Patent Publication Number: US-9845939-B2

Title: Light emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from and benefit of Korean Patent Application No. 10-2014-0142897 filed on Oct. 21, 2014, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     Apparatuses and methods consistent with exemplary embodiments relate to a light emitting device. 
     Demand for light emitting diodes (LED) is continuously increasing due to various advantages thereof, such as long lifespans, low power consumption, excellent initial driving performance, and high levels of vibration resistance as compared to light emitting devices based on filaments. On the other hand, since LEDs have characteristics of being driven by direct current (DC) power, light emitting devices using LEDs are commonly provided with rectifying circuits. However, such rectifying circuits may complicate the configurations of light emitting devices, or may cause mechanical issues therewith or decreases lifespans thereof. 
     SUMMARY 
     To address the above problems, there is a need for research into an alternating current (AC) direct driving scheme using, as driving power, DC power having the form of a sine wave rectified without a constant current circuit. 
     Exemplary embodiments of the inventive concept provide a light emitting device capable of readily changing output luminous flux, using an alternating current (AC) direct driving scheme. 
     According to an aspect of an exemplary embodiment, there is provided a light emitting device which may include: a plurality of light emitting modules each provided with a circuit board, and first to n-th light source groups disposed on the circuit board, n being an integer greater than two, wherein the first to n-th light source groups each include at least one light emitting diode (LED); a driving module supplying driving power to the plurality of light emitting modules, and determine a number of light source groups operating in each of the plurality of light emitting modules based on a level of the driving power; and a module connection unit connecting first to n-th light source groups provided in one of the plurality of light emitting modules to first to n-th light source groups provided in another light emitting module in parallel in a detachable manner, respectively. 
     The circuit boards provided in the plurality of light emitting modules, respectively, may be physically separated from one another. 
     The circuit board provided in each of the plurality of light emitting modules may include a wiring pattern, and the first to n-th light source groups provided in each of the plurality of light emitting modules are electrically connected to one another by the wiring pattern. 
     The module connection unit may include a connector disposed on the circuit board provided in each of the plurality of light emitting modules, and electrically connected to the wiring pattern provided on the circuit board. 
     The connector may include a plurality of connectors disposed on the circuit board provided in each of the plurality of light emitting modules. 
     The connector may be disposed adjacently to an edge of the circuit board provided in each of the plurality of light emitting modules. 
     The circuit board provided in each of the plurality of light emitting modules may have a surface on which light source groups provided in each of the plurality of light emitting modules are disposed, and the surface has a polygonal shape. 
     The surface may have a regular polygonal shape. 
     The circuit boards provided in the plurality of light emitting modules, respectively, may have substantially identical shapes to one another. 
     The circuit boards provided in the plurality of light emitting modules, respectively, may be arranged in a honeycomb structure. 
     The driving module may include a control unit controlling a path of currents applied to the plurality of light emitting modules and flowing to a ground, based on the level of the driving power. 
     The driving module may further include a rectifying unit rectifying externally applied AC power. 
     The driving module may be direct current (DC) power in a form of a sine wave. 
     The first to n-th light source groups provided in each of the plurality of light emitting modules may be connected to one another in series in a sequence of the first to n-th light source groups. 
     At least one of the plurality of light emitting modules may further include a resistor unit connected to the first to n-th light source groups in series. 
     The resistor unit may include a variable resistor. 
     Output luminous flux may be increased in proportion to a number of the light emitting modules electrically connected to one another by the module connection unit. 
     The driving module may be disposed on the circuit board provided in one of the plurality of light emitting modules. 
     According to an aspect of another exemplary embodiment, there is provided a light emitting device which may include a main module including a main board, a light source unit provided with first to n-th light source groups, n being an integer greater than two, and a driving unit supplying driving power to the light source unit; a sub-module including a sub-board physically separated from the main board, and first to n-th light source groups disposed on the sub-board and driven by the driving power supplied from the driving unit; and a module connection unit connecting the first to n-th light source groups provided in the light source unit of the main module to the first to n-th light source groups provided in the sub-module in parallel in a detachable manner, respectively, wherein the driving unit determines a number of light source groups operating in the first to n-th light source groups of the main module and a number of light source groups operating in the first to n-th light source groups of the sub-module, based on a level of the driving power. 
