Patent Publication Number: US-8531132-B2

Title: Backlight unit, driving method thereof, and error detection method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and benefit of Korean Patent Application No. 10-2010-0004445, filed on Jan. 18, 2010, which is herein incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Exemplary embodiments of the present invention relate to a backlight unit capable of improving error detection with respect to light sources thereof, and a method for driving the backlight unit and providing an error detection of the backlight unit. 
     2. Description of the Related Art 
     A liquid crystal display may include a liquid crystal display panel for displaying an image and a backlight unit of the liquid crystal display panel for providing light to the liquid crystal display panel. Recently, instead of using cold cathode fluorescent lamps, attention to light emitting diodes adopted as light sources of the backlight unit have been increased because the light emitting diodes have various advantages over the conventional fluorescent lamps such as low power consumption and high color reproducibility. 
     If light emitting diodes are adopted as the light sources of the backlight unit, the backlight unit may include a plurality of light source strings connected to each other in parallel and each of the light source strings may include a plurality of light emitting diodes connected to each other in series. As a consequence, the light emitting diodes of the light source strings may encounter a problem that may cause a short circuit or an open circuit. Thus, there is a need for an approach to provide an error detection scheme for a circuit condition. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention provide a backlight unit capable of improving error detection with respect to light sources employed therein. 
     Exemplary embodiments of the present invention provide a method for driving the backlight unit. 
     Exemplary embodiments of the present invention provide a method for providing an error detection of the backlight unit. 
     Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. 
     Exemplary embodiments of the present invention disclose a backlight unit. The backlight unit includes a driving circuit to output a driving voltage. The backlight unit also includes a plurality of light source strings comprising a plurality of light sources disposed to generate a light by driving voltage via an input terminal. The backlight unit includes an error detector coupled to an output terminal of the respective light source strings to receive voltages between the input terminal and the output terminal of the respective light source strings and to detect an error of the light sources by using a first voltage and a second voltage, the first voltage corresponding to a voltage difference between a maximum voltage and a minimum of the received voltages and the second voltage obtained by dividing one of the received voltages by a number of the light sources of a light source string. 
     Exemplary embodiments of the present invention disclose a method for driving a backlight unit. The method includes receiving voltages between input terminals and output terminals of a plurality of light source strings, each of the light source strings comprising a plurality of light sources. The method also includes detecting an error in the light sources by using a first voltage and a second voltage to output an error detection signal, the first voltage corresponding to a voltage difference between a maximum voltage and a minimum voltage of the received voltages and the second voltage obtained by dividing one received voltage of the received voltages by a number of the light sources of a light source string. The method also includes controlling the driving voltage in response to the error detection signal. 
     Exemplary embodiments of the present invention disclose a method for providing an error detection of a backlight unit. The method includes receiving voltages between input terminals and output terminals of a plurality of light source strings, each of the light source strings comprising a plurality of light sources. The method also includes detecting an error in the is light sources by using a first voltage and a second voltage, the first voltage corresponding to a voltage difference between a maximum voltage and a minimum voltage of the received voltages and the second voltage obtained by dividing one of the received voltages by a number of the light sources of a light source string. 
     Exemplary embodiments of the present invention disclose a method. The method includes receiving voltages specifying a voltage with respect to an input and output of a plurality of light sources. The method also includes determining a first voltage and a second voltage, the first voltage corresponding to voltage difference of a maximum voltage and a minimum voltage of received voltages, the second voltage obtained by dividing the received voltages by a number of the plurality of the light sources. The method further includes applying the determined first voltage and the second voltage to monitor an error of the plurality of the light sources. 
     Exemplary embodiments of the present invention disclose an apparatus. The apparatus includes a logic coupled to a processor of an error detector to determine an error of a plurality of light sources by using a first voltage and a second voltage. The first voltage corresponds to voltage difference of a maximum voltage and a minimum voltage of voltages received, and the second voltage is obtained by dividing the received voltages by a number of the plurality of the light sources. The received voltages specify a voltage with respect to an input and an output of the plurality of light sources. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a block diagram illustrating a backlight unit according to exemplary embodiments of the present invention. 
         FIG. 2  is a block diagram illustrating a backlight unit according to exemplary embodiments of the present invention. 
