Patent Publication Number: US-2012043897-A1

Title: Led circuits and assemblies

Description:
RELATED APPLICATIONS 
     The application is a continuation-in-part of U.S. patent application Ser. No. 12/287,267, filed Oct. 6, 2008, which claims the priority to U.S. Provisional Application No. 60/997,771, filed Oct. 6, 2007; this application also claims priority to U.S. Provisional Application No. 61/215,144, filed May 1, 2009; the contents of each of these applications are expressly incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to light-emitting diode (“LED”) circuits and assemblies; and more specifically to scalable alternating current (“AC”) driven LED circuits and assemblies. 
     SUMMARY OF THE INVENTION 
     While not intending to limit the scope of the claims or disclosure, in brief summary, the present disclosure and claims are directed to providing improved ease of designing and building lighting fixtures using AC-driven LEDs. Disclosed and claimed are LED circuits having scalable circuit configurations and LED package assembly configurations which can be used in an AC-drive platform to more easily match the voltage requirements of the lighting fixture(s) or systems in which the LED&#39;s are desired. Circuits and LED package assemblies are claimed and disclosed which reduce objectionable flicker produced from AC-driven LEDs and to produce more light per component. Packaged LED&#39;s are provided for lighting design according to the invention which address flicker at low frequencies (e.g. 50/60 Hz) while being scalable as desired for a particular lighting goal without resort to designing individual assemblies at the semiconductor die level. Circuits are also disclosed and claimed which provide for some of the LEDs in a circuit to be on during both positive and negative phases of an AC source, to among other things, address flicker. Also, circuits are claimed and disclosed where a basic circuit design provides a voltage and current performance whereby scalability or matching a particular voltage requirement is achieved by configuring LEDs in the basic design and/or by joining one or more of the basic circuits together in series or basic to achieve the design requirement. 
     According to an embodiment of the invention an AC-driven LED circuit is proposed having at least a first [basic] circuit comprising LEDs. Each LED has an input and an output, and the circuit having at least first and second basic branches connecting at first and second common points, the common points providing input and output for an AC driving current for the circuit. This circuit as well as others described and claimed herein incorporating various numbers of LEDs may be referred to herein as a “circuit module,” a “basic LED circuit,” or a “subcircuit,” given the fact that according to an aspect of the invention such circuits themselves may be joined with other such circuits in either basic or series relationships to each other. The first branch of the basic LED circuit has a first and a second LED, and the second branch having a third and a fourth LED. The first LED is connected to the second LED in opposing series relationship with the inputs of the first and second LEDs defining a first branch junction. The third LED is connected to the fourth LED in opposing series with the outputs of the third and fourth LEDs defining a second branch junction. The first and second branches are connected to one another such that the output of the first LED is connected to the input of the third LED at the first common point and the output of the second LED is connected to the input of the fourth LED at the second common point. At least one (or a first) cross-connecting circuit branch having at least a fifth LED is provided in an embodiment of the invention, the first cross-connecting circuit being configured such that the input of the fifth LED is connected to second branch junction and its output is connected to the first branch junction. It is important to note that according to an embodiment and aspect of the invention that circuits disclosed and claimed herein, result in an antibasic relationship of certain LEDs and further resulting in an imbalanced bridge effect in operation. 
     An AC LED bridge is an LED topology where the self rectifying property of anti basic LED strings is used to drive a set of ‘bridge’ LEDs with rectified current. An imbalanced bridge is the general implementation of this topology where one side of the input to the bridge has a different number of LEDs in series than the other side. A balanced bridge is a particular implementation of this topology where the input and output sides have equal numbers of LEDs in series. When used in a specific voltage drive regime, such as 12V AC, the advantage of an imbalanced bridge topology is that it can be constructed for example with standard GaN die so that the forward combined voltage of the die in one phase cycle is closely matched to the native supply voltage while the reverse voltage applied to the diodes in the opposing phase is kept to an acceptable level blow the reverse breakdown voltage of the die. 
     According to another embodiment of the invention, an AC-driven LED circuit may comprise one or more additional basic circuits each being the same as the first basic circuit identified above. Each additional circuit being conductively connected to the first basic circuit and to one another at the their common points for providing an input and an output for an AC driving current of the circuit. According to other embodiments, the additional basic circuits may be connected in series to the first basic circuit and to one another or the additional basic circuits may be connected in basic to the first basic circuit and to one another. 
     According to another embodiment of the invention, n additional LEDs, in pairs, may be provided in the circuit wherein the pairs are configured among the first and second branch circuits of each of the respective basic circuits or modules, such that current flows through the respective fifth diode of each basic circuit upon both a negative and positive phase of the AC driving source and so that the current draw through each of the respective basic circuits during both AC phases is substantially the same. 