     According to still an aspect of still another exemplary embodiment, there is provided a light emitting device which may include a plurality of light emitting modules each including first to n-th light source groups, n being an integer greater than two, and physically separated from one another; a driving module supplying driving power to the plurality of light emitting modules, and determining a number of light source groups operating in each of the plurality of light emitting modules, based on a level of the driving power; and a module connection unit connecting the first to n-th light source groups provided in each of the plurality of light emitting modules to first to n-th light source groups provided in an adjacent light emitting module in parallel in a detachable manner, respectively. 
     According to still an aspect of still another exemplary embodiment, there is provided a light emitting device which may include at least one light emitting module including a plurality of light source groups, each including at least one light source, and a driving module configured to control turn-on and turn-off of the light source groups based on a level of power input to the driving module. Here, the driving module may be configured to turn on a different number of the light source groups as the level of the input power is changed. The at least one light emitting module may include a plurality of light emitting modules connected to one another, each including a plurality of light source groups, and, as the level of the input power is changed, the driving module may turn on the different number of the light source groups in each of the light emitting modules. Further, as the level of the input power is in a selected range, the driving module may turn on the same number of light source groups in the light emitting modules, respectively. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects, features and advantages of the exemplary embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram schematically illustrating a light emitting device, according to an exemplary embodiment; 
         FIGS. 2A and 2B  are perspective views schematically illustrating light emitting modules of a light emitting device, according to exemplary embodiments; 
         FIG. 3  is a perspective view schematically illustrating a light emitting device provided with the light emitting module, according to the exemplary embodiment of  FIGS. 2A and 2B ; 
         FIG. 4  is a circuit diagram illustrating an operation of the light emitting device illustrated in  FIG. 3 , according to an exemplary embodiment; 
         FIGS. 5A through 5C  are voltage waveform graphs illustrating operations of the light emitting device illustrated in  FIG. 3 , according to an exemplary embodiment; 
         FIGS. 6A through 6D  are circuit diagrams of a current path illustrating an operation of the light emitting device illustrated in  FIG. 3 , according to an exemplary embodiment; 
         FIGS. 7 and 8  are exploded perspective views schematically illustrating a light emitting device, according to exemplary embodiments; 
         FIG. 9  is a perspective view schematically illustrating a driving module of a light emitting device, according to an exemplary embodiment; 
         FIG. 10  is a perspective view schematically illustrating a light emitting device in a state in which a plurality of light emitting modules are mounted on the driving module according to the exemplary embodiment of  FIG. 9 ; 
         FIG. 11  is a circuit diagram illustrating an operation of the light emitting device illustrated in  FIG. 10 , according to an exemplary embodiment; and 
         FIGS. 12 and 13  are exploded perspective views schematically illustrating light emitting devices, according to exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments of the inventive concept will be described in detail with reference to the accompanying drawings. 
     The inventive concept may, however, be exemplified in many different forms and should not be construed as being limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. 
     In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements. 
     The terminology used herein is for the purpose of describing the exemplary embodiments set forth herein only and is not intended to be limiting of the inventive concept. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “include” “provided with” and/or “have” when used in the exemplary embodiments, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In the exemplary embodiments, terms such as “on,” “lateral surface,” “adjacent,” “in contact with,” and the like, are determined based on the drawings, and in actuality, the terms may be changed according to a direction in which a light emitting device is disposed in actuality. 
       FIG. 1  is a block diagram schematically illustrating a light emitting device according to an exemplary embodiment. 
     Referring to  FIG. 1 , a light emitting device according to an exemplary embodiment may include a plurality of light emitting modules  30 , a driving module  20 , and a module connection unit  40 . The plurality of light emitting modules  30  may be physically separated from one another, and may be electrically connected to one another by the module connection units  40 . As used herein, such physical separation may refer to physical separation without destroying or damaging a device. The plurality of light emitting modules  30  that are physically separated from one another may be connected to one another by the module connection units  40  in a detachable manner. The driving module  20  may be supplied with alternating current (AC) power from an external power source  10 , and may supply driving power to the plurality of light emitting modules  30 . 
