Patent Publication Number: US-2016249427-A1

Title: Led backlight source used in lcd devcice and lcd device therefore

Description:
FIELD OF THE INVENTION 
     The present invention relates to the LCD technical field; in particular, to a LED backlight source used in a LCD device and the LCD device. 
     BACKGROUND OF THE INVENTION 
     As technology advances, the LCD backlight technology and equipment continue to be developed. The conventional LCD backlight device used cold cathode fluorescent lamps (CCFL) for displaying images; however, due to the disadvantages of CCFL backlight: poor color reproduction capability, low luminous efficiency, high discharge voltage, discharge characteristics at low temperature difference, long time for heating to stable gray and so on, the LED backlight source of the technical backlight source has been invented nowadays 
     In the traditional LED backlight sources, the LED forward current has a positive correlation with the on-voltage of the LED, i.e. the forward current is larger and the on-voltage of the LED is larger as well. In order to modulate the forward current when the LED is illuminated, the on-voltage of the LED has to be modulated quickly at the same time. However, the speed of the traditional modulation is low; the LEDs in the backlight source have a flicker problem. The LED driver chip has a malfunction about LED short protection when the problem gets worse. 
     SUMMARY OF THE INVENTION 
     In order to solve the problem existing in the traditional art, one of the goals of the present invention is to provide a LED backlight source used in an LCD device comprising: a boost circuit, configured to boost an input voltage to an operating voltage of an LED string; a current control module, configured to connect to a negative end of the LED string for modulating the operating voltage of the LED string; a microcontroller, configured to provide the current control module with the second square wave signal to control the current control module for achieving current modulation; a boost driver chip, configured to provide the boost circuit with a first square wave signal to the boost circuit for achieving voltage boost function; the boost driver chip receives a feedback regulation voltage found by the microcontroller and changes a duty ratio of the first square wave signal provided by the boost circuit according to the feedback regulation voltage, for modulating the operating voltage of the LED string. 
     The other one of the goals of the present invention is to provide an LCD device comprising an LCD panel and a LED backlight source in opposite to the LCD panel, wherein the LED backlight source provides light with the LCD panel so that the LCD displays images, wherein the LED backlight source comprises: a boost circuit, configured to boost an input voltage to an operating voltage of an LED string; a current control 
     module, configured to connect to a negative end of the LED string for modulating the operating voltage of the LED string; a microcontroller, configured to provide the current control module with a second square wave signal to control the current control module for achieving current modulation; a boost driver chip, configured to provide the boost circuit with a first square wave signal to the boost circuit for achieving voltage boost function; the boost driver chip receives a feedback regulation voltage found by the microcontroller and changes a duty ratio of the first square wave signal provided by the boost circuit according to the feedback regulation voltage, for modulating the operating voltage of the LED string. 
     Further, the boost circuit comprises an inductor, a first MOS transistor, and a rectifier diode, wherein an end of the inductor is used for receiving the input voltage, the other end of the inductor connects to a positive electrode of the rectifier diode and an drain of the first MOS transistor, a negative electrode of the rectifier diode connects to a positive end of the LED string, a gate of the first MOS transistor connects to a square wave signal output end of the boost driver chip, a source of the first MOS transistor is electrically grounded. 
     Further, the current control module comprises a second MOS transistor and a forth resistor, wherein a gate of the second MOS transistor connects to an LED operating current control end of the microcontroller, a drain of the second MOS transistor connects to a negative end of the LED string, a source of a third MOS transistor connects to an end of the forth resistor, the other end of the forth resistor is electrically grounded. 
     Further, the LED backlight source further comprises a first resistor, a second resistor and a third resistor, wherein an end of the first resistor connects to a positive end of the LED string; an end of the second resistor is electrically grounded; an end of the third resistor connects to a feedback regulation voltage output end of the microcontroller; the other end of the first resistor, the other end of the second resistor and another end of the third resistor all connect to a feedback regulation voltage input end of the microcontroller. 
     Further, the LED string comprises a predetermined number of serially connected LEDs 
     In light of the LED backlight source used in the LCD device and the LCD device of the present invention, because the microcontroller can find out the corresponding feedback regulation voltage quickly based on the operating current of the LED string from the lookup table, it can modulate the operating voltage provided by the boost circuit rapidly so that the operating voltage of the LED string can be regulated quickly while the operating current of the LD string  150  is also regulated. The LEDs of the LED string avoid a flicker issue and at the same time the microcontroller  130  avoids the malfunction for protection of the short LEDs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description taken in conjunction with the above and other objects, features and advantages of the present invention will become more apparent. The figures: 
         FIG. 1  is a structural diagram of the LCD device according to the embodiment of the present invention; 
         FIG. 2  is a block diagram of the LCD backlight source used in the LCD device according to the embodiment of the present invention; 
