Patent Publication Number: US-7212187-B2

Title: Power control apparatus for a display device and method of controlling the same

Description:
This application claims the benefit of Korean Patent Application No. 2003-84784, filed Nov. 27, 2003, which is hereby fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device and, more specifically, to a power control apparatus of a display device that measures an output current to a display panel and adjusts a power supply voltage and a cathode voltage to maintain the output current within designated conditions, thus preventing damage to the display panel due to excessive current and deterioration. 
     2. Discussion of the Related Art 
     Recently, portable electronic devices, such as portable handsets, notebooks, personal computers and personal data assistants, have become widely used. A display device, such as a liquid crystal display (LCD) or an electroluminescence (EL) display, is typically used as the display device in these portable electronic devices due to their low power consumption. The organic EL display and the LCD, which uses an organic EL device as a light emitting source, arrange, drive and control a plurality of display pixels by turning them on or off to display a desired image. Generally, the display device drives the pixels by supplying a power supply voltage and a cathode voltage to the panel. Typically, a low voltage power supply of 2.8˜3.3V is used to drive the panel. A DC-DC converter raises the power supply voltage to +5V or reduces it to −6V and outputs that voltage to the display device. 
       FIG. 1  is a block diagram of a conventional display device. 
     A data driver  10  outputs a data signal to a pixel  51 , a scan driver  20  outputs a selection signal to the pixel  51 , a DC-DC converter  30  raises or reduces an input power supply voltage to output to the pixel  51 , a control unit  40  controls each component, a panel  50  displays a certain image, and the pixel  51  displays a certain color on the panel  50 . 
     As shown in  FIG. 1 , the panel  50  has a plurality of scan lines S 1  . . . S m  and a plurality of data lines D 1  . . . D z , arranged in rows and columns and connected to the scan driver  20  and the data driver  10 , respectively. A plurality of pixels  51  are arranged at their intersections. Further, each pixel  51  is connected to a first level of power supply voltage line  52  and a second level of power supply voltage line  53 , which are connected to the DC-DC converter  30 . Further, the DC-DC converter  30  is connected to the control unit  40 , and the control unit  40  is also connected to the scan driver  20  and the data driver  10 . 
     For the conventional display device with the above configuration, when the control unit  40  transmits a driving control signal to the DC-DC converter  30 , the DC-DC converter  30  raises or reduces the provided power supply voltage (not shown) to apply, for example, +5V to the first level of power supply voltage line  52  and −6V to the second level of power supply voltage line  53 . 
     Further, the control unit  40  applies the driving control signal to the scan driver  20  and the data driver  10 . The scan driver  20  outputs the selection signal to the pixel  51  through the appropriate scan line S 1  . . . S m , and the data driver  10  outputs a light emitting data signal to the pixel  51  through the appropriate data line D 1  . . . D z . 
     Therefore, each pixel  51  is turned on by the selection signal, and a certain color is emitted according to the data signal and the driving signal by the power supply voltage VDD and the cathode voltage VSS, so that the panel  50  displays the desired image. 
     However, the display device generally supplies the power supply voltage and the cathode voltage meeting conditions for driving each pixel, and when the panel&#39;s temperature goes beyond a certain range, the driving current transmitted to the panel may likewise go beyond a certain range, which may result in application of excessive current. The excessive current may cause excessive brightness, which causes panel deterioration and increases the current of a switching device provided to each pixel. Also, increased current may result in degraded efficiency of the panel. 
     SUMMARY OF THE INVENTION 
     The present invention provides a power control apparatus of a display device that measures an amount of the output current of a DC power generator and adjusts that output current if it is outside a designated range. 
     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. 
     The present invention discloses a power control apparatus of a display device, comprising a first line for transmitting a first power supply voltage to a pixel, a second line for transmitting a second power supply voltage to the pixel, and a DC power generator that generates the first power supply voltage and the second power supply voltage. An output detecting unit is coupled to an output of the DC power generator, and it measures a driving current of the display device. The output detecting unit comprises an output detecting circuit for measuring the driving current and outputting a detection signal based on the measured driving current, and an output control unit for conducting a comparison of the detection signal and a designated amount of output current, and adjusting the first power supply voltage and the second power supply voltage of the DC power generator based on the comparison. 
     The present invention also discloses a method for controlling power of a display device, comprising outputting a first power supply voltage and a second power supply voltage to a pixel, measuring a driving current of the display device, and determining whether the measured driving current is within a designated range. At least one of the first power supply voltage and the second power supply voltage is adjusted when the measured driving current is not within the designated range. 
     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 embodiments of the invention and together with the description serve to explain the principles of the invention. 
         FIG. 1  is block diagram showing a conventional display device. 
         FIG. 2  is a block diagram of a power control apparatus of a display device according to an exemplary embodiment of the present invention. 
         FIG. 3  is a detailed block diagram of a power control apparatus of a display device according to an exemplary embodiment of the present invention. 
         FIG. 4  is a flow chart showing a method of controlling a display power supply according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the 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 invention to those skilled in the art. Like numbers refer to like elements throughout the specification. 