         FIG. 3  is a circuit diagram illustrating a first circuit of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     Advantages and features of the present invention can be understood more readily by reference to the following detailed description of exemplary embodiments and the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that disclosure is thorough, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements. 
     It is understood that when an element or a layer is referred to as being “on” “coupled” or “connected to” another element or layer, it can be directly on or directly connected to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on” “directly coupled” or “directly connected to” is another element or layer, there are no intervening elements or layers present. 
     Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings. 
       FIG. 1  is a block diagram illustrating a backlight unit  100  according to exemplary embodiments of the present invention. 
     Referring to  FIG. 1 , the backlight unit  100  may include a driving circuit  110 , a plurality of light source strings  120 , an error detector  130 , and a control circuit  140 . 
     The light source strings  120  can be connected to each other in parallel and each of the light source strings  120  may include a plurality of light sources  121 , for example, light emitting diodes (LED), which may be connected to each other in series. The light source strings  120  may include a plurality of zener diodes (not shown) and each of the light sources  121  may be connected to at least one of the zener diodes in parallel. 
     The driving circuit  110  may receive an input voltage V in , for example, about 12 volts, from an outside to output a driving voltage V out . An output terminal of the driving circuit  110  may commonly be connected to input terminals of the light source strings  120 . Therefore, each of the light source strings  120  may receive the driving voltage V out . 
     Although not shown in  FIG. 1 , the driving circuit  110  may be a direct current to direct current converter (hereinafter, referred to as DC-DC converter). The driving voltage V out  may be used to drive the light sources  121  of the light source strings  120  and may have a voltage level of about 20 volts to about 35 volts. The voltage level of the driving voltage V out  may depend on the number of the light sources  121  included in one light source string. 
     The error detector  130  may be connected to the output terminal of the driving circuit  110  and output terminals of the light source strings  120  to detect a voltage between the is output terminal of the driving circuit  110  and each output terminal of the light source strings  120 . 
     The error detector  130  can detect an error in the light sources  121  by using a first voltage and a second voltage. The first voltage may be a voltage difference between the maximum and the minimum of the detected voltages and the second voltage may be a detected voltage of the detected voltages, which is obtained by dividing the one detected voltage by the number of the light sources  121  included in the light source string from which the one detected voltage can be detected. In this example, the detected voltage may be the maximum voltage of the detected voltages, but may not be limited thereto. 
     The error detector  130  may electrically be connected to the control circuit  140  and may output an error detection signal S ED  to the control circuit  140  if the first voltage is higher than the second voltage. Alternatively, the error detector  130  may output the error detection signal S ED  to the control circuit  140  if the first voltage is higher than the second voltage to which a predetermined voltage is added. 
     The predetermined voltage may be determined by experimentations and existing theories with respect to characteristic of the light sources  121 . According to exemplary embodiments of the present invention, the relation between the first voltage and the second voltage to output the error detection signal S ED  may be, but not restricted to, an inequation that contains more than one degree variables, for example, the first voltage and the second voltage can be the variables such as an exponential function variable, or a logarithm function variable. 
     The control circuit  140  may be provided in a chip and may be coupled to the error detector  130  and the driving circuit  110 . The control circuit  140  may receive the error detection signal S ED  and output a power control signal CS to the driving circuit  110  in response to the error detection signal S ED  to control the driving voltage V out . For example, the control circuit  140  may is output a power control signal CS to make the driving voltage V out  in lower level or block the output of the driving voltage V out  if the error detection signal S ED  is detected higher than a reference value. 
     In  FIG. 1 , the control circuit  140  and the error detector  130  can be seen separately, but according to exemplary embodiments, the control circuit  140  may include the error detector  130 . 
     In some example, the backlight unit  100  may include a plurality of current control devices Tr 1 ˜Tr n , and first electrodes of the current control devices Tr 1 ˜Tr n  may electrically be coupled to the output terminals of the light source strings  120 , respectively. The control circuit  140  may be coupled to second electrodes and third electrodes of the current control devices Tr 1 ˜Tr n . The control circuit  140  can detect currents of the light source strings  120  from the third electrodes of the current control devices Tr 1 ˜Tr n  and can output current control signals S 1 ˜S n  to the second electrodes of the current control devices Tr 1 ˜Tr n  in response to receipt of the detected current values I s1 ˜I sn  and the error detection signal S ED  to control currents flowing through the light source strings  120 . 
