Patent Publication Number: US-11378238-B2

Title: Light string and light string circuits

Description:
PRIORITY CLAIM 
     This application is a continuation of U.S. patent application Ser. No. 16/874,848, filed May 15, 2020, which is a continuation of U.S. patent application Ser. No. 16/219,657, filed Dec. 13, 2018, which claims the benefit of U.S. Provisional Patent Application No. 62/598,288, filed Dec. 13, 2017, the contents of which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The instant disclosure relates to decorative light strings, and in particular, relates to light strings, circuits of light strings, and methods of manufacturing light strings. 
     BACKGROUND OF THE INVENTION 
     A light string that includes plural light sources directly soldered onto electric conductors at intervals, so as to form a string-shaped illumination device without a lamp holder, is known in the art. An example of such a light string is found in U.S. Pat. No. 8,397,381, entitled Method of Manufacturing Light Set with Surface Mounted Light Emitting Components. Light strings having many small-sized light sources, such as small bulbs that include light emitting diodes (LEDs), are commonly known. A light string is as flexible as the electric wire is, such that the light string is easily arranged in any configuration to comply with requirements for special illumination or decoration. 
     In the art, light sources are soldered to the copper core or conductor after the insulating layer of the electric wire or wire is removed, and then an electrical insulating treatment is performed on the solder joints. In this approach, light sources obviously stick out on the electric wire and are configured to have high-directivity. When arranging a light string, which may include pulling the light string, the light sources may be subject to forces and shocks that result in solder joints cracking. Furthermore, usually electric wires are flexible, but the soldering material is not as flexible. Thus, when the electric wire of the light string is pulled or bent, stress concentration often occurs at the soldering joints and results in soldering joints cracking. 
     In addition, in a light string, light sources are typically electrically connected in series or electrically connected in parallel. In parallel, precise driving voltage is required to drive the light source and prevent the light sources from being damaged by over-current. In a series connection, the number of the light sources is determined by the output voltage of the power source, with the number and type of light source being selected to ensure that every light source is driven by an appropriate voltage with an allowable voltage difference. This means that the number of the light sources is restricted by the output of the power source such that the number cannot be changed at will. Meanwhile, one damaged light can result in failure of the whole light string. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides embodiments of light strings, systems and circuits thereof, as well as methods of manufacturing light strings, that present an improvement over known light strings and related systems, circuits, and methods of manufacturing. 
     According to an embodiment of the present disclosure, a light string includes at least one illumination device, a first wire and a second wire. 
     The illumination device includes a substrate and a light source; wherein the substrate includes a carrier portion and two soldering portions, the carrier portion is located between the two soldering portions, and the light source is disposed on the carrier portion. The first wire includes a first conductor, which may comprise one or more conductive strands, and a first insulating layer; wherein the first insulating layer wraps around the first conductor and the first conductor is partially exposed to form at least one first soldering section. The second wire includes a second conductor and a second insulating layer; wherein the second insulating layer wraps around the second conductor, and the second conductor is partially exposed to form at least one second soldering section. The first soldering section and the second soldering section are attached to the two soldering portions of the substrate respectively; and the light source is located between the first soldering section and the second soldering section. The soldering material is disposed onto the two soldering portions and at least partially covers the first soldering section and the second soldering section, so as to attach the first soldering section and the second soldering section to the two soldering portions respectively. In an embodiment, a transparent covering, such as an adhesive, which may be glue, covers the illumination device, the first soldering section and the second soldering section, and extends to partially cover the first insulating layer and the second insulating layer. In an embodiment, the transparent glue has a largest cross-sectional area in an area corresponding to the light source, and the cross-sectional area of the transparent glue shrinks gradually along a direction toward the first insulating layer and the second insulating layer. 
     According to another embodiment of the present disclosure, a circuit of light string includes a first wire, a second wire, and a plurality of illumination devices. 
