Patent Publication Number: US-2010109566-A1

Title: Control Circuit for Light Emitting Diode and Light Emitting Device Having the Same

Description:
TECHNICAL FIELD 
     The embodiment relates to a control circuit for a light emitting diode and a light emitting device having the same. 
     BACKGROUND ART 
     Light Emitting Diodes (LEDs) produce light having various colors by using compound semiconductor materials based on GaAs, AlGaAs, GaN, InGaN, InGaAlP, etc. Such LEDs have been applied to various fields such as a lightening indicator, a character indicator and an image indicator (for example, an LCD), in which at least one LED is used to display a unique color or various colors. 
     Disclosure of Invention 
     Technical Problem 
     The embodiment provides a control circuit for a light emitting diode and a light emitting device having the same, capable of sequentially controlling light emitting diodes according to colors thereof. 
     The embodiment provides a control circuit for a light emitting diode and a light emitting device having the same, capable of sequentially controlling ON/OFF modes of a red LED, a green LED and a blue LED according to a state of a 2-bit control signal. 
     Technical Solution 
     An embodiment provides a control circuit for a light emitting diode comprising; a red LED, a green LED and a blue LED; a driver which outputs a first control signal and a second control signal based on a 2-bit combination; and a driving circuit which sequentially turns on/off the LEDs according to a state of the first control signal and the second control signal that are output from the driver. 
     An embodiment provides a light emitting device comprising; a package body having a cavity; first to third color LEDs disposed in the cavity; a driving circuit, which is connected to first electrodes of the first to third color LEDs in a predetermined area of the package body to turn on/off the first to third color LEDs; a plurality of control signal terminals, which are disposed at a first side of the package body and are connected to the driving circuit; and a ground terminal, which is disposed at a second side of the package body and is connected to a second electrode of the first to third colors. 
     An embodiment provides a light emitting device comprising; a substrate, on which a light emitting diode comprising first to third LED chips is disposed in a form of an array; a driving circuit connected to a first electrode and a second electrode of the LED chips through four signal lines to sequentially operate the LED chips; and a driver, which outputs a first control signal and a second control signal having a 2-bit combination to the driving circuit. 
     Advantageous Effects 
     According to the embodiment, a lightening operation of a red LED, a green LED and a blue LED can be controlled according to a 2-bit control signal. 
     According to the embodiment, ON/OFF operations of a red LED, a green LED and a blue LED can be sequentially controlled according to a 2-bit control signal. 
     According to the embodiment, two electrodes of three color LEDs are connected through four signal lines, so that a line pattern of a substrate is simplified and a sufficient space is ensured for the substrate. 
     The embodiment provides a control circuit for a light emitting diode, which is applied to an FSC (Field Sequential Color) type display device and a light unit having the same. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram representing a control circuit for a light emitting diode according to an embodiment; 
         FIG. 2  is a plan view representing a light emitting device having a driving circuit shown in  FIG. 1 ; 
         FIG. 3  is a sectional view taken along line A-A of  FIG. 2 ; 
         FIG. 4  is a view representing a display device adopting a side-view type light unit having the driving circuit shown in  FIG. 1 ; 
         FIG. 5  is a view representing a display device adopting a top-view type light unit having the driving circuit shown in  FIGS. 1 ; and 
         FIG. 6  is a plan view representing an example of a light emitting unit shown in  FIG. 5 . 
     
    
    