     The driving module  20  and one or more of the plurality of light emitting modules  30  may be provided as a single main module  50 . The remainder of the plurality of light emitting modules  30  may be provided as a sub-module  60  or sub-modules  60  physically separated from the main module  50 . However, the number of light emitting modules to be provided along with the driving module in the single main module  50  and the number of the sub-modules  60  are not limited thereto. Thus, the driving module  20  and the plurality of light emitting modules  30  may be provided in a manner of being physically separated from one another as will be described in exemplary embodiments of  FIGS. 9 through 11 . 
       FIGS. 2A and 2B  are perspective views schematically illustrating the light emitting modules  30  of a light emitting device according to exemplary embodiments. 
     Referring to  FIG. 2A , the plurality of light emitting modules  30  may each include a circuit board  31  having a wiring pattern P, and a plurality of light source groups disposed on the circuit board  31  and electrically connected to one another by the wiring pattern P. 
     As illustrated in  FIG. 2A , the plurality of light emitting modules  30  may each include first to fourth light source groups G 1 , G 2 , G 3 , and G 4  electrically connected to one another by the wiring pattern P. However, the number of light source groups to be included in each of the plurality of light emitting modules is not limited thereto, and the plurality of light emitting modules may each include first to n-th light source groups, n being an integer greater than two. The first to n-th light source groups may each include at least one light emitting diode (LED) D. In the present exemplary embodiment, the light source groups G 1 , G 2 , G 3 , and G 4  are illustrated as each including two LEDs D. The first to n-th light source groups may be connected in series in a sequence of the first to n-th light source groups. 
     The circuit board  31  may be provided in order to dispose a plurality of light source groups. For example, the circuit board  31  may use a printed circuit board (PCB), a metal core printed circuit board (MCPCB), or a metal printed circuit board (MPCB). Also, a flexible printed circuit board (FPCB), which is easily transformable, may be used. However, the type of circuit board is not limited thereto, and a board formed of an organic resin material containing epoxy, triazine, silicon, polyimide, and the like, and other organic resin materials, a board formed of a ceramic material such as silicon nitride (SiN), aluminum nitride (AlN), or aluminum oxide (Al 2 O 3 ), or a board formed of a metal and a metal compound may also be used. 
     The circuit board  31  may have a surface on which the plurality of light source groups are disposed, and the surface may have a polygonal shape. For example, the circuit board  31  illustrated in  FIG. 2A  is illustrated as having a rectangular shape. The wiring pattern P may be formed on the surface; however, as necessary, the wiring pattern P may be formed on another surface of the circuit board  31  and/or in an interior of the circuit board  31 . 
     As described above, the plurality of light emitting modules  30  may be physically separated from one another, and it may be interpreted as the circuit boards provided in the plurality of light emitting modules  30 , respectively, being physically separated from one another. 
     The physically separated light emitting modules  30  may be electrically connected to one another by the module connection units  40 . To this end, the module connection unit  40  may include a connector  41  disposed on the circuit board  31  provided in each of the plurality of light emitting modules  30 . The connector  41  may be electrically connected to the wiring pattern P. 
     In the present exemplary embodiment, the module connection unit  40  may connect the first to n-th light source groups provided in each of the plurality of light emitting modules  30  to first to n-th light source groups provided in an adjacent light emitting module in parallel, respectively. In detail, the module connection unit  40  may connect first to n-th light source groups provided in one of the plurality of light emitting modules  30  and first to n-th light source groups provided in another light emitting module  30  to one another in parallel, respectively. In other words, in a case in which the plurality of light emitting modules  30  each include the first to fourth light source groups G 1 , G 2 , G 3 , and G 4 , the module connection unit  40  may connect the first light source groups G 1  of the respective light emitting modules  30  to one another in parallel. In a similar manner, the second to fourth light source groups G 2 , G 3 , and G 4  provided in each of the plurality of light emitting modules  30  may be connected to second to fourth light source groups G 2 , G 3 , and G 4  provided in an adjacent light emitting module in parallel, respectively. To enable such a parallel connection of the light source groups, the connector  41  may be electrically connected to one nodes a, b, c, and d of respective light source groups and the other node e of the last light source group by the wiring pattern P. 