     Each of the illumination devices includes a substrate and a light source. The substrate includes a carrier portion, an anode soldering portion and a cathode soldering portion, the carrier portion is located between the anode soldering portion and the cathode soldering portion, and the light source is disposed on the carrier portion and electrically connected to the anode soldering portion and the cathode soldering portion. The illumination devices are electrically connected to the first wire and the second wire by the anode soldering portions and the cathode soldering portions. 
     According to yet another embodiment of the present disclosure, a circuit of a light string includes a first wire, a second wire, a plurality of illumination devices, and a third wire. 
     In an embodiment, each of the illumination devices includes a substrate, a light source and a controller; wherein the substrate includes a carrier portion, an anode soldering portion and a cathode soldering portion, the carrier portion is located between the anode soldering portion and the cathode soldering portion, and the light source is disposed on the carrier portion, and electrically connected to the anode soldering portion and the cathode soldering portion; the controller is combined with the substrate for enabling and disabling the light source, and the controller includes a signal-input terminal and a signal-output terminal; and each of the illumination devices are electrically connected to the first wire by the anode soldering portions, and electrically connected to the second wire by the cathode soldering portions. The third wire includes a signal-input end and a signal-output end, and a plurality of cut-off points are arranged on the third wire. Each of the illumination devices is disposed at one of the cut-off points respectively, and the signal input terminal and the signal output terminal are electrically connected to the third wire respectively via different sides of the corresponding cut-off point. The third wire receives a control signal from the signal input end, and transfers the control signal to each of the controllers via the signal input terminals to control the corresponding light source, and the control signal is transferred to the controller of the next illumination device via the signal output terminals. 
     In the present disclosure, the illumination devices are securely soldered between the first wire and the second wire, and provide good illumination effect. Moreover, embodiments of circuits of light strings in the present disclosure provide a variety of approaches to supplying power, adopt various types of light source, and ensure that every light source can receives acceptable power input to prevent under voltage resulting from too many light sources. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus not limitative of the present invention, wherein: 
         FIG. 1  is an exploded view of a first wire, a second wire and an illumination device, according to a first embodiment of the present disclosure; 
         FIG. 2  is a three-dimensional view of the first wire, the second wire and the illumination device combined together, according to the first embodiment of the present disclosure; 
         FIG. 3  is a three-dimensional view of a light string, according to the first embodiment of the present disclosure; 
         FIG. 4  is a cross-sectional view of the first wire, the second wire and the illumination device combined together according to the first embodiment of the present disclosure; 
         FIG. 5  is a cross-sectional view of the light string according to the first embodiment of the present disclosure; 
         FIG. 6  is a circuit diagram of a circuit of light string according to a second embodiment of the present disclosure; 
         FIG. 6A  is a depiction of a light string having the circuit of  FIG. 6 , according to an embodiment of the present disclosure; 
         FIG. 6B  is a simplified cross-sectional view of the light string of  FIG. 6A ; 
         FIG. 7  and  FIG. 8  are circuit diagrams of a circuit of light string according to a third embodiment of the present disclosure; 
         FIG. 9  is a circuit diagram of a circuit of light string according to a fourth embodiment of the present disclosure; 
         FIG. 9A  is a depiction of a light string having the circuit of  FIG. 9 , according to an embodiment of the present disclosure; 
         FIG. 9B  is a view of a portion of the light string of  FIG. 9A , according to an embodiment of the present disclosure; 
         FIG. 10  and  FIG. 11  are circuit diagrams of a circuit of a light string according to a fifth embodiment of the present disclosure; and 
         FIG. 12  is a top view of an illumination device according to the fifth embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 ,  FIG. 2  and  FIG. 3 , a light string  100  includes one or more illumination devices  130 , a first wire  110 , a second wire  120 , soldering material  140  and transparent adhesive  150 . 