     BEST MODE FOR CARRYING OUT OF THE INVENTION 
     Hereinafter, the embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a view representing a control circuit for a light emitting diode according to an embodiment. 
     As shown in  FIG. 1 , a control circuit  101  comprises a light emitting diode unit  130 , a driver  140  and a driving circuit  150 . 
     The light emitting diode unit  130  comprises a red light emitting diode  131 , a green light emitting diode  132  and a blue light emitting diode  133 . At least one of the red, green and blue light emitting diodes  131 ,  132  and  133  comprises at least one LED. The red, green and blue light emitting diodes  131 ,  132  and  133  are turned on by the driving circuit  150  at different time points. 
     The light emitting diode unit  130  does not limit three color LEDs(a red LED, a green 
     LED and a blue LED). The LEDs may be changed to other color LED (for example, an yellow LED) and can be added other color LED. 
     The driver  140  outputs power to the driving circuit  150  by converting the power into 2-bit control signals S 1  and S 2 . The driving circuit  150  sequentially controls an operation of the light emitting diodes  131 ,  132  and  133  according to the control signals S 1  and S 2 . 
     The driver  140  outputs the two control signals S 1  and S 2  in the form of a 2-bit logic signal. The 2-bit logic signal comprises states of 00, 10, 01 and 11. The state of signal  1  represents a high level, and the state of signal  0  represents a low level. 
     The driver  140  performs a time division with respect to a first control signal S 1  and a second control signal S 2  in the order of 00, 10, 01 and 11 to output the control signals S 1  and S 2  to the driving circuit  150 . Such a driver  140  outputs the control signals S 1  and S 2  having a 2-bit combination during a period or a frame. 
     The driving circuit  150  is connected between the driver  140  and the light emitting diodes  131 ,  132  and  133 , and sequentially drives the light emitting diodes  131 ,  132  and  133  according to the state of the first and second control signals S 1  and S 2  that are output from the driver  140 . 
     The driving circuit  150  comprises inversion logic devices  151  and  152 , and AND logic devices  153 ,  154  and  155 . 
     The inversion logic devices  151  and  152  serve as an inverter that outputs an input signal into an inverted signal, and comprises a first inversion logic device  151  for inverting the first control signal S 1  and a second inversion logic device  152  for inverting the second control signal S 2 . 
     The AND logic devices  153 ,  154  and  155  are prepared in the form of an AND gate, which ANDs two input signals to output a single signal, and comprise a first AND logic device  153 , a second AND logic device  154  and a third AND logic device  155 . 
     The first to third AND logic devices  153 ,  154  and  155  are connected to the red light emitting diode  131 , the green light emitting diode  132  and the blue light emitting diode  133 , respectively. The inversion logic devices  151  and  152 , and the AND logic devices  153 ,  154  and  155  are realized as a combination circuit of a transistor. 
     A buffer may be disposed between the inversion logic devices  151  and  152  and the driver  140 . In addition, the buffer may be provided at an input terminal of the inversion logic devices  151  and  152 , or an input terminal of the AND logic devices  153 ,  154  and  155 . 
     The first inversion logic device  151  inverts the first control signal S 1  to output the inverted first control signal to the second AND logic device  154 . The second inversion logic device  152  inverts the second control signal S 2  to output the inverted second control signal to the first AND logic device  153 . 
     The first AND logic device  153  ANDs the input first control signal S 1  and the inverted signal of the second inversion logic device  152  to output a resultant signal to a first electrode  121  of the red light emitting diode  131 . 
     The second AND logic device  154  ANDs the inverted signal of the first inversion logic device  151  and the input second control signal S 2  to output a resultant signal to a first electrode  122  of the green light emitting diode  132 . 
     The third AND logic device  155  ANDs the input first and second control signals S 1  and S 2  to output a resultant signal to a first electrode  123  of the blue light emitting diode  133 . 
     The red, green and blue light emitting diodes  131 ,  132  and  133  are driven by signals applied to the first electrodes  121 ,  122  and  123 . A second electrode  124  of the red, green and blue light emitting diodes  131 ,  132  and  133  are connected to a ground terminal GND. 
     Such a driving circuit  150  turns on/off the red, green and blue light emitting diodes  131 ,  132  and  133  by using two control signal terminals and the single ground terminal GND. An arrangement of devices of the driving circuit  150  and a sequence of ON/OFF operations may be changed according to the embodiments. 
     Table 1 represents an example of an operation mode of the light emitting diode according to the control signals of the driver and the driving circuit. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 FIRST CONTROL 
                 SECOND CONTROL 
                   
               
               
                 SIGNAL 
                 SIGNAL 
                 LED ON/OFF 
               
               
                   
               
             
            
               
                 0 
                 0 
                 LED OFF 
               
               
                 1 
                 0 
                 RED LED ON 
               
               
                 0 
                 1 
                 GREEN LED ON 
               
               
                 1 
                 1 
                 BLUE LED ON 
               
               
                   
               
            
           
         
       
     