     The connector  41  may include a plurality of connectors to be disposed on a single circuit board  31 . Accordingly, a single light emitting module  30  may be connected to a plurality of other light emitting modules  30 . For example, as illustrated in  FIG. 2A , a single light emitting module  30  may be connected to two separate light emitting modules  30  by two connectors  41  disposed on both edges of the circuit board  31 , respectively. Although not limited hereto, the connector  41  may be disposed adjacently to one of the edges of the circuit board  31  to facilitate connections among the light emitting modules  30 . 
     As illustrated in  FIG. 2B , the driving module  20  may be disposed on a circuit board  31   a  of at least one of the light emitting modules  30 . That is, one of the light emitting modules  30  may serve as the main module  50  provided with both the light emitting module  30  and the driving module  20 , and the remainder of the light emitting modules  30  not provided with the driving module  20  may serve as the sub-modules  60  in a single light emitting device. 
     In the present embodiment, the circuit board  31   a  and the circuit board  31  provided in the main module  50  and the sub-module  60 , respectively, will be referred to as a main board and a sub-board, respectively. In this case, the main board and the sub-board may be physically separated from one another, and the wiring patterns P may be formed on the main board and the sub-board, respectively. Also, a driving unit corresponding to the driving module  20 , and a light source unit corresponding to the first to n-th light source groups may be disposed on the main board. Also, a light source unit corresponding to the first to n-th light source groups may be disposed on the sub-board. At least one connector  41  may be disposed on each of the main board and the sub-board. 
     The driving module  20  may supply driving power to the plurality of light emitting modules  30 . Also, the driving module  20  may determine the number of light source groups operating in each of the plurality of light emitting modules  30  based on a level of the driving power. For example, in a case in which the plurality of light emitting modules  30  each includes four light source groups G 1 , G 2 , G 3 , and G 4 , the driving module  20  may allow only the first light source group G 1  to operate in each of the plurality of light emitting modules  30  in a case in which the level of the driving power is relatively low. As the level of the driving power is increased, the driving module  20  may control the number of light source groups operating in each of the plurality of light emitting modules  30 , such that the first and second light source groups G 1  and G 2 , the first to third light source groups G 1 , G 2 , and G 3 , or the first to fourth light source groups G 1 , G 2 , G 3 , and G 4  may operate in each of the plurality of light emitting modules  30 . 
       FIG. 3  is a perspective view schematically illustrating a light emitting device provided with the light emitting module according to the exemplary embodiment of  FIGS. 2A and 2B .  FIGS. 4 and 5A-5C  are a circuit diagram and a voltage waveform graph, respectively, illustrating an operation of the light emitting device illustrated in  FIG. 3 .  FIGS. 6A through 6D  are circuit diagrams of a current path illustrating an operation of the light emitting device illustrated in  FIG. 3 . 
     Referring to  FIG. 3 , in the light emitting device according to the present exemplary embodiment, the light emitting module  30  having the driving module  20  disposed on the circuit board  31   a  thereof, for example, the main module  50  with reference to  FIG. 2B , and the two light emitting modules  30  not having the driving module  20  disposed on the circuit board  31  thereof, for example, the two sub-modules  60  with reference to  FIG. 2A , may be electrically connected to one another by the module connection unit  40 . 
     Hereinafter, the operation of the light emitting device illustrated in  FIG. 3  will be described in greater detail with reference to  FIGS. 4, 5A-5C and 6A-6D . 
     Referring to  FIG. 4 , the driving module  20  may be supplied with an AC power from the external power source  10 . In this case, the driving module  20  may include a rectifier configured to rectify the AC power. Although the rectifier  21  is illustrated as a bridge diode full-wave rectifying AC power, the type of rectifier  21  is not limited thereto. Power rectified in the rectifier  21  may be supplied to the plurality of light emitting modules  30  to serve as driving power for driving a light source group. Here, the driving power may be DC power in a form of a sine wave as illustrated in  FIGS. 5A-5C . 
     The driving module  20  may determine the number of light source groups operating in each of the plurality of light emitting modules  30  based on a level of the driving power. To this end, the driving module  20  may include a controller  22  configured to control a path of currents applied to the plurality of light emitting modules  30  and flow into a ground based on the level of the driving power. In detail, the controller  22  may change a path of currents passing through at least one of the first to n-th light source groups provided in the plurality of light emitting modules  30  and flowing into the ground, based on the level of the driving power varying in predetermined periods of time. 