         FIG. 3  is a circuit diagram of the LCD backlight source used in the LCD device according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, the drawings will be described a preferred embodiment of the present invention reference. However, the present invention can be implemented in many different forms and should not be construed as limited to the exemplary embodiments set forth embodiment. In addition, as described in this term taking into account the features of the invention can be defined differently depending on the intent and practice of the use of the user and the operator. Therefore, it should be based on the disclosure of the specification to understand these terms. On the contrary, the present invention is intended to cover not only the exemplary embodiments, but also covers defined by the claims in the present invention, the spirit and scope of the various alternatives, modifications, equivalents and other embodiments. 
       FIG. 1  is the structural diagram of the LCD device according to the embodiment of the present invention. 
     Refer to  FIG. 1 . Based on the embodiment of the present invention, the LCD device comprises a LCD panel  200  and a LED backlight source  100  which are in opposite to each other, where the LED backlight source  100  provides light source for the LCD panel  200  so that the LCD panel  200  displays the images. 
     In the following description, the LED backlight source  100  is narrated based on the embodiment of the present invention. 
       FIG. 2  is the block diagram of the LED backlight source used in the LCD device based on the embodiment of the present invention;  FIG. 3  is the circuit diagram of the LED backlight source used in LCD device based on the embodiment of the present invention. 
     Please refer to  FIG. 2  and  FIG. 3 . The LED backlight source based on the present invention comprises: a boost circuit  110 , a current control module  120 , a micro control unit (called MCU for short)  130 , a boost driver chip (IC)  140  and a LED string  150 . 
     Specially, the boost circuit  110  can be an inductive boost circuit used in boosting an inputting voltage V in  into an operating voltage for the LED string  150 . The boost circuit  110  comprises an inductor  111 , a first MOS transistor  112 , and a rectifier diode  113 . In the present embodiment, one end of the inductor  111  is used for receiving the input voltage Vin and the other end of the inductor  111  connects to the positive electrode of the rectifier diode  113  and a drain of the first MOS transistor  112 . The negative electrode of the rectifier diode  113  connects to the positive end of the LED string  150 . The gate of the first MOS transistor  112  connects to the square wave signal output end (DRV) of the boost driver chip  140 . The source of the first MOS transistor is electrically grounded. It should be understood that the boost circuit is not limited in the circuit configuration of the boost circuit  10  in  FIG. 3 . It can be another suitable circuit configuration of the boost circuit. 
     In the boost circuit  110 , the inductor  11  is an energy conversion device which is between the electricity and magnetic field. When the gate of the first MOS transistor  112  receives the high-level signal of the first square wave signal PWM 1  provided by the square wave signal wave output end (DRV) of the boost driver chip  140 , the inductor  111  transforms the magnetic field into the electricity and saves it. Then, the electricity is superposed with the input voltage Vin, the rectifier diode  113  filters the signal and a DC voltage is obtained after the gate of the first MOS transistor  112  receives the high-level signal of the first square wave signal PWM 1  provided by the square wave signal wave output end (DRV) of the boost driver chip  140 . Because the DC voltage is formed by the electricity conversed from the magnetic field of the inductor  111  superposing with the input voltage Vin, the DC voltage is higher than the input voltage Vin. 
     The LED string  150  is used as a backlight source of the LCD device, where the LED string  150  comprises a predetermined number of serially connected LEDs. The LED string  150  receives the operating voltage which it requires for work normally. The LED amount N (N is an integer and larger than zero) of the LED string is made sure by the following rule: 
         N×Vd≦V   out , 
     Where, V d  is a voltage for normal emission of each LED, and V out  is the operating voltage received from the boost circuit and required for work normally. 
     For example, when V d  is 6.5V and Vout=48V, N≦7. 
     The current control module  120  connects to the negative end of the LED string  150  for modulating the operating current of the LED string. The current control module  120  comprises the second MOS transistor  121  and the forth resistor  122 , where the gate of the second MOS transistor  121  connects to the LED operating current control end (LIN) of the microcontroller  130  and the drain of the second MOS transistor  121  connects to one end of the forth resistor  122 . The other end of the forth resistor  122  is electrically grounded. 
     The gate of the third MOS transistor  121  receives the second square wave signal PWM 2  provided by the LED operating control end (LIN) of the microcontroller  130 . The microcontroller  130  enlarges or reduces the operating current of the LED string  150  via modulating the duty ratio of the second square wave signal PWM 2 . Based on the embodiment of the present invention, the operating current of the LED string  150  is usually stable. The microcontroller finds out the feedback regulation voltage from its lookup table based on the operating current of the LED string  150 . The lookup table is set in the microcontroller  130 . The feedback regulation voltage output end (DAC) of the microcontroller  130  connects to the feedback regulation voltage input end (FB) of the boost driver chip  140  through the third resistor  163 . The boost driver chip  140  receives the feedback modulating voltage based on the feedback regulation voltage input end (FB) and changes the duty ratio of the first square wave signal PWM 1  provided by the square wave output end (DRV) and then modulates the operating voltage provided for the LED string  150  by the boost circuit  110 . 
     Otherwise, one end of the first resistor  161  connects to the positive end of the LED string  150 . One end of the second resistor  162  is electrically grounded. The other ends of the first resistor  161  and the second resistor  162  both connect to the feedback regulation voltage input end (FB) of the boost drive chip  140 . 
     In the following description, the relation between the operating current of the LED string  150  and the feedback regulation voltage of the feedback regulation voltage output end (DAC) of the microcontroller is narrated. 
     In the present embodiment, the relation between the operating current of the LED string  150  and the feedback regulation voltage of the feedback regulation voltage output end (DAC) of the microcontroller can be indicated in the following formula (1) 
     