     As shown in TABLE 1, when the first control signal S 1  and the second control signal S 2  of the driver  140  are input to the driving circuit  150  in the 00 state, the first inversion logic device  151  and the second inversion logic device  152  output a HIGH signal, respectively. In this case, the first to third AND logic devices  153 ,  154  and  155  output a LOW signal based on the first signal S 1  or second signal S 2 . Accordingly, the light emitting diodes  131 ,  132  and  133  become an OFF state. 
     When the first control signal S 1  and the second control signal S 2  of the driver  140  are input to the driving circuit  150  in the 10 state, the first AND logic device  153  ANDs the first control signal S 1  and the inverted signal of the second inversion logic device  152  to output a high signal to the red light emitting diode  131 . Accordingly, the red light emitting diode  131  becomes an ON state and the remaining light emitting diodes  132  and  133  become an OFF state. 
     When the first control signal S 1  and the second control signal S 2  are input to the driving circuit  150  in the 01 state, the second AND logic device  154  ANDs the inverted signal of the first inversion logic device  151  and the second control signal S 2  to output a high signal to the green light emitting diode  132 . Accordingly, the green light emitting diode  132  becomes an ON state, and the remaining light emitting diodes  131  and  133  become an OFF state. 
     When the first control signal S 1  and the second control signal S 2  of the driver  140  are input to the driving circuit  150  in the  11  state, the third AND logic device  155  ANDs the first control signal S 1  and the second control signal S 2  to output a high signal to the blue light emitting diode  133 . Accordingly, the blue light emitting diode  133  becomes an ON state, and the remaining light emitting diodes  131  and  132  become an OFF state. 
     The driving circuit  150  enables an LED-OFF mode, a red LED-ON mode, a green LED-ON mode and a blue LED-ON mode according to a logical state of the 2-bit control signals S 1  and S 2 . 
     In addition, the driving circuit  150  sequentially controls the ON/OFF sequence of three color LEDs (a red LED, a green LED and a blue LED) or a plurality of light emitting diodes according to a time division state of the 2-bit control signals S 1  and S 2 , so that the multi-color LEDs or a plurality of LEDs are sequentially operated. The ON/OFF sequence of the three color LEDs may be changed according to the embodiments. 
     Such a driving circuit  150  is realized in an LED package or is realized as a circuit on a printed circuit board. 
       FIG. 2  is a view representing a light emitting device comprising the driving circuit shown in  FIG. 1 , and  FIG. 3  is a sectional view taken along line A-A of  FIG. 2 . 
     As shown in  FIGS. 2 and 3 , a light emitting device  102  comprises a package body  110  having a cavity  114 , light emitting diodes  131 ,  132  and  133  and a driving circuit  150 . 
     The package body  110  comprises a printed circuit board (PCB). The package body  110  is made from silicon, ceramic, such as silicon carbide (SiC) and aluminum nitride (AlN), thermosetting resin, such as poly phthal amide (PPA) and liquid crystal polymer, and a mixture thereof. 
     The package body  110  comprises a lower substrate  111  and an upper substrate  112 , which are vertically stacked, and a predetermined electrode pattern is formed on the lower substrate  111 . 
     The cavity  114  is formed at the center of the upper substrate  112 . The cavity  114  has a depth sufficient for exposing the electrode pattern of the lower substrate  111  to the outside. Such a package body  110  can be obtained by stacking substrates or can be integrally formed through an injection molding process. 
     Electrodes  121 ,  122 ,  123  and  124  are formed on the lower substrate  111 , and the light emitting diodes  131 ,  132  and  133  are electrically connected to the electrodes  121 ,  122 ,  123  and  124 . In addition, an inner wall  116  of the upper substrate  112  may be inclined, and may be coated with a light reflection material. 
     The light emitting diodes  131 ,  132  and  133  are provided in the form of chip, and are connected to first electrodes  121 ,  122  and  123  and a second electrode  124  through a wire  135 . The first electrodes  121 ,  122  and  123  are connected to the driving circuit  150 , and the second electrode  124  is connected to a ground terminal GND. The light emitting diodes  131 ,  132  and  133  can be connected to the first and second electrodes  121 ,  122 ,  123  and  124  through a wire bonding scheme, a die bonding scheme and a flip boding scheme according to the type of a semiconductor chip. 
     A first control signal terminal  141 , a second control signal terminal  142  and a ground terminal  143  are disposed at an outer side of the package body  110 . 