     Referring to  FIGS. 1-4 , although only one illumination device  130  is illustrated in the drawings, the light string  100  in the present disclosure can be equipped with two or more than two illumination devices  130  and disposed between the first wire  110  and the second wire  120  in parallel. Each of the illumination devices  130  includes a substrate  131  and a light source  132 . The substrate  131  includes a carrier portion  133  and two soldering portions  134 . The carrier portion  133  is located between the two soldering portions  134 , and the light source  132  is disposed on the carrier portion  133 . 
     At least the surface of each of the soldering portions  134  is comprised of a conductive material  135  and respectively connected to the light source  132 . In one example, a metal layer is plated on each of the soldering portions  134 , to serves as the conductive material  135 . In another example, each of the soldering portions  134  is made of metal, and the substrate  131  is formed by joining the insulation part (the carrier portion  133 ) and the conductive part (the soldering portions  134 ). 
     Referring to  FIG. 4 , the light source  132  further includes a light-emitting component  136  and a transparent package body  137 . The light-emitting component  136  is disposed on the carrier portion  133  of the substrate  131 , and the transparent package body  137  covers the light-emitting component  136 . 
     In one example, the illumination device  130  is a surface-mount technology light-emitting diode (SMT LED). The light-emitting component  136  is a light-emitting diode chip. The substrate  131 , in an embodiment, is a sapphire substrate. The transparent package body  137 , in an embodiment, is composed of solidified glue or adhesive, wherein liquid glue is dispensed on the light-emitting diode chip and solidified to form the transparent package body  137 . A convex portion is formed on the upper surface of the transparent package body  137  to increase the beam angle and the brightness of illumination. In an embodiment, the liquid glue is a resin encapsulation glue containing phosphor, and the proportion of phosphor to the rest of the liquid glue determines the fluidity of the liquid glue and the curvature of the convex. 
     Referring to  FIG. 1 ,  FIG. 2  and  FIG. 4 , the first wire  110  includes a first conductor  112  and a first insulating layer  114 . In an embodiment, conductor  112  comprises a single strand conductor, and in other embodiments, comprises multiple strands, which may be twisted about one another. The first insulating layer  114  wraps around the first conductor  112 , and the first conductor  112  is partially exposed to form at least one first soldering section  116 . During a manufacturing process, first soldering section  112  and second soldering section  116  may be formed in a variety of ways. In an embodiment, an axial (lengthwise) pull force or tension is applied to wires  100  and  120 , then a portion of insulating layers  114  and  124  are cut, in some cases circumferentially, without cutting the conductors, causing portions of the insulating layers  114  and  124  to move axially along the respective conductors, exposing a portion of the conductors of the wires, thereby creating first soldering section  112  and second soldering section  116 . In an embodiment, the number of first soldering sections  116  is equal to the number of the illumination devices  130 . 
     As shown in  FIG. 1 ,  FIG. 2  and  FIG. 4 , the second wire  120  includes a second conductor  122  and a second insulating layer  124 . The second insulating layer  124  wraps around the second conductor  122 , and the second conductor  122  is partially exposed to form at least one second soldering section  126 . In an embodiment, the number of second soldering sections  126  is equal to the number of illumination devices  130 , and each first soldering section  116  is paired with a second soldering section  126 . 
     In an embodiment, and as shown in  FIG. 2  and  FIG. 4 , the first soldering section  116  and the second soldering section  126  are attached to the two soldering portions  131  of the substrate  134  respectively, and the light source  132  is disposed between the first soldering section  116  and the second soldering section  126 , such that the first soldering section  116  and the second soldering section  126  hold the illumination device  130  and its light source  132  in a clamping manner. In such an embodiment, wires  110  and  120  impart a retaining force in a direction perpendicular to a lengthwise axis of the wires, on illumination devices  130 , which aids in retaining each illumination device  130  in contact with soldering sections  116  and  126 . 