       
         
           
             
               
                 
                   
                     V 
                     LED 
                   
                   = 
                   
                     
                       
                         V 
                         FB 
                       
                       × 
                       
                         ( 
                         
                           
                             
                               R 
                               1 
                             
                             
                               R 
                               3 
                             
                           
                           + 
                           
                             
                               R 
                               1 
                             
                             
                               R 
                               2 
                             
                           
                           + 
                           1 
                         
                         ) 
                       
                     
                     - 
                     
                       
                         V 
                         DAC 
                       
                       × 
                       
                         
                           R 
                           1 
                         
                         
                           R 
                           3 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Where, VLED represents the operating voltage of the LED string  150 , VDAC represents the feedback regulation voltage outputted by the feedback regulation voltage output end (DAC) of the microcontroller  130 . VFB represents the feedback regulation voltage received from the feedback regulation voltage input end (FB) of the boost driver chip  140 , R 1  represents the resistor value of the first resistor  161 , R 2  represents the resistor value of the second resistor  162  and R 3  represents the resistor value of the third resistor  163 . 
     Because the operating current of the LED string  150  is proportional to the operating voltage of the LED string  150 , and the operating voltage of the LED string  150  is inversely proportional to the feedback regulation voltage of the feedback regulation voltage output end (DAC) of the microcontroller, the operating current of the LED string  150  is inversely proportional to the feedback regulation voltage of the feedback regulation voltage output end (DAC) of the microcontroller. Therefore, based on the inverse proportional relation, the lookup table of the operating current of the LED string  150  and the feedback regulation voltage of the feedback regulation voltage output end (DAC) of the microcontroller, can be set up in the microcontroller  130 . In the lookup table, a current value of the operating current of the LED string  150  corresponds to the feedback regulation voltage of the feedback regulation voltage output end (DAC) of the microcontroller. 
     In summary, because the microcontroller  130  can find out the corresponding feedback regulation voltage quickly based on the operating current of the LED string from the lookup table, it can modulate the operating voltage of the boost circuit  110  and provide it for the LED string rapidly so that the operating voltage of the LED string  150  can be regulated quickly while the operating current of the LED string  150  is also regulated. The LEDs of the LED string avoid a flicker issue and at the same time the microcontroller  130  avoids the malfunction for protection of the short LEDs. 
     Although certain exemplary embodiments with reference to the present invention is shown and described the present invention, those skilled in the art should be appreciated that without departing from the spirit and scope of the appended claims and their equivalents of the present invention Next, in form and details may present invention may be variously changed.