     The driving circuit  150  is provided on the lower substrate  111  of the package body  110  in the form of a combination of MOS transistor. Such a driving circuit  150  sequentially controls a lightening sequence of the three color LEDs  131 ,  132  and  133  by using the three signal terminals  141 ,  142  and  143 . 
     The driving circuit  150  sequentially turns on/off the red light emitting diode  131 , the blue light emitting diode  132  and the green light emitting diode  132  as shown in TABLE 1 according to the state of 2-bit control signals which are input to the first and second control signal terminals  141  and  142 . 
     Resin material such as transparent epoxy or silicon is molded in the cavity  114 . The resin material may have a flat shape, a concave lens shape or a convex lens shape according to a surface state of the resin material. 
     The light emitting device  102  sequentially controls an LED OFF mode and ON/OFF modes of color LEDs according to a sequence of the 2-bit logical signals, which are input into the first and second control signal terminals  141  and  142 . 
       FIG. 4  is a perspective view representing a side-view type display device having the driving circuit of  FIG. 1 . 
     As shown in  FIG. 4 , a display device  200  comprises a reflection plate  201 , a light guide plate  203 , an optical sheet  205 , a display panel  207  and a light emitting unit  210 . The reflection plate  201 , the light guide plate  203 , the optical sheet  205  and the light emitting unit  210  may serve as a light unit. 
     The reflection plate  201  reflects light, which is leaked toward the lower side of the light guide plate  203 . Such a reflection plate  201  may comprise a plate having high reflectivity or can be coated on a chassis. 
     The light emitting plate  203  guides incident light into a light emitting area and allows the incident light to have an optical distribution of a surface light source. A predetermined pattern may be formed at one side or both sides of the light guide plate  203 . 
     The optical sheet  205  comprises at least one of a diffusion sheet, a horizontal prism sheet, a vertical prism sheet and a brightness enhancement sheet. The diffusion sheet diffuses incident light, and the horizontal prism sheet and the vertical prism sheet concentrate light in a horizontal direction and a vertical direction, respectively. The brightness enhancement sheet enhances brightness. Such an optical sheet  205  allows light to be irradiated to the display panel  207  with a uniform brightness distribution. 
     A polarizer (not shown) may be attached to an upper side and/or a lower side of the display panel  207 . 
     The display panel is realized as an LCD panel, and the display panel displays information by allowing light irradiated from the optical sheet  205  to pass therethrough. 
     The display panel  207  comprises transparent substrates, which face each other, and a liquid crystal layer interposed between the transparent substrates. The display panel  207  adopts an FSC (Field Sequential Color) scheme, in which an image signal is obtained by allowing red light, green light and blue light to pass through the transparent substrate, without using a color filter. If the display panel  207  adopts the FSC-scheme, a single main frame is divided into three sub-frames of red, green and blue, in which data access, response of liquid crystal and light transmission are sequentially performed in each sub-frame similarly to those of the single main frame. 
     The light emitting unit  210  is disposed on an incident surface of the light guide plate  203 , and sequentially emits red light, green light and blue light. The three-color light is sequentially incident into the light guide plate  203 . 
     The light emitting unit  210  comprises a substrate  220  and a light emitting diode  230 . A driving circuit  250  is disposed at a side of the substrate  220 , and sequentially receives the two control signals S 1  and S 2  from a driver  240 . 
     A plurality of light emitting diodes  230  are disposed on a surface of the substrate  220  in the form of an array, and a red LED chip, a blue LED chip and a green LED chip are mounted on each light emitting diode in the form of a package. The three color LED chips may be mounted on a single diode in the form of a package, or may be separately mounted on the red LED, blue LED and green LED, respectively. 
     The LED chips of the light emitting diodes  230  are turned on/off by the driving circuit  250 . The driving circuit  250  has a structure identical to that shown in  FIG. 1 , and three signal lines L 1  are connected to first electrodes of the color LED chips and a ground line L 2  is connected to a second electrode of the LED chips. 
     The driving circuit  250  controls an LED-OFF operation, a red LED-ON operation, a green-ON operation, and a blue LED-ON operation according to a combination of the 2-bit control signals S 1  and S 2  such that red/green/blue light is sequentially output to the FSC-type display panel  207 . 