     As shown in the drawings, the soldering material  140  is disposed onto the two soldering portions  134  and partially covers the first soldering section and the second soldering section, to attach the first soldering section  116  and the second soldering section  126  to the two soldering portions  134  respectively. In an embodiment, to prevent solder joints on the first soldering section  116  and the second soldering section  126  from cracking, the soldering material  140  further extends to cover a lateral edge and a back surface of the substrate  131 , and surfaces of the lateral edge and the back surface are comprised of the conductive material  135  as well. Such a method of soldering causes conductive joining of a greater conductive area of the soldering sections of the conductors of the wire, and a larger conductive area of the soldering portions of the illumination device. The result is a stronger mechanical bond, which results in a higher quality, more durable light set, and also avoids known non-wetting issues that may arise in solder joints accomplished by other manufacturing methods. 
     As shown in  FIG. 1  and  FIG. 2 , in an embodiment, the transparent adhesive or glue layer  150  covers the illumination device  130 , the first soldering section  116  and the second soldering section  126 , and further extends to partially cover the first insulating layer  114  and the second insulating layer  124 . The transparent glue  150  has a largest cross-sectional area at a location corresponding to the light source  132 . 
     The cross-sectional area of the transparent glue  150  shrinks gradually along directions toward the first insulating layer  114  and the second insulating layer  124 . That is, the transparent glue bulk  150  not only covers the illumination device  130 , the first soldering section  116  and the second soldering section  126 , but also covers the sections of the first second insulating layer  114  and the second insulating layer  124  which are adjacent to the transparent glue layer  150 . 
     The material of the transparent adhesive  150  can comprise rapid solidification glue such as a UV cure adhesive. During manufacture, liquid glue is dispensed onto the light source  132  by a glue dispenser, and then the liquid glue flows over the top of the light source  132  and into the adjacent sections of the first insulating layer  114  and second insulating layer  124 . 
     Referring  FIG. 4 , the transparent glue  150  extends to partially cover the first insulating layer  114  and the second insulating layer  124 . In an embodiment, the transparent glue  150  when solidified is tough and may have a hardness higher than a hardness of any portion of the first wire  110  or the second wire  120 . Therefore, when the first wire  110  or the second wire  120  is bent for arrange the light string  100 , the section of the first wire  110  or the second wire  120  equipped with the illumination device  130  will not be bent, so as to prevent solder joints on the first soldering section  116  or the second soldering section  126  from cracking due to bending stress. Moreover, the transparent glue layer  150  also serves as a light guide device, so as to significantly increase the beam angle of the light source  132 . 
     Referring to  FIG. 5 , when the first wire  110  and the second wire  120  are pulled, the first soldering section  116  and the second soldering section  126  press against the illumination device  130  with only minimal shear stress between the soldering portions  134  and the first soldering section  116  or between the soldering portions  134  and the second soldering section  126 . Therefore, the light string  100  also prevents solder joints on the first soldering section  116  or the second soldering section  126  from cracking due to shear stress. 
     That is, the coverage of the transparent glue layer  150  strengthens the light string  100  to withstand bending stress, and the arrangement of the first soldering section  116 , the second soldering section  126  and the illumination device  130  strengthens the light string  100  to withstand shear stress. 
     In an embodiment, the first conductor  112  and/or the second conductor  122  may be solid, single-strand conductors (single piece copper conductor or metal conductor made of an appropriate conductive metal, such as copper, a copper alloy, and so on) as is depicted in  FIG. 1  to  FIG. 5 . Alternatively, the first conductor  112  and/or the second conducting wire  122  may comprise stranded conductors instead of a single piece conductor. In the first embodiment, the first second insulating layer  114  and the second insulating layer  124  are respectively plastic insulators, such as polyvinylchloride (PVC). In one or more embodiments, the first insulating layer  114  and the second insulating layer  124  are very thin layers of insulation, such as an enamel coating, such that the first wire  110  or the second wire  120  are enameled wires. In one or more embodiments, the first insulating layer  114  and the second insulating layer  124  are combined into one piece for convenience of wire arrangement. 