     Although not limited hereto, the controller  22  may include a plurality of switches Q 1 , Q 2 , and Q 3  forming connections between the ground and each of the nodes b, c, and d of respective light source groups, and a switching controller  22   a  controlling switching operations of the plurality of switches Q 1 , Q 2 , and Q 3 . Although not limited hereto, the plurality of switches Q 1 , Q 2 , and Q 3  may use, for example, a transistor device, and the switching controller  22   a  may include a comparator. The comparator may include an operational amplifier (OP Amp). 
     The controller  22  may further include a detector  22   b  detecting the level of the driving power. The detector  22   b  may include, for example, a resistor device, and may be inserted into an appropriate position in the controller  22  to detect a level of currents applied to the plurality of light emitting modules  30 . 
     Hereinafter, the operation of the light emitting device based on the level of the driving power will be described in greater detail with reference to  FIGS. 5A-5C and 6A-6D . 
     The voltage waveform graphs in  FIGS. 5A-5C  illustrate voltages Va, Vb, and Vc in one nodes a of the first light source groups of the three light emitting modules  30  illustrated in  FIG. 4 , respectively. Referring to  FIGS. 5A-5C , a voltage level of the driving power may vary in predetermined periods of time, and based on threshold voltage characteristics of the LED D (see  FIGS. 2A-2B ), in a case in which the voltage level of the driving power is higher than a level of a minimum voltage Vth 1  capable of driving the first light source group G 1  and is lower than a level of a minimum voltage Vth 2  capable of driving the first and second light source groups G 1  and G 2 , that is, in a case in which the driving power is in a first driving interval t 1 , the control unit  22  may turn on the first switch Q 1  connected to the node b between the first light source group G 1  and the second light source group G 2  as illustrated in  FIG. 6A , and may control currents applied to each of the plurality of light emitting modules  30  to pass through the first light source group G 1  and flow into the ground. In this case, only the first light source group G 1  may operate in each of the light emitting modules  30 . 
     In a case in which the level of the driving power is higher than the level of the minimum voltage Vth 2  capable of driving the first and second light source groups G 1  and G 2  and is lower than a level of a minimum voltage Vth 3  capable of driving the first to third light source groups G 1  to G 3 , that is, in a case in which the driving power is in a second driving interval t 2 , the control unit  22  may turn off the first switch Q 1 , may turn on the second switch Q 2  connected to the node c between the second light source group G 2  and the third light source group G 3  as illustrated in  FIG. 6B , and may control the currents applied to each of the plurality of light emitting modules  30  to pass through the first and second light source groups G 1  and G 2  and flow into the ground. In this case, only the first and second light source groups G 1  and G 2  may operate in each of the light emitting modules  30 . 
     In a case in which the level of the driving power is higher than the level of the minimum voltage Vth 3  capable of drive driving the first to third light source groups G 1 , G 2 , and G 3  and is lower than a level of a minimum voltage Vth 4  capable of drive driving the first to fourth light source groups G 1 , G 2 , G 3 , and G 4 , that is, in a case in which the driving power is in a third driving interval t 3 , the control unit  22  may turn off the first and second switches Q 1  and Q 2 , may turn on the third switch Q 3  connected to the node d between the third light source group G 3  and the fourth light source group G 4  as illustrated in  FIG. 6C , and may control the currents applied to each of the plurality of light emitting modules  30  to pass through the first to third light source groups G 1 , G 2 , and G 3  and flow into the ground. In this case, only the first to third light source groups G 1 , G 2 , and G 3  may operate in each of the light emitting modules  30 . 
     In a case in which the level of the driving power is higher than a level of a minimum voltage Vth 4  capable of drive driving the first to fourth light source groups G 1 , G 2 , G 3 , and G 4 , that is, in a case in which the driving power is in a fourth driving interval t 4 , the control unit  22  may control the currents applied to each of the plurality of light emitting modules  30  to pass through all of the first to fourth light source groups G 1 , G 2 , G 3 , and G 4  and flow into the ground. In this case, as illustrated in  FIG. 6D , all of the first to third switches Q 1 , Q 2 , and Q 3  may be turned off, and the first to fourth light source groups G 1 , G 2 , G 3 , and G 4  may operate in each of the light emitting modules  30 . 
