro amino emulsions, elastomers, resins and cationics.
`Other useful polymeric resins include butyrals, cellulosic,
`silicone polymers, acrylate compounds, high molecular
`weight polyethers, acrylic polymers, co-polymers, and
`multi-polymers. The index of refraction of the above-men(cid:173)
`tioned materials can be tailored for optical matching.
`
`[0036] Alternatively, the phosphors particles 40a may be
`dispersed in the encapsulant 44, or applied overlying the
`encapsulant 44, either directly applied in a layer 40b to the
`outer surface of the encapsulant, or (not shown) in a second
`layer that may comprise an optical element.
`
`[0037] As illustrated in FIG. 5, and with continued refer(cid:173)
`ence to FIG. 3, according to an embodiment of the invention,
`current limiting module 200 can comprise a single resistor
`201 used to set the peak current for a given input voltage.
`According to an exemplary embodiment of the invention,
`the peak current per bridge leg 110, 120, 130, 140 may be
`set to:
`
`IfPcok~(Imc *1.57)/du,
`
`[0038] Where du, or duty factor, is the conduction time (t)
`divided by the total period (T).
`
`du~TIT,
`as is illustrated by graphical representation 600 of FIG. 6.
`
`[0039] The resistor value (R) of resistor RL is determined
`by the following equation:
`
`R~(V,n(Peak)-V rr)/IfPcok
`[0040] Alternative embodiments of the invention are
`depicted in FIGS. 7 to 11, each embodiment including a
`different exemplary current limiting module 200 for use in
`the solid state light engine arrangement of the invention. In
`all embodiments, the current limiting module 200 can be
`applied external to the light engine, or, alternatively, it may
`be integrated into the light engine package (i.e., LED bridge
`100).
`
`[0041] FIG. 7 depicts an implementation wherein current
`limiting module 200 is configured such that the resistive
`element RL of FIG. 3 is replaced with a capacitor CL 202,
`thereby forming a "lossless" current limiting element,
`wherein the reactance at the line frequency equivalent to the
`required resistance is given by the following equation:
`
`R~Xc, C~ll(2*n*F*Xc).
`
`[0042] FIG.8 depicts a solid state light engine according to
`an embodiment of the present invention wherein the current
`limiting module 200 is configured such that the resistive
`element RL of FIG. 3 is replaced with an inductor LL 203,
`thereby also forming a "lossless" current limiting element,
`wherein the reactance at the line frequency equivalent to the
`required resistance is given by the following equation:
`
`R~XL, L~Xcf(2*n*F).
`
`[0043] FIG. 9 depicts a solid state light engine according
`to an embodiment wherein the current limiting module 200
`is configured such that resistor RL of FIG. 3 is replaced with
`a positive temperature coefficient varistor VRL 204, to pro(cid:173)
`vide improved current limiting under widely varying AC
`voltage amplitude.
`
`[0044] FIG. 10 depicts a solid state light engine according
`to an embodiment wherein the current limiting module 200
`is configured such that resistor RL of FIG. 3 is replaced with
`the series combination of a capacitor CL with a negative
`temperature coefficient varistor VRL 205 to provide spike
`current protection and improved efficiency.
`
`[0045] FIG. 11 depicts a solid-state light engine arrange(cid:173)
`ment according to an embodiment wherein the current
`limiting module 200 comprises a current regulation circuit
`206, having a peak limit. This is possible since the current
`regulated by this circuit is on the rectified or DC side of the
`light engine, and the regulator will only see a pulsating DC
`current. As such, this type of regulator would typically be
`difficult to realize if it were required to be directly linked
`with AC current. This same circuit can be used to realize
`active current regulation to maintain nearly constant light
`output in response to varying AC amplitude, or to realize
`peak current limiting (clipping) for light engine protection
`under the same conditions, for improved efficiency.
`
`[0046] One having ordinary skill in the art will appreciate
`that alternative current limiting elements may be used in
`accordance with the solid-state light engine arrangement of
`embodiments of the invention.
`
`IPR PAGE 24
`
`

`
`US 2007 /0069663 Al
`
`Mar. 29, 2007
`
`4
`
`[0047] According to an embodiment of the invention, the
`circuit pictured in FIG. 3 can be alternatively powered by
`applying a DC bias from DC+ to DC-, as is depicted in FIG.
`12. In this embodiment, there would be no AC power source
`connected to AC3 and AC4. DC power supply module 12
`supplies power to LED bridge rectifier 101. This allows the
`embodiment of the light engine discussed above to be
`powered by "conventional" (i.e., via DC voltage supplies)
`methods. Such a configuration is also desirable to test the
`light engine, because it is simpler than procuring and using
`a current-controlled, sinusoidal power source.
`[0048] FIG. 13 illustrates an exemplary embodiment as
`applies to a low-voltage AC input application. In this
`embodiment, a low voltage AC power supply module 13
`provides power to LED bridge rectifier 102. In this embodi(cid:173)
`ment, the current limiting elements are inherent to the LED
`bridge rectifier 102 and are included in the same package.
`LEDs Dl through D4 form the rectifier bridge and feed
`LEDs D5 and D6, which are connected in parallel across the
`DC output terminals and act as the current limiting module.