     Referring to  FIGS. 6, 6A and 6B , features of a 3-wire light string  100  and circuit  2  are depicted.  FIG. 6  depicts an electrical schematic of a circuit  2 ;  FIG. 6A  depicts an embodiment of a 3-wire light string  100 ; and  FIG. 6B  depicts a simplified cross-sectional view of light string  100 . Although  FIG. 6B  depicts an embodiment of illumination device  130  positioned on top of conductors  112 ,  116  and  162  for the sake of illustrating the basic electrical connections of illumination device  130  with wires  110 ,  120  and  160 , it will be understood that other embodiments of light string  100  are consistent with the previous description and depictions of illumination device  130  being attached “below” or between the respective conductors. 
     Referring to  FIG. 6 , a circuit  2  of the light string  100  is depicted according to a second embodiment of the present disclosure. In the embodiment of  FIG. 6 , multiple illumination devices  130  are arranged in series and parallel on three wires to form light string  100 . 
     As depicted in  FIGS. 6, 6A and 6B , the circuit  2  in the second embodiment includes a first wire  110 , a second wire  120 , a third wire  160  and a plurality of illumination devices  130 . Third wire  160  includes conductor  162  and insulation layer  164 . 
     The first wire  110  is used to receive a first electric potential V 1 ; and in one example, the first electric potential is 6V direct current (DC). The third wire  160  is used to receive a third electric potential V 3 ; and in one example the third electric potential V 3  is ground potential (GND). The second wire  120  is used as a connection node among the illumination devices  130 . 
     In an embodiment, each of the illumination devices  130  is substantially identical to the illumination device  130  in the first embodiment. In the second embodiment, the soldering portions  134  of each illumination device  130  are sorted into an anode soldering portion (+) and a cathode soldering portion (−) according to the polarity of the light source  132  (in particular to the LED polarity). The carrier portion  133  as described in the first embodiment is located between the anode soldering portion (+) and the cathode soldering portion (−) and the light source  132  is disposed on the carrier portion  133  and electrically connected to the anode soldering portion (+) and the cathode soldering portion (−). 
     As depicted in  FIG. 6 , some of the illumination devices  130  are electrically connected to the first wire  110  at the anode soldering portions (+) and electrically connected to the second wire  120  at the cathode soldering portions (−). The other illumination devices  130  are electrically connected to the second wire  120  at the anode soldering portions (+) and electrically connected to the third wire  160  at the cathode soldering portions (−). 
     Therefore, the illumination devices  130  are sorted into two groups. In the first group, the illumination devices  130  are electrically connected in parallel by connection to the first wire  110  and the second wire  120  respectively. In the second group, the illumination devices  130  are electrically connected in parallel by connected to the second wire  120  and the third wire  130  respectively. 
     The first group is electrically connected to the second group in series via the second wire  120 . 
     As shown in  FIG. 6 , in an embodiment, the circuit  2  further includes a current-limiting resistor  180 , electrically connecting the first electric potential V 1  to the first wire  110  for limiting current in the first wire  110 . The current-limiting resistor  180  limits the current in the first wire  110 , so as to prevent the illumination devices  130  from being damaged by over-current. In an embodiment, a section of a conductor of the wire is cut out, or the conductor is otherwise cut or interrupted, and a resistor may be soldered between the two resulting ends of the conductor. 
     In the second embodiment, the first wire  110 , the second wire  120  and the third wire  130  are arranged in parallel. In one such embodiment, the insulating layers of the first wire  110 , the second wire  120  and the third wire  160  can be combined together into a unitary layer and only the sections of the wires on which the illumination devices  130  are disposed need have insulation removed. Therefore, the circuit  2  becomes a long single-piece light string for convenience of wires arrangement. 