     In  FIG. 4 , the nodes a-e of one light emitting module are connected to the nodes a-e of the other light emitting modules, respectively. However, the inventive concept is not being limited to this configuration a light emitting device. According to another exemplary embodiment, the node a of one light emitting module may be connected to the node b of another light emitting module which is connected to the node c of another light emitting module through the module connection unit. 
     Since the light emitting device according to the present exemplary embodiment is provided with a plurality of light emitting modules rather than a single light emitting module, a plurality of light emitting modules, for example, three light emitting modules may operate in each driving interval of the driving power, for example, first to fourth driving intervals. In this case, luminous flux output from the light emitting device may be increased in proportion to the number of light emitting modules  30  being provided. Although not limited hereto, the luminous flux of the light emitting device may be increased in direct proportion to the number of light emitting modules  30 . 
     According to the present exemplary embodiment, since the light emitting modules  30  are connected to one another by the module connection unit  40  in a detachable manner, an additional light emitting module  30  may be included in a light emitting device as necessary. In this case, a light emitting device in an AC direct driving scheme capable of readily changing output luminous flux may be achieved. 
     In the exemplary embodiment, the light emitting module  30  may further include a resistor unit  32  connected to the first to n-th light source groups in series, as necessary as illustrated in  FIG. 4 . The resistor unit  32  may adjust an amount of currents flowing in each of the plurality of light emitting modules  30  by changing impedance of the light emitting device. In other words, luminous flux of light emitted from each of the plurality of light emitting modules  30  may be adjusted. The resistor unit  32  may be a resistor device having a fixed resistance level; however, the type of resistor unit is not limited thereto, and may include a variable resistor. 
       FIG. 7  is an exploded perspective view schematically illustrating a light emitting device according to an exemplary embodiment. 
     Referring to  FIG. 7 , in the present exemplary embodiment, the light emitting device may include a driving module  20 , a plurality of light emitting modules  30 , and a module connection unit  40 . Hereinafter, descriptions of elements the same as those provided above will be omitted, and different configurations will mainly be described. 
     The plurality of light emitting modules  30  may include a circuit board  31  and a plurality of light source groups disposed on the circuit board  31 . In the present exemplary embodiment, the plurality of light emitting modules  30  may each include first to fourth light source groups G 1 , G 2 , G 3 , and G 4 , and each light source group may be illustrated as including four LEDs D connected to one another in series by a wiring pattern P. The driving module  20  may be disposed on the circuit board of one of the plurality of light emitting modules  30 . 
     The plurality of light emitting modules  30  may be connected to one another by the module connection unit  40 . The module connection unit  40  may include a connector  41  disposed on the circuit board  31  provided in each of the plurality of light emitting modules  30 . Although not limited hereto, the connector  41  may include a plurality of connectors to be disposed on the circuit board  31 . 
     In the present exemplary embodiment, the circuit board  31  provided in each of the plurality of light emitting modules  30  may have a surface on which the light source groups are disposed, and the surface of each of the plurality of light emitting modules  30  may have a polygonal shape. Although not limited hereto, the surface of each of the plurality of light emitting modules  30  may have a regular polygonal shape. For example, as illustrated in  FIG. 7 , the surface of each of the plurality of light emitting modules  30  may have an equilateral triangular shape. The circuit boards  31  provided in the plurality of light emitting modules  30 , respectively, may have substantially different shapes and sizes from one another. Each circuit board  31  may be disposed in a manner that lateral surfaces thereof are in contact with those of other adjacent circuit boards  31 , and thereby mounting density of the plurality of light emitting modules  30  may be increased, and relatively uniform light emitting distribution may be achieved. 
     In the present exemplary embodiment, the light emitting device may include a housing  110  in which the plurality of light emitting modules  30  are mounted, and a cover unit  120  through which light emitted from the plurality of light emitting modules  30  is dissipated externally. 