     The driving circuit  250  controls ON/OFF operations of the color LED chips of the light emitting diode  230  based on a logical combination and a sequence of the two control signals S 1  and S 2 . The driving circuit  250  can be connected to the light emitting diodes  230  through the three signal lines L 1  and the ground line L 2 , thereby simplifying a circuit structure of the substrate  220 . 
     According to the FSC-type display device  200 , when the three LED chips are used as a light source, the driving circuit  250  sequentially turns on/off the three color LEDs of the light emitting unit  210  according to the control signals S 1  and S 2  of the driver  240 . 
     The display device  200  having the light emitting unit  210  is applied to a portable phone, a computer or a display device used for a digital broadcasting. 
       FIG. 5  is a perspective view representing a top-view type display device according to the embodiment, and  FIG. 6  is a plan view representing an example of a light emitting unit of  FIG. 5 . 
     As shown in  FIG. 5 , a display device  300  comprises a bottom cover  301 , an optical sheet  305 , a display panel  307 , a light emitting unit  310 , a driver  340  and a driving circuit  350 . The bottom cover  301  is prepared in the form of vessel, and comprises metal such as aluminum, magnesium, zinc, titanium, tantalum, hafnium and niobium. An inner circumference of the bottom cover  301  has a side surface  302 , which has an inclination structure to reflect light. 
     The light emitting unit  310  is disposed in the bottom cover  301  to radiate light in a vertical upward direction. 
     The optical sheet  305  comprises at least one of a diffusion sheet, a prism sheet, and a brightness enhancement film to uniform a brightness of light radiated to the display panel  307 . 
     The light emitting unit  310  comprises substrates  320  and a light emitting diode  330 . A plurality of light emitting diodes  330  are disposed on the substrate  320  in the form of an array. The light emitting diodes  330  are provided as a three color light emitting diode chip (for example, a red/green/blue LED chip) or are separately provided as a color light emitting diode. 
     The driving circuit  350 , which is identical to the driving circuit shown in  FIG. 1 , is disposed at a side of the substrate  320 . The driving circuit  350  sequentially controls an ON/OFF operation of the three color light emitting diode chips according two control signals that are output to the driver  340 . That is, the driving circuit  350  controls the ON/OFF operation of the three color light emitting diodes chips through four signal lines, thereby simplifying a circuit design and ensuring a space for the circuit. The driving circuit  350  is disposed on each of light emitting diodes, is disposed on each of the substrates  320 , or is disposed on a light unit  325 . The light unit  325  comprises the bottom cover  301 , the optical sheet  305  and the light emitting unit  310 . 
     Accordingly, the display panel  307  allows red light, green light and blue light to pass through three sub-frames, respectively such that each sub-frame is operated in the similar mode to that of a main frame of the display  300 , in which a data access, a response of liquid crystals and a light transmission are sequentially performed. If the display panel  207  adopts the FSC-scheme, when the three color LED chips are used as a light source, the three color LED chips can be sequentially operated into ON/OFF operations. 
     As shown  FIG. 6 , a plurality of substrates  320  are arranged in the form of a bar on the light emitting unit  310 , which is disposed in the bottom cover  301 . The driving circuit  350  is disposed at a side of the substrate  320 . The driving circuit  350  sequentially turns on the three color LED chips of the light emitting diode  330  which is mounted on the substrate  320 . 
     Since the driving circuit  350  is disposed on each of the substrates  320 , the driving circuit  350  is connected to the three color LED chips of the light emitting diode  330 , which is disposed on the substrate, through four signal lines. The three color LED chips are sequentially turned on/off by the driving circuit  350 . The driving circuit  350  is disposed at each of the substrates  320  or is individually disposed on the light emitting unit  310 . 
     The display device  300  having the light emitting unit  310  can be applied to a computer or a display device for a digital broadcast. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art. 
     INDUSTRIAL APPLICABILITY 
     According to the embodiment, ON/OFF operations of a red LED, a green LED and a blue LED are controlled by a 2-bit control signal. 
     According to the embodiment, a red LED, a green LED and a blue LED are sequentially turned on/off by a 2-bit control signal. 
     According to the embodiment, two electrodes of three color LEDs are connected through four signal lines, so that a line pattern of a substrate is simplified and a sufficient space is ensured for the substrate. 
     The embodiment provides a control circuit for a light emitting diode, which is applied to the FSC type display device, and a light unit having the same.