     In some examples, the control circuit  140  may not be coupled to the third electrodes of the current control devices Tr 1 ˜Tr n . In this example, the control circuit  140  may output the current control signals S 1 ˜S n  that control currents flowing through the light source strings  120  to the second electrodes of the current control devices Tr 1 ˜Tr n  in response to receipt of the error detection signal S ED . The error detection signal S ED  may include a signal that indicates the existence of errors and a signal that indicates voltages of the light source strings  120 . 
     In some examples, the control circuit  140  may directly be coupled to the output is terminals of the light source strings  120  to detect the voltages and the currents of the light source strings  120  and may output the current control signals S 1 ˜S n  according to the detected result. 
     The backlight unit  100  may include a plurality of resistors R s1 ˜R Sn  each of which may be coupled between one of the third electrodes of the current control devices Tr 1 ˜Tr n  and ground. 
       FIG. 2  is a block diagram illustrating a backlight unit  200  according to exemplary embodiments of the present invention. In  FIG. 2 , the same reference numerals may denote the same elements in  FIG. 1 , and thus detailed descriptions of the same elements may be omitted in order to avoid unnecessarily obscuring the invention. 
     The backlight unit  200  may include the driving circuit  110 , the light source strings  120 , the control circuit  140 , a plurality of first diodes D 11 ˜D 1n , a plurality of second diodes D 21 ˜D 2n , a first resistor R 1 , a second resistor R 2 , a first circuit  231 , a second circuit  233 , and a comparison circuit  235 . 
     Anode terminals of the first diodes D 11 ˜D 1n  may be coupled to the output terminals of the light source strings  120 , respectively. In this example, the maximum voltage V max  of the light source strings  120  can be output through the cathode terminals of the first diodes D 11 ˜D 1n . 
     Cathode terminals of the second diodes D 21 ˜D 2n  may be coupled to the output terminals of the light source strings  120 , respectively. In this example, the minimum voltage V min  of the light source strings  120  can be output through the anode terminals of the second diodes D 21 ˜D 2n . 
     A terminal of the first resistor R 1  may be coupled to the input terminals of the light source strings  120 . 
     The second resistor R 2  may be coupled between the first resistor R 1  and the cathode terminals of the first diodes D 11 ˜D 1n . 
     According to the configuration of the second circuit  233 , resistances of the first resistor R 1  and the second resistor R 2  can be selected to allow the second circuit  233  to output a second voltage V 2  that is obtained by dividing the maximum voltage V max  by the number of the light sources  121  of a light source string from which the maximum voltage V max  is detected. Preferably, the resistances of the first resistor R 1  and the second resistor R 2  may be much higher than the resistance of each of the light source strings  120 , thereby minimizing currents flowing through the first resistor R 1  and the second resistor R 2 . 
     A first terminal of the first circuit  231  may be coupled to the cathode terminals of the first diodes D 11 ˜D 1n  and a second terminal of the first circuit  231  may be coupled to the anode terminals of the second diodes D 21 ˜D 2n . The first circuit  231  can receive the maximum voltage V max  and the minimum voltage V min  respectively via the first terminal and the second terminal to output a first voltage V 1  corresponding to a voltage difference between the maximum voltage V max  and the minimum voltage V min . 
     A first terminal of the second circuit  233  may be coupled to the cathode terminals of the first diodes D 11 ˜D 1n  and a second terminal of the second circuit  233  may be coupled to a node at which the first resistor R 1  and the second resistor R 2  are coupled to each other. The second circuit  233  may receive the maximum voltage V max  and a division voltage of the node at which the first resistor R 1  and the second resistor R 2  are coupled to each other through the first terminal and the second terminal, respectively, to output the second voltage V 2  that is obtained by dividing the maximum voltage V max  by the number of the light sources  121  of a light source string from which the maximum voltage V max  is detected. 
     A terminal of the comparison circuit  235  may be coupled to the output terminal of the first circuit  231  and another terminal of the comparison circuit  235  may be coupled to the output terminal of the second circuit  233 . The comparison circuit  235  can receive the first voltage V 1  and the second voltage V 2  and can compare the first voltage V 1  and the second voltage and V 2  to detect an error in the light sources  121 . The comparison circuit  235  may be a circuit, for example, a differential amplifier, which is capable of comparing two voltages, or a circuit similar to the first circuit  231  or the second circuit  233 . 
     The comparison circuit  235  may output an error detection signal S ED  to the control circuit  140  if the first voltage V 1  is higher than that of the second voltage V 2 . The control circuit  140 , which may be coupled to the comparison circuit  235  to receive the error detection signal S ED , outputs a power control signal CS to the driving circuit  110  in response to receipt of the error detection signal S ED  to control the driving voltage V out . Also, the control circuit  140  may output current control signals S 1 ˜S n  to the current control devices Tr 1 ˜Tr n  to control currents flowing through the light source strings  120 . 
     In some examples, the comparison circuit  235  may output the error detection signal S ED  to the control circuit  140  if the first voltage V 1  is has higher than the second voltage V 2  to which a predetermined voltage is added. The control circuit  140  may be coupled to the comparison circuit  235  to receive the error detection signal S ED  and to output the power control signal CS to the driving circuit  110  in response to receipt of the error detection signal S ED  that controls the driving voltage V out . Also, the control circuit  140  may output the current control signal S 1 ˜S n  to the current control devices Tr 1 ˜Tr n  to control currents flowing through the light source strings  120 . 