     Referring to  FIG. 7  and  FIG. 8 , a circuit  3  of the light string according to a third embodiment includes a first wire  110 , a second wire  120 , a third wire  160  and a plurality of illumination devices  130 . The circuit  3  further includes a third cut-off point C 3 , a second cut-off point C 2  and a first cut-point C 1  to form the circuit loop in the third embodiment. Cut-off points are points along a length of the wire wherein the conductor is “broken” or interrupted, such that the conductor of the wire is not contiguous. In an embodiment, a portion of the conductor is removed to achieve a discontinuity; in other embodiments, the conductor is simply cut. In the latter embodiment, lengthwise tension on the conductor may cause a gap between ends of the conductor, or alternatively, portions of the conductor may be bent away from one another to form a gap. 
     As shown in  FIG. 7 , the first wire  110 , the second wire  120  and the third wire  130  are arranged in parallel to an extension direction L; in one embodiment, the three wires are single metal wires or stranded conductors combined together by a one-piece insulating layer. The one-piece insulating layer may comprise a uniform or non-uniform layer thickness. In an embodiment, a portion of a think connecting layer joins any two conductors together. 
     The third cut-off point C 3 , the second cut-off point C 2  and the first cut-point C 1  are arranged sequentially along the extension direction L, respectively breaking conductive continuity of the third wire  160 , the second wire  120  and the first wire  110  so as to divide the circuit  3  into a plural of sections based on the third cut-off point C 3 , the second cut-off point C 2  and the first cut-off point C 1 . 
     In an embodiment of  FIG. 7 , each of the illumination devices  130  is substantially identical to the illumination device  130  in the first embodiment or the second embodiment. Each of the illumination devices  130  includes a substrate  131  and a light source  132 . The substrate  131  includes a carrier portion  133 , an anode soldering portion (+) and a cathode soldering portion (−). The carrier portion  133  is located between the anode soldering portion (+) and the cathode soldering portion (−). The light source  132  is disposed on the carrier portion  133 , and electrically connected to the anode soldering portion (+) and the cathode soldering portion (−). 
     Referring to  FIG. 8 , the illumination devices  130  are sorted into groups. The first group of the illumination devices  130  are arranged before the first cut-off point C 1  along the extension direction L, which is a longitudinal direction, (starting from the left side of  FIG. 8 ), electrically connected to the first wire  110  by the anode soldering portions (+), and electrically connected to the second wire  120  by the cathode soldering portions (−). First wire  110  defines a first end  110   a  and a second end  110   b , a first wire segment  110   c  and a second wire segment  110   d ; second wire  120  defines a first end  120   a  and a second end  120   b , a first wire segment  120   c  and a second wire segment  120   d ; and third wire  160  defines a first end  160   a  and a second end  160   b , a first wire segment  160   c  and a second wire segment  160   d.    
     Referring to  FIG. 8 , the second group of the illumination devices  130  are arranged between the third cut-off point C 3  and the second cut-off point C 2  along the extension direction L, electrically connected to the second wire  120  by the anode soldering portions (+), and electrically connected to the third wire  160  by the cathode soldering portions (−). 
     Referring to  FIG. 8 , the third group of the illumination devices  130  are arranged after the second cut-off point C 2  along the extension direction L, electrically connected to the second wire  120  by the cathode soldering portions (−), and electrically connected to the third wire  160  by the anode soldering portions (+). 
     The fourth group or the rest of the illumination devices  130  are arranged after the first cut-off point C 1  and the second cut-off point C 2  along the extension direction L electrically connected to the first wire  110  by the cathode soldering portions (−), and are electrically connected to the second wire  120  by the anode soldering portions (+). 
     With such an approach, the illumination devices  130  are sorted into four groups. In the first group, the illumination devices  130  are electrically connected in parallel by connected to the first wire  110  and the second wire  120  respectively. In the second group, the illumination devices  130  are electrically connected in parallel by connection to the second wire  120  and the third wire  130  respectively. 
     Meanwhile, the first group is electrically connected to the second group in serial via the second wire  120 . 
     In the third group, the illumination devices  130  are electrically connected in parallel by connection to the second wire  120  and the third wire  130  respectively. 