     According to another embodiment the AC-driven LED circuit further comprises x cross-connecting circuit branches each having one or more LEDs and being configured such that current flows through each of the respective one or more LEDS upon both a negative and positive phase of the AC driving source and so that the current draw through each of the respective basic circuits during both AC phases is substantially the same. 
     According to an embodiments and aspect of the invention, the basic LED circuit and more complex circuits derived therefrom include a one or more of a resistor, a transient or surge protector, and a microfuse; in any number or combination respecting the needed or desired impedence, resistance, and/or drive current/voltage protection. 
     According to another aspect and embodiment of the invention, the circuit embodiments described and claimed herein are formed on a single semiconductor chip. Another embodiment and aspect of the invention provides that the circuits described and claimed herein including the LED die are formed on a sapphire substrate. 
     According to another embodiment of the invention, an AC-driven LED assembly comprises at least a first and a second LED each discretely packaged, the LEDs being connected in an AC circuit and each LED package being mounted to a substrate at a distance from the other of preferably approximately 3 mm or less, and more preferably 2.0 mm or less. In an embodiment the packaged LEDs also each have a length of preferably approximately 2.5 mm or less, and more preferably 2.0 mm or less. In an embodiment the packaged LEDs also each have a width of preferably approximately 2.5 mm or less, and more preferably 2.0 mm or less. In an embodiment the LED packages are arranged with respect to each other in a linear spatial relationship while in another embodiment the LED packages are arranged with respect to each other in an XY rectilinear spatial relationship. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an AC-driven LED circuit according to an embodiment of the invention; 
         FIG. 2  is a schematic view of an AC-driven LED circuit according to an embodiment of the invention; 
         FIG. 3  is a schematic view of an AC-driven LED circuit according to an embodiment of the invention; 
         FIG. 4  is a schematic view of an AC-driven LED circuit according to an embodiment of the invention; 
         FIG. 5  is a schematic view of an AC-driven LED circuit according to an embodiment of the invention; 
         FIG. 6  is a schematic top view of an AC-driven LED assembly according to an embodiment of the invention; 
         FIG. 7  is a schematic top view of an AC-driven LED assembly according to an embodiment of the invention; and, 
         FIG. 8  is a schematic side view of an AC-driven LED assembly according to an embodiment of the invention. 
         FIG. 9  is a schematic view of a modification to AC-driven circuit  70  of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     While this invention is susceptible to embodiments in many different forms, there are shown in the drawings and will herein be described in detail, preferred embodiments of the invention with the understanding that the present disclosures are to be considered as exemplifications of the principles of the invention and are not intended to limit the broad aspects of the invention to the embodiments illustrated. Like components in the various FIGS. will be given like reference numbers. 
       FIG. 1  discloses an AC-driven LED circuit  10  including a first basic circuit  12  having a first branch  14 , and a second branch  16 . Branches  14 ,  16  connect at first common point  18  and second common point  20 . The common points  18 ,  20  provide input and output for an AC driving current from a driver  24  for the circuit. 
     The first branch  14  has a first LED  26  and a second LED  28 , and the second branch  16  having a third LED  30  and a fourth LED  32 . The first LED  26  is connected to the second LED  28  in opposing series relationship with the inputs of the first and second LEDs  26 ,  28  defining a first branch junction  34 . The third LED  30  is connected to the fourth LED  32  in opposing series with the outputs of the third and fourth LEDs  30 ,  32  defining a second branch junction  36 . 
     The first and second branches  34 ,  36  are connected to one another such that the output of the first LED  26  is connected to the input of the third LED  30  at the first common point  18  and the output of the second LED  28  is connected to the input of the fourth LED  32  at the second common point  20 . A first cross-connecting circuit branch  38  has a fifth LED  40 . The first cross-connecting circuit branch  38  being configured such that the input of the fifth LED  40  is connected to second branch junction  36  and the output is connected to the first branch junction  34 . 
     As will be appreciated by those of skill in the art, the LED&#39;s  26  and  32  will provide light only upon one half of an AC wave, pulse or phase, while LEDs  28  and  30  will provide light only upon the opposite wave, pulse or phase. At lower frequencies, e.g. mains frequencies, if the LEDs are spaced pursuant to another aspect of the invention (disclosed below) at preferably approximately 3.0 mm or less preferably approximately 2.0 mm or less, then the amount of noticeable flicker may not be unacceptable. However, the cross connecting circuit  38  and diode  40  will be on (produce light) in both phases of the AC drive and hence mitigate flicker which may be evidenced in its surrounding LEDs  26 ,  28 ,  30  and  32 . 
     Advantageously the LED circuit  10  provides an LED topology an imbalanced bridge effect as one side of the circuit has a different number of LEDs in series than the other side. This characteristic is also disclosed in all of the circuits in  FIGS. 1-9 . 