     Although not shown in  FIG. 2 , the first terminal of the second circuit  233  may is alternately be coupled to the anode terminals of the second diodes D 21 ˜D 2n . Also, the second resistor R 2  may alternately be coupled between the first resistor R 1  and the anode terminals of the second diodes D 21 ˜D 2n . In this alternative example, the second circuit  233  can receive the minimum voltage V min  to output a second voltage V 2  that is obtained by dividing the minimum voltage V min  by the number of the light sources  121  of a light source string from which the minimum voltage V min  is detected. 
     In some examples, the relation between the first voltage V 1  and the second voltage V 2  to output the error detection signal S ED  may be, but not restricted to, an inequation that contains more than one degree variables, for example, the first voltage and the second voltage can be the variables such as an exponential function variable, or a logarithm function variable. 
       FIG. 3  is a circuit diagram illustrating a first circuit  231  of  FIG. 2 . The first circuit illustrated in  FIG. 3  may be an example and may be any circuit known as differential amplifiers can be used. 
     The first circuit  231  may include a first operational amplifier (hereinafter referred to as ‘OP amplifier’) OP 1 , a second OP amplifier OP 2 , a third OP amplifier OP 3 , two third resistors R 3 , two fourth resistors R 4 , a fifth resistor R 5 , and two sixth resistors R 6 . 
     A positive (+) terminal of the first OP amplifier OP 1  may be coupled to the anode terminals of the second diodes D 21 ˜D 2n  to receive the minimum voltage V min  and a positive terminal of the second OP amplifier OP 2  may be coupled to the cathode terminals of the first diodes D 11 ˜D 1n  to receive the maximum voltage V max . 
     The fifth resistor R 5  may be coupled between a negative (−) terminal of the first OP amplifier OP 1  and a negative terminal of the second OP amplifier OP 2 . 
     One of the sixth resistors R 6  may be connected between the negative terminal and is an output terminal of the first OP amplifier OP 1  and the other of the sixth resistors R 6  may be connected between the negative terminal and an output terminal of the second OP amplifier OP 2 . 
     One of the third resistor R 3  my be coupled between the output terminal of the first OP amplifier OP 1  and a negative terminal of the third OP amplifier OP 3  and the other of the third resistor R 3  may be coupled between the output terminal of the second OP amplifier OP 2  and a positive terminal of the third OP amplifier OP 3 . 
     One of the fourth resistors R 4  may be coupled between the positive terminal of the third OP amplifier OP 3  and ground, and the other of the fourth resistor R 4  may be coupled between an output terminal and the negative terminal of the third OP amplifier OP 3 . 
     The relation between the first voltage V 1  output from the first circuit  231  and the minimum and maximum voltages V min  and V max  input to the first circuit  231  can satisfy Equation 1 below. 
     
       
         
           
             
               
                 
                   
                     V 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   = 
                   
                     
                       
                         
                           R 
                           4 
                         
                         ⁡ 
                         
                           ( 
                           
                             1 
                             + 
                             
                               
                                 R 
                                 4 
                               
                               
                                 R 
                                 3 
                               
                             
                           
                           ) 
                         
                       
                       ⁢ 
                       
                         ( 
                         
                           
                             V 
                             max 
                           
                           - 
                           
                             V 
                             min 
                           
                         
                         ) 
                       
                     
                     
                       R 
                       3 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     In this example, resistances of the third resistor R 3  and fourth resistor R 4  can be selected to satisfy Equation 2 below. 
     
       
         
           
             
               
                 
                   
                     
                       
                         R 
                         4 
                       
                       ⁡ 
                       
                         ( 
                         
                           1 
                           + 
                           
                             
                               R 
                               4 
                             
                             
                               R 
                               3 
                             
                           
                         
                         ) 
                       
                     
                     
                       R 
                       3 
                     
                   
                   = 
                   1 
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
           
         
       
     
     Although not shown in figures, the second circuit  233  of  FIG. 2  may be a circuit that is similar to the first circuit  231  of  FIG. 3  or a different circuit having the same function. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.