     The housing  110  may have a box-type structure including a surface  111  on which the plurality of light emitting modules  30  are disposed, and a lateral surface  112  extending from a circumference of the surface  111 . The housing  110  may be formed of a material, for example, a metal, having relatively high thermal conductivity in order to externally dissipate heat generated in the plurality of light emitting modules  30 , the driving module  20 , and the like. For relatively enhanced heat radiating efficiency, a heat sink  130  may be attached to the housing  110 . The heat sink  130  may be provided with a plurality of heat dissipation fins  131 . 
     The cover unit  120  may be mounted on the housing  110 , and may be formed of a light transmissive material. The cover unit  120  may contain a light diffusive material to allow light emitted from the plurality of light emitting modules  30  to be dissipated externally in a uniform manner. Also, the cover unit  120  may have a convex lens shape, a concave lens shape, or the like, for optical effects. 
       FIG. 8  is an exploded perspective view schematically illustrating a light emitting device according to an exemplary embodiment. Hereinafter, descriptions of elements the same as those provided in  FIG. 7  will be omitted, and different configurations will mainly be described. In  FIG. 8 , an illustration of a wiring pattern provided in each circuit board  31  is omitted. 
     In the present exemplary embodiment, the circuit board  31  provided in each of a plurality of light emitting modules  30  may have a surface on which light source groups are disposed, and the surface of each of the plurality of light emitting modules  30  may have a regular hexagonal shape. Each circuit board  31  may be disposed in a manner that lateral surfaces thereof are in contact with those of other adjacent circuit boards  31 . Accordingly, the circuit boards  31  may be arranged in a honeycomb structure. In this case, mounting density of the plurality of light emitting modules  30  may be increased, and relatively uniform light emitting distribution may be achieved. 
     A plurality of connectors  41  may be disposed on each circuit board  31 . The connectors  41  may be disposed on edges of the surface of the circuit board  31 , respectively. However, the number of connectors  41  to be disposed on the circuit board  31  is not limited thereto, and may be adjusted in various manners as necessary. 
       FIGS. 9 through 11  are views illustrating a light emitting device according to exemplary embodiments. 
       FIG. 9  is a perspective view schematically illustrating a driving module  20  of a light emitting device according to an exemplary embodiment.  FIG. 10  is a perspective view schematically illustrating a light emitting device in a state in which a plurality of light emitting modules  30  are mounted on the driving module  20  according to the exemplary embodiment of  FIG. 9 .  FIG. 11  is a circuit diagram illustrating an operation of the light emitting device illustrated in  FIG. 10 . 
     Referring to  FIGS. 9 and 10 , the driving module  20  according to the present exemplary embodiment may be disposed on a circuit board including a wiring pattern P. The circuit board may not include a light source group disposed thereon. Hereinafter, the circuit board including the driving module  20  disposed thereon while not including the light source group disposed thereon will be referred to as a driving module board  23 . 
     The driving module board  23  may be physically separated from the circuit board  31  provided in each of the plurality of light emitting modules  30 . The driving module  20  and the light emitting module  30  may be electrically connected to one another by module connection units  40  in a detachable manner. 
     The module connection units  40  may include connectors  41 , respectively, disposed on the driving module board  23  and the circuit board  31  provided in the light emitting module  30  for an electrical connection between the driving module  20  and the light emitting module  30 . 
     The plurality of light emitting modules  30  illustrated in  FIG. 10  may include the circuit board  31  and a plurality of light source groups disposed on the circuit board  31 .  FIG. 10  illustrates that the plurality of light source groups may include first to fourth light source groups G 1 , G 2 , G 3 , and G 4 , and each light source group may include a single LED D; however, the number of light source groups to be included in the light emitting module and the number of LEDs to be included in the light source group are not limited thereto. In  FIG. 10 , illustration of a wiring pattern is omitted. 
     Referring to  FIG. 11 , the driving module  20  may determine the number of light source groups operating in each of the plurality of light emitting modules  30  based on a level of driving power. For example, in a case in which the level of the driving power is relatively low, the driving module  20  may enable only the first light source group G 1  to operate, and in a case in which the level of the driving power is relatively high, the driving module  20  may set the number of operating light source groups to be increased. 
     Luminous flux output from the light emitting device may be changed based on the number of the light emitting modules  30 . In the present exemplary embodiment, since the light emitting module  30  may be connected to the driving module  20  and to the other light emitting modules  30  by the module connection units  40  in a detachable manner, the number of the light emitting modules  30  to be included in the light emitting device may be readily changed. Accordingly, maximum luminous flux output from the light emitting device may also be readily changed. 