       FIG. 2  discloses an AC-driven LED circuit  50  which is a modification of AC-driven LED circuit  10 . Circuit  50  further mitigates flicker. Circuit  50  provides an additional cross-connecting circuit branch  42  having LED  44 . The LEDS  40 ,  44  are configured such that current flows through each upon both a negative and positive phase of the AC driving source  24 . It should be appreciated that according to the invention x number of such cross connecting circuit branches (such as  38 ,  42 ) may be added as desired, however, since the LEDs (such as LEDs  40 ,  44 ) are in basic with each other, their voltage demand will be divided while their current draw will not. Hence a suitable driver need be provided for this circumstance. 
     To increase the light output of the circuit of the invention, it should be noted as disclosed in  FIG. 3  that additional or n LEDS may be provided in the branches  14  and  16 . Specifically  FIG. 3  discloses an AC-driven circuit  60  which is a modification of circuit  50 . Circuit  60  provides for additional LEDs  46  and  48 . The pair of LEDs are configured among the first and second branch circuits  14 ,  16  of the basic circuit  15  such that current flows through the respective diodes  40 ,  44  upon both a negative and positive phase of the AC driving source  24  and so that the current draw through basic circuit  15  during both AC phases is substantially the same. 
     It should be noted that according to the invention, n pairs of LEDs can be configured among first and second branch circuits of a respective basic circuit, such that current flows through the respective cross connecting circuit branch LEDs of a basic circuit upon both a negative and positive phase of the AC driving source and so that the current draw through each of the respective basic circuits during both AC phases is substantially the same. More LEDs in the branch circuits divide the current from the higher current LEDs in cross connecting circuits  38 ,  42 . 
     According to another aspect of the invention, to further mitigate the amount of flicker perceived, adding to the light provided and to scalability, additional basic circuits, each being the same as the first basic circuit, may be conductively connected to the first basic circuit in series or basic at the their common points  18 ,  20  for providing an input and an output for an AC driving current for the circuit. 
     For instance,  FIG. 4  discloses an AC-driven LED circuit  70  which includes additional basic circuits  15  connected in series at common points  18 ,  20 . Additionally, as seen in  FIG. 5 , an AC-driven LED circuit  80  includes additional basic circuits  15  connected in basic at common points  18 ,  20 . This embodiment shows the utility of providing a scalable circuit that can be manufactured modularly and used to connect to match higher voltage requirements e.g. circuit  15  may draw drawing 12 V AC while two such circuits  15  in series would meet 24V AC requirements. 
     Preferably, the number and type of LEDs in the AC-driven LED circuit draws a combined current and combined voltage which is substantially equal to the nominal voltage capacity of the AC drive source. 
     As shown in  FIG. 6 , an AC-driven LED assembly  90  has a first and a second LED  82  each discretely packaged, the LEDs being connected in an AC circuit and each LED package  82  being mounted to a substrate  92  at a distance d 1  from the other of preferably approximately 3 mm or less, and more preferably 2.0 mm or less. The AC-driven LED assembly  90  also has packaged LEDs  84  each having a width d 2  and a length d 3  of preferably approximately 2.5 mm or less, and more preferably 2.0 mm or less. 
       FIG. 6  discloses an AC-driven LED assembly  90  wherein the LED packages  84  are arranged with respect to each other in a linear spatial relationship, while  FIG. 7  discloses an assembly  100  wherein the LED packages  84  are arranged with respect to each other in an XY rectilinear spatial relationship. 
     As can be seen in  FIG. 8 , when LED packages  84  are placed at 3 mm or less, the light produced therefrom intersects, thereby reducing or eliminating the effects of flicker. 
       FIG. 9  discloses a modification to AC-driven circuit  70  which according to the invention, whether embodied on a single chip, or to other another substrate or circuit board mounting, is provided with one or more at the option of the design criteria, to include one or more of a transient voltage suppressor  45  or like device, a micro-fuse  47 , or like device (e.g. a PTC device) and a resistor  49 . The resistor  49  may be unnecessary in a design where the resistance/impedance of the fusing and/or overvoltage devices are sufficient for the circuit performance. 
     According to the invention, the various embodiments of the basic LED circuits and larger circuits of serial and parallel arrangements of same are formed by forming the die/and or other circuit elements on a single semiconductor chip or a substrate, or mounted to substrates, and assemblies may be produced, such as creating an AC-driven circuit where all circuits and LEDs are formed on a semiconductor, where the LED are discretely packaged apart from the circuits, and where each basic circuit is formed on a printed circuit board. Preferably according to an aspect of the invention the basic circuits and larger circuits combining them may be formed on a sapphire substrate for thermal management of the numerous LED die. 
     While in the preceding there has been set forth a preferred embodiment of the invention, it is to be understood that the present invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. While specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the characteristics of the invention and the scope of protection is only limited by the scope of the accompanying Claims.