     The polarity of the third group is opposite to the second group, and the second wire  120  between the second group and the third group is cut off by the second cut-off point C 2 . Therefore, the third group of illumination devices  130  is serially connected to the second group of illumination devices  130 . Similarly, in the fourth group, the illumination devices  130  are electrically connected in parallel by connection to the first wire  110  and the second wire  120  respectively. The polarity of the fourth group is opposite to the first group, and the first wire  120  between the first group and the fourth group is cut off by the first cut-off point C 1 . Therefore, the fourth group of illumination devices  130  is serially connected to the third group of illumination devices  130 . 
     Still referring to  FIG. 8 , one end of the first wire  110  receives a first electric potential V 1 ; and in one example, the first electric potential is an alternating current (AC) voltage, such as 110V or 220V. In an embodiment, the other end of the first wire  110  is electrically connected to a boost line  170 . A boost potential V 4  is provided by the boost line  170  according to the electric potential of the first wire  110  and required drive voltage for driving the four groups of illumination devices  130 , so as to boost the voltage applied to each illumination device  130 . Generally, the longer the wire, the greater the power consumed by the LEDs, and the greater the potential to have an overall voltage drop delivered to the LEDs furthest from the connection point of the power source. Such a situation can cause some illumination devices  130  to receive a lower voltage than other devices  130 , causing a disparity in light output. A solution according to an embodiment is to connect a boost line  170  as described herein. 
     Similarly, in the third embodiment, the first wire  110 , the second wire  120 , the third wire  130  and the boost line  170  are arranged in parallel, the circuit  3  becomes a long single piece light string for convenience of wires arrangement. 
     Still referring to  FIG. 8 , in an embodiment, the circuit  3  further includes a current-limiting resistor  180 , electrically connecting the first electric potential V 1  to the first wire  110  for limiting current in the first wire  110 . The current-limiting resistor  180  limits the current in the first wire  110 , so as to prevent the illumination devices  130  from being damaged by over-current. Alternatively, the current-limiting resistor  180  is disposed on the boost line  170 , which is also located on the serial current loop to limit the current thereon. 
     Referring to  FIGS. 9, 9A and 9B , a circuit  4  of the light string is shown according to a fourth embodiment of the present disclosure. 
     The circuit  4  includes a first wire  110 , a second wire  120 , a boost line  170  and a plurality of illumination devices  130 . 
     The first wire  110  is used to receive a first electric potential V 1 ; and in an embodiment, the first electric potential is 3V direct current (DC). The second wire provides a second electric potential V 2  and in one example the second electric potential V 2  is ground potential (GND). And the boost line  170  receives a boost potential V 4 . 
     Similar to the first embodiment, each of the illumination devices  130  includes a substrate  131  and a light source  132 . The substrate  131  includes a carrier portion  133 , an anode soldering portion (+) and a cathode soldering portion (−). The carrier portion  133  is located between the anode soldering portion (+) and the cathode soldering portion (−). The light source  132  is disposed on the carrier portion  133 . The detailed description of each illumination device  130  is described in the first embodiment. In the fourth embodiment, each of the illumination devices  130  are electrically connected to the first wire  110  by the anode soldering portions (+) and electrically connected to the second wire  120  by the cathode soldering portions (−). The boost line  170  is electrically connected to the second wire  120 . 
     By such an approach, the illumination devices  130  are electrically connected in parallel between the first wire  110  and the second wire  120 , and the illumination devices  130  are normally driven by the voltage difference between the first wire  110  and the second wire  120 . A boost potential V 4  is provided by the boost line  170  according to the electric potential of the first wire  110  and required drive voltage for driving the illumination devices  130 , so as to boost the voltage applied to each illumination device  130 . 
     Similarly, in the fourth embodiment, the first wire  110 , the second wire  120  and the boost line  170  are arranged in parallel, the circuit  3  becomes a long single-piece light string based on the convenient joined-wire arrangement. 