`Each Dl/D4 and D2/D3 diode pair in the bridge conducts on
`alternate half cycles of the AC input and see the full peak
`current. Since the diode pairs conduct on half cycles, the
`duty factor seen by these LEDs is one-half the total duty
`factor referenced previously. This allows a higher than
`typical sinusoidal peak current with the resulting root-mean(cid:173)
`square (RMS) current reduced by the duty factor. LEDs D5
`and D6 see both half cycles but share the peak current, each
`seeing 1h Ipk' so the power dissipated is nearly equally
`distributed among the six LEDs. Using the LEDs on the
`rectified DC output side of the light engine has the benefit
`that, in addition to the LEDs being current-limiting ele(cid:173)
`ments, they also contribute to the total light output. This
`helps maximize efficiency. The embodiment shown is
`directly compatible with power supply modules 13 having
`low voltage AC lines in the 9 VAC to 12 VAC range, which
`is a popular low voltage lighting range. If required, a small
`resistance or voltage drop can be inserted in the DC path to
`trim the peak current to the desired level. The use of
`germanium, Schottky, Schottky Barrier, silicon or Zener
`diodes can provide voltage trimming from about 0.25 Volt to
`several Volts. A positive temperature coefficient varistor can
`provide peak current limiting under widely varying AC line
`amplitude. Alternative embodiments to the low voltage AC
`circuit of FIG. 13 are depicted in FIGS. 14 (with inline
`resistor R1301), 15 (with inline positive temperature coef(cid:173)
`ficient varistor VRL 302), 16 (with inline Zener diode
`D8303), and 17 (with inline diode D7304).
`[0049] FIGS. 18a through lSb illustrate alternative super(cid:173)
`position equivalents of the solid-state light engine emitter
`arrangements described above and depicted in previous
`figures.
`[0050] The above described LED bridge rectifier light
`engine can be manufactured using any method suitable for
`the assembly of LED arrays, including the use of pre(cid:173)
`packaged LEDs mounted on conventional printed wiring
`boards with other components. Alternatively, the above
`described LED bridge rectifier light engine can be manu(cid:173)
`factured in pre-packaged integrated arrays where LED dice
`are mounted on thermally-conductive substrates for heat
`management and integrated with other components.
`[0051] Preferably, the LED bridge rectifier light engine is
`made using packaging methods suitable for high tempera-
`
`ture operation LED light engines. In a typical high tempera(cid:173)
`ture package, LED dice are mounted, directly or indirectly,
`on a metal substrate layer that serves as a heat spreader or
`sink. Alternatively, non-metallic materials with proper heat
`conduction and strength properties may be used instead of a
`metal layer. The circuit traces in a high temperature package
`may be embedded in or imposed on ceramic layers or
`contained in a conventional printed wiring board layer or
`layers overlying the metal layer. The LED dice may be
`electrically connected to the circuit traces through methods
`known in the art, including use of lead frames, bonding
`wires, or other known methods. Other electronic compo(cid:173)
`nents may be mounted on the ceramic layers or printed
`wiring board, or mounted on the metal layer, directly or
`indirectly through an interposing element for electrical iso(cid:173)
`lation or other advantageous purposes.
`
`[0052]
`In a preferred embodiment, the LED bridge recti(cid:173)
`fier light engine can be fabricated using the packaging
`methods, including the low temperature co-fired ceramic(cid:173)
`on-metal (LTCC-M) technique, described in U.S. Patent
`Application Publication No. 2006/0006405, Mazzochette,
`"Surface mountable light emitting diode assemblies pack(cid:173)
`aged for high temperature operation," published Jan. 12,
`2006 ("Mazzochette"), the entire contents of which are
`hereby incorporated as if fully set forth at length herein.
`Although the description and diagrams in Mazzochette do
`not embody an LED bridge rectifier, one of skill in the art
`may readily adapt the disclosed packaging methods for use
`in the present invention.
`
`[0053] FIGS. 19a and 19b depict an alternative exemplary
`LED packaging method for high temperature operation that
`may advantageously be adapted to use with the present
`invention. Although the embodiments depicted in FIGS. 19a
`and 19b do not embody an LED bridge rectifier, one of skill
`in the art may readily adapt the disclosed packaging methods
`of FIGS. 19a and 19b for use in the present invention. In
`FIGS. 19a and 19b, the LED package comprises a metal
`layer 191, a printed wiring board (PWB) 192 having one or
`more layers and one or more apertures, the PWB being used
`to route wiring traces for interconnecting the LED dice 193
`and to mount and interconnect the other components used in
`the LED bridge rectifier. The printed wire board 192 overlies
`the metal layer 191. The metal layer 191, which preferably
`may comprise copper, serves as a thermally conductive
`mounting base that manages heat generated by the LED dice
`193 by spreading the heat and conducting it toward an
`optional external heat sink that may be mounted beneath the
`metal base. The package further comprises one or more
`isolators or interposers 194 in registration with the apertures
`of the PWB 192 and mounted on the metal layer 191. The
`LED dice 193 are mounted on the one or more isolators 194
`wherein the isolators 194 comprise a material having a
`thermal coefficient of expansion (TCE) that matches that of
`the LED dice 193 mounted thereon, thus managing any
`thermal mechanical stresses caused by the heat generated by
`the LED dice 193. Suitable TCE-matching materials that
`may be used in accordance with the present invention
`include, but are not limited to, copper-moybdenum-copper
`(CuMoCu), tungsten-copper (WCu), aluminum-silicon-car(cid:173)
`bide (AlSiC), aluminum nitride (AlN), silicon (Si), beryllim
`oxide (BeO), diamond, or other material that has a TCE that
`is matched to that of the LED die. Optionally, an encapsulant
`195 may be disposed over the LED dice 193.
`
`IPR PAGE 25
`
`

`
`US 2007 /0069663 Al
`
`Mar. 29, 2007
`
`5
`
`It is to be understood that the exemplary embodi(cid:173)
`[0054]
`ments are merely illustrative of the present invention. Many
`variations, modifications and improvements to the above(cid:173)
`described embodiments will occur to those skilled in the art
`upon reading the foregoing description and viewing the
`Figures. It should be understood that all such variations,
`modifications and improvements have not been included
`herein for the sake of conciseness and readability, but are
`properly within, and are intended to be within, the scope of
`the invention and the following claims.
`