Abstract:
There is provided a driving circuit for a backlight unit having a reset function to prevent a malfunction of an apparatus caused by electrical stress such as ESD/EOS. A driving circuit for a backlight unit according to an aspect of the invention may include: a power supply section supplying driving power; a control section receiving the driving power from the power supply section to control the luminance of lamps; and a reset section detecting a voltage level of a luminance control signal from the control section to reset the driving power supplied to the control section when the control section malfunctions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 2008-0083073 filed on Aug. 25, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to driving circuits for backlight units, and more particularly, to a driving circuit for a backlight unit having a reset function to prevent a malfunction of an apparatus caused by electrical stress such as ESD/EOS. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, among display devices, liquid crystal displays (LCDs) have been used in various kinds of products including computers, notebook computers, and AV devices, since they have advantages such as small size, light weight and low power consumption. 
         [0006]    Backlight units that emit light necessary for pixels are used in these LCDs. 
         [0007]    Each of the backlight units includes a plurality of bar-shaped lamps, a power supply circuit supplying power to the lamps and driving power to another circuit, and a control unit receiving the driving power to control the luminance of each lamp. 
         [0008]    Cold cathode fluorescent lamps (CCFLs) are generally used as the above lamps. However, backlight units using light emitting diodes as light sources have appeared in consideration of processing speed, power consumption and life. 
         [0009]    The backlight unit using the light emitting diodes as light sources includes a driving circuit to control the light emitting diodes. The above-described driving circuit uses a control section formed of a field-programmable gate array (FPGA) to perform local dimming and scanning dimming. The driving circuit having the FPGA can maximize a contrast ratio and effectively remove an afterimage of a moving image. 
         [0010]    However, the control section formed of the FPGA is susceptible to electrical stress such as electro-static discharge (ESD) or electrical over stress (EOS). When the electrical stress is applied to the control section, a failure occurs in the control section. 
       SUMMARY OF THE INVENTION 
       [0011]    An aspect of the present invention provides a driving circuit for a backlight unit having a reset function to prevent a malfunction of an apparatus caused by electrical stress such as ESD/EOS. 
         [0012]    According to an aspect of the present invention, there is provided a driving circuit for a backlight unit, the driving circuit including: a power supply section supplying driving power; a control section receiving the driving power from the power supply section to control the luminance of lamps; and a reset section detecting a voltage level of a luminance control signal from the control section to reset the driving power supplied to the control section when the control section malfunctions. 
         [0013]    The reset section may include: a detection unit detecting whether a signal level of the luminance control signal from the control section is within a predetermined level range; and a reset control unit cutting off supply of the driving power for a predetermined period of time when a result of the detection from the detection unit indicates a malfunction. 
         [0014]    The detection unit may include: a first comparator having a first plus input terminal receiving a predetermined first reference voltage and a first minus input terminal receiving the luminance control signal; and a second comparator having a second plus input terminal receiving the luminance control signal and a second minus input terminal receiving a second reference voltage having a higher voltage level than the first reference voltage. 
         [0015]    The reset section further may include a switch unit switching bias power having a predetermined voltage level from the power supply section and transmitting a high-level signal when a result of the detection from the detection unit indicates a malfunction, and the switch unit may include: a first switch switched on to open a path through which the bias power is transmitted to a ground; and a second switch blocking the path through which the bias power is transmitted to the ground and transmitting a high-level signal to the reset control unit when the first switch is switched on. 
         [0016]    The reset control unit may include: a pulse generator outputting a pulse signal having a predetermined time duration when the high-level signal is transmitted from the second switch; and a third switch cutting off supply of the driving power during a time when the pulse signal from the pulse generator maintains a high level. 
         [0017]    The control section may include: a main controller outputting a pulse width modulation (PWM) luminance control signal to perform local control of the luminance of the lamps and a linear luminance control signal to determine a signal level of the PWM luminance control signal; and an auxiliary controller outputting a PWM luminance control signal to perform local control of the luminance of the lamps. 
         [0018]    The main controller may transmit a predetermined pulse signal to the auxiliary controller, and output the linear luminance control signal when receiving a response signal to the pulse signal from the auxiliary controller. 
         [0019]    The control section further may include a filter for filtering the linear luminance control signal from the main controller to transmit the filtered luminance control signal to the detection unit of the reset section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0021]      FIG. 1  is a schematic view illustrating a configuration of a driving circuit for a backlight unit according to an exemplary embodiment of the invention; and 
           [0022]      FIG. 2  is a detailed view illustrating a reset section used in a driving circuit for a backlight unit according to an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0024]      FIG. 1  is a schematic view illustrating a configuration of a driving circuit for a backlight unit according to an exemplary embodiment of the invention. 
         [0025]    Referring to  FIG. 1 , a driving circuit  100  for a backlight unit according to an exemplary embodiment of the invention includes a power supply section  110 , a control section  120 , and a reset section  130 . 
         [0026]    The power supply section  110  converts input power Vin into a plurality of powers having different voltage levels. That is, the power supply section  110  may output enable power and driving power having different voltage levels. As shown in  FIG. 2 , the power supply section  110  may output bias power. 
         [0027]    The enable power and the driving power from the power supply section  110  are transmitted to the control section  120 . 
         [0028]    The control section  120  outputs a luminance control signal to control the luminance of lamps. Here, when the enable power from the power supply section  110  has a high voltage level, the control section  120  starts to operate, and performs the luminance control operation when receiving the driving power required to perform this operation. 
         [0029]    The control section  120  can perform local luminance control so that the luminance of some of the plurality of lamps can be controlled. The control section  120  outputs a pulse width modulation (PWM) luminance control signal for the local luminance control and a linear luminance control signal to determine a level size of the PWM luminance control signal. Here, the linear luminance control signal means a current target value when the PWM luminance control signal has a duty cycle of 100%. 