     In an embodiment, boost line  170  is electrically connected to wire  120 . In one such embodiment, and also referring to  FIG. 9B , boost line  170  comprises a portion of wire  120  that is bent at bend  180 , such that wire  120  extends away from a power source, then back towards the power source. In another embodiment, boost line  170  comprises a separate and distinct wire that is electrically connected to wire  120 . 
     In an embodiment, the circuit  4  further includes a current-limiting resistor  180 , electrically connecting the first electric potential V 1  to the first wire  110  for limiting current in the first wire  110 . The current-limiting resistor  180  limits the current in the first wire  110 , so as to prevent the illumination devices  130  from being damaged by over-current. Alternatively, the current-limiting resistor  180  is disposed on the boost line  170 , which is also located on the serial current loop to limit the current thereon. 
     Referring to  FIG. 10  and  FIG. 11 , a circuit  5  of the light string is shown according to a fifth embodiment of the present disclosure. 
     The circuit  5  includes a first wire  110 , a second wire  120 , a plurality of illumination devices  130 , and a third wire  160 . 
     Referring also to  FIG. 12 , each of the illumination devices  130  may be substantially identical to the illumination device  130  in the first embodiment or the other embodiment. Each of the illumination devices  130  includes a substrate  131  and a light source  132 . The substrate  131  includes a carrier portion  133 , an anode soldering portion (+) and a cathode soldering portion (−). The carrier portion  133  is located between the anode soldering portion (+) and the cathode soldering portion (−). The light source  132  is disposed on the carrier portion  133 , each of the illumination devices  130   a  are electrically connected to the first wire  110  by the anode soldering portions (+) and electrically connected to the second wire  120  by the cathode soldering portions (−). The detail of the illumination devices  130  is described in the first embodiment. 
     The difference of the illumination devices  130   a  in the fifth embodiment is that the illumination devices  130   a  may further include a controller  138 ; the controller  138  is combined with the substrate  131  for enabling and disabling the light source  132 . The controller  138  includes a signal input terminal DI and a signal output terminal DO; 
     Referring to  FIG. 10  and  FIG. 11 , the first wire  110  is used to receive a first electric potential V 1 ; and in one example, the first electric potential is 5V DC. The second wire provides a second electric potential V 2 , and in one example the second electric potential V 2  is GND. The third wire  160  includes a signal input end DATA IN and a signal output end DATA OUT, and a plurality of cut-off points C being arranged on the third wire  160 . Each of the illumination devices  130  is disposed at one of the cut-off points C respectively, and the signal input terminal DI and the signal output terminal DO are electrically connected to the third wire  160  respectively via different sides of the corresponding cut-off point C. The signal input terminal DI corresponds to the signal input end DATA IN of the third wire  160 . The signal output terminal DO corresponds to the signal output end DATA OUT of the third wire  160 . 
     The third wire  160  receives control signals for enabling and disabling the light source  132  via the signal input end DATA IN. The third wire  160  transfers the control signals to the controller  138  via the signal input terminal DI for controlling the corresponding light source  138 , and then the control signal is transferred to the controller  138  of the next illumination device  130   a  via the signal output terminal DO. Finally, the control signals are transferred to the circuit  5  of another light string. 
     As shown in  FIG. 11 , in an embodiment, the circuit  5  further includes a current-limiting resistor  180 , electrically connecting the first electric potential V 1  to the first wire  110  for limiting current in the first wire  110 . The current-limiting resistor  180  limits the current in the first wire  110 , so as to prevent the illumination devices  130  from being damaged by over-current. 
     In the present disclosure, the illumination devices  130  are securely soldered between the first wire  110  and the second wire  120 , and provide a good illumination effect. Moreover, the circuit of light string in the present disclosure provides a variety of approaches of power supply to adopt various type of light source, and ensures every light source can receive acceptable power input to prevent under voltage resulting from too many light sources.