       FIG. 12  is an exploded perspective view schematically illustrating a light emitting device according to an exemplary embodiment. As illustrated in  FIG. 12 , the light emitting device may be applied to a bulb-type lamp. 
     In the present exemplary embodiment, the light emitting device may include a housing  210 , and a plurality of light emitting modules  30 , a driving module  20 , and a module connection unit  40  to be installed in the housing  210 . The driving module  20  may be disposed on a circuit board provided in one of the plurality of light emitting modules  30 . However, the type of board on which the driving module  20  is to be disposed is not limited thereto, and the driving module  20  may be disposed on a separate driving module board and may be electrically connected to the plurality of light emitting modules  30  by the module connection units  40 . The plurality of light emitting modules  30  may be combined with one another by the module connection units  40  in a detachable manner. 
     The housing  210  may serve as a frame supporting the plurality of light emitting modules  30 , and as a heat sink externally dissipating heat generated in the light emitting modules  30 . To this end, the housing  210  may be formed of a rigid material having relatively high thermal conductivity. For example, the housing  210  may be formed of a metal material such as aluminum (Al), or a heat radiating resin. An outer lateral surface of the housing  210  may include a plurality of heat dissipation fins  211  for significantly enhancing heat radiating efficiency by increasing a contact area thereof with air. The light emitting device may include a terminal unit  230  transferring externally supplied power to the driving module  20 . 
     A cover unit  220  disposed on the housing  210  may encapsulate the light emitting module, and may have a convex lens shape or a bulb shape. The cover unit  220  may be formed of a light transmissive material, and may contain a light diffusive material. 
       FIG. 13  is an exploded perspective view schematically illustrating a light emitting device according to an exemplary embodiment. As illustrated in  FIG. 13 , the light emitting device may be applied to a bar-type lamp. 
     In the present exemplary embodiment, the light emitting device may include a housing  310 , and a plurality of light emitting modules  30 , a driving module  20 , and a module connection unit  40  to be installed in the housing  310 . The driving module  20  may be disposed on a separate driving module board  23  physically separated from the circuit board  31  provided in each of the plurality of light emitting modules  30 . The module connection unit  40  may electrically connect the driving module  20  and the plurality of light emitting modules  30  to one another. The module connection unit  40  may include the connector  41  disposed on both of the driving module board  23  and the circuit board  31  provided in each of the plurality of light emitting modules  30 . The plurality of light emitting modules  30  and the driving module  20  may be combined with one another by the module connection units  40  in a detachable manner. 
     The housing  310  may have a shape extending in a direction thereof, and may be formed of a material having relatively high thermal conductivity. A plurality of heat dissipation fins  312  used for dissipating heat may be provided on both lateral surfaces of the housing  310  while protruding therefrom. 
     The housing  310  may include a cover unit  320  disposed thereon. The cover unit  320  may be fastened to a fastening groove  311  of the housing  310  so as to encapsulate the light emitting module  30 . A protrusion portion  321  engaged with the fastening groove  311  of the housing  310  may be formed on a bottom surface of the cover unit  320  in a lengthwise direction of the housing  310 . The cover unit  320  may have a semicircular curved surface to allow light generated in the light emitting module  30  to be dissipated externally in a uniform manner. 
     A terminal unit  330  may be provided in an open end portion of the housing  310  in the lengthwise direction thereof, and may supply external power to the driving module  20 . The terminal unit  330  may include an outwardly protruding electrode pin  331 . 
     According to the present exemplary embodiment, luminous flux output from the light emitting device may be readily changed by simply changing the number of light emitting modules to be provided in the light emitting device. 
     As set forth above, according to exemplary embodiments in the present disclosure, the light emitting device capable of driving without using a constant current circuit may be achieved. Also, in such a light emitting device using an AC direct driving scheme, luminous flux output from the light emitting device may be readily changed. 
     Various advantages and effects of the exemplary embodiments are not limited to the above-described descriptions and may be easily understood through explanations of concrete embodiments in the present disclosure. 
     While exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the inventive concept as defined by the appended claims.