         [0030]    The control section  120  may include a main controller  121  and an auxiliary controller  122 , and may also include a filter  123 . 
         [0031]    Each of the main controller  121  and the auxiliary controller  122  may be a digital integrated circuit (IC) formed of a field-programmable gate array (FPGA), and thus may be susceptible to electrical stress. The main controller  121  sends a pulse signal to the auxiliary controller  122  at regular time intervals. When the main controller  121  receives a response signal to the pulse signal from the auxiliary controller  122 , the main controller  121  determines that the auxiliary controller  122  performs a normal operation, and then outputs the linear luminance control signal. 
         [0032]    The linear luminance control signal is filtered through the filter  123  and sent to the reset section  130 . 
         [0033]    The reset section  130  may include a detection unit  131 , a switch unit  132 , and a reset control unit  133 . 
         [0034]    The detection unit  131  receives the luminance control signal from the filter  123  and detects whether the luminance control signal is normal or abnormal. That is, when the auxiliary controller  122  of the control section  120  malfunctions due to electrical stress, the main controller  121  does not output the linear luminance control signal. When a failure occurs in the main controller  121 , the linear luminance control signal has a low or high voltage level. 
         [0035]    Therefore, when the luminance control signal has a voltage level within a predetermined reference voltage range, the detection unit  131  determines that the control section  120  performs a normal operation. When the luminance control signal has a voltage level outside the reference voltage range, the detection unit  131  determines that a failure occurs in the control section  120 , and detects whether the control section  120  malfunctions or not. 
         [0036]    When a detection result from the detection unit  131  indicates a malfunction, the switch unit  132  switches the bias power from the power supply section  110  to output a high-level signal. On the other hand, when the detection result indicates a normal operation, the switch unit  132  outputs a low-level signal. 
         [0037]    When the reset control unit  133  receives the high-level signal from the switch unit  132 , the reset control unit  133  cuts off supply of the driving power for a predetermined period of time to reset the control section  120 . 
         [0038]      FIG. 2  is a detailed view illustrating a reset section used in a driving circuit for a backlight unit according to an exemplary embodiment of the invention. 
         [0039]    Referring to  FIGS. 1 and 2 , the detection unit  131  may include a first IC U 1  having first and second comparators. For example, the detection unit  131  may be formed of an LM324 IC. 
         [0040]    The first IC U 1  may have fourteen terminals and four comparators. Among them, two of the comparators corresponding to first through seventh terminals located on the left side of the first IC U 1  may form a predetermined buffer circuit, and an internal circuit corresponding to eighth to fourteenth terminals located on the right side of the first IC U 1  may form the first and second comparators. A first reference voltage of approximately 1.0V is supplied to the tenth terminal, which is a plus terminal of the first comparator. A second reference voltage of approximately 3.0V is supplied to the thirteenth terminal, which is a minus terminal of the second comparator. The voltage level of the luminance control signal from the control section  120  is input to each of the ninth terminal, which is a minus terminal of the first comparator, and the twelfth terminal, which is a plus terminal of the second comparator. 
         [0041]    When the luminance control signal has a voltage level within the first reference voltage range and the second reference voltage range, it is determined that the control section  120  performs a normal operation. When the luminance control signal has a voltage level outside the first reference voltage range and the second reference voltage range, it is determined that the control section  120  performs an abnormal operation. 
         [0042]    That is, the detection unit  131  detects whether a failure occurs in the control section  120 , and transmits a detection result to the switch unit  132 . Here, since the detection unit  131  includes the above-described first and second comparators, the detection result is output as a high-level signal when the control section  120  malfunctions. 
         [0043]    The switch unit  132  receives bias power having a predetermined voltage level from the power supply section  110 . The switch unit  132  includes first and second switches SW 1  and SW 2  that are connected in parallel between a bias power terminal and a ground terminal. 
         [0044]    When the detection result from the detection unit  131  indicates a malfunction, that is, a high-level signal, the detection result is transmitted to a base of the first switch SW 1 . Then, the first switch SW 1  is switched on to open a path through which the bias power is transmitted to the ground. 
         [0045]    When the first switch SW 1  is switched on, a low-level signal is transmitted to a base of the second switch SW 2  such that the second switch SW 2  is switched off to thereby block the path through which the bias power is transmitted to the ground. The second switch SW 2  transmits the high-level signal to the reset control unit  133 . The voltage level of the bias power may be equal to that of the high-level signal from the second switch SW 2 . 
         [0046]    The reset control unit  133  includes a pulse generator U 2  that outputs a predetermined pulse signal and a third switch SW 3  that outputs a reset signal. 
         [0047]    The pulse generator U 2  outputs a pulse signal having a predetermined time duration when receiving the high-level signal from the second switch SW 2 . The pulse generator U 2  may be formed of a 555 timer or an integrated circuit having eight terminals. The high-level signal from the second switch SW 2  is input to a fourth terminal, and the pulse signal may be correspondingly output through a third terminal. 
         [0048]    The third switch SW 3  outputs a reset signal during a time when the pulse signal from the pulse generator U 2  maintains a high level. 
         [0049]    That is, when the pulse signal from the pulse generator U 2  has a high level, the third switch SW 3  cuts off the supply of the driving power supplied to the control section  120  from the power supply section  110  to thereby reset the control section  120 . 
         [0050]    As set forth above, according to an exemplary embodiment of the invention, a malfunction of a digital IC, such as an FPGA, can be prevented even when electrical stress is applied to a backlight unit. 
         [0051]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.