       FIG. 2  is block diagram showing a power control apparatus of a display device according to an exemplary embodiment of the present invention. 
     A data driver  100  outputs a data signal through a plurality of data lines D 1  . . . D z , a scan driver  200  outputs a selection signal through a plurality of scan lines S 1  . . . S m , a DC power generator  300  outputs a first level of power supply voltage VDD and a second level of power supply voltage VSS, and a control unit  400  controls each component. A panel  500  includes the data lines D 1  . . . D z  and the scan lines S 1  . . . S m  arranged in column and row format, and a plurality of pixels  510  are formed at intersections thereof. An output detecting unit  600  is coupled to an output of the DC power generator  300  to convert the output and to detect and control a driving current of the panel  500 . 
     Referring to  FIG. 2 , the control unit  400  is coupled to the scan driver  200 , the data driver  100 , and the DC power generator  300 , which is connected to the output detecting unit  600 . The output detecting unit  600  is coupled to the first level of power supply voltage line  520  and the second level of power supply voltage line  530 , and it is arranged close to the panel  500 . The first level of power supply voltage line  520  transmits the first level of power supply voltage VDD, and the second level of power supply voltage line  530  transmits the second level of power supply voltage VSS, to the pixels  510 . 
     The control unit  400  transmits the driving control signal to the DC power generator  300 , the scan driver  200 , and the data driver  100 . The DC power generator  300  then outputs the first level of power supply voltage VDD of +5V and the second power supply voltage VSS of −6V. Further, the scan driver  200  and the data driver  100  output the selection signal and the data signal to each pixel  510  through the scan lines S 1  . . . S m  and data lines D 1  . . . D z  according to the driving control signal. Therefore, the selection signal turns on the pixels  510 , and the data signal and the driving current by the first level of power supply voltage VDD and the second level of power supply voltage VSS are applied to each pixel  510 , so that the whole panel  500  displays an image by emitting light. 
     The output detecting unit  600  detects the driving current of the panel  500  and compares the detected driving current with a designated range. As a result, when the output detecting unit  600  detects a driving current outside the designated range, it may turn off the DC power generator  300  or control the output signal of the DC power generator  300  so that the driving current falls within the designated range. 
       FIG. 3  is a detailed block diagram illustrating a power control apparatus of a display device of an exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , the output detecting unit  600  may include an output converting means  610 , an output detecting means  620 , and a control means  630 . The output converting means  610  is coupled to the output line of the DC power generator  300 , and it adjusts the output voltage of the DC power generator  300 . The output detecting means  620 , which is coupled between the output converting means  610  and the first level of power supply voltage line  520  and the second level of power supply voltage line  530 , detects the driving current of the panel  500 . The control means  630  is coupled to the output detecting means  620 , the output converting means  610  and the DC power generator  300 , and it controls the output converting means  610  and the DC power generator  300 . 
     Here, the output voltage of the DC power generator  300  is applied to the panel  500 , which functions as a load. As a result, a driving current is generated in the panel  500  and transmitted to each pixel  510 . Therefore, it is preferable to couple the output detecting means  620  to an output of the DC power generator  300  so that the driving current may be measured close to the panel  500 . 
     An operation of the above configuration will be described with reference to the flow chart of  FIG. 4 . 
       FIG. 4  is a flow chart showing a method of controlling power of a display device according to an exemplary embodiment of the present invention. 
     As described above, when the control unit  400  applies the driving control signal, the DC power generator  300  raises or reduces a power supply voltage of approximately 2 to 3V or outputs a power supply voltage of +5V and a cathode voltage of −6V. The output voltage from the DC power generator  300  is coupled to the first level of power supply voltage line  520  and the second level of power supply voltage line  530 . (S 11 ). 
     The output detecting means  620  detects the driving current of the panel  500  applied to the first level of power supply voltage line  520  and the second level of power supply voltage line  530 , and applies the detection signal to the control means  630  (S 12 ). The output detecting means  620  may be a current sensor. 
     Therefore, the control means  630  compares the applied detection signal and the designated amount of output current. As a result, when the detection signal indicates that the driving current is not within the designated range of output current, the control means  630  outputs the voltage converting control signal to the output converting means  610  (S 13 ). 
     The output converting means  610  may then raise or reduce at least one of the first level of power supply voltage VDD and the second level of power supply voltage VSS according to the applied voltage converting control signal (S 14 ). The output converting means  610  may be a potentiometer that automatically adjusts the first level of power supply voltage VDD and the second level of power supply voltage VSS according to a relation between the designated output current and the voltage converting control signal. 
     Further, when the output converting means  610  completes the voltage conversion, the output detecting means  620  detects the converted driving current of the panel  500  so that it may apply a detection signal to the control unit  630  based on the converted driving current. The control means  630  compares this applied detection signal and the designated range to determine a result according to the voltage conversion of the output converting means  610 . In other words, after the output converting means  610  completes the voltage conversion, when the current value detected by the output detecting means  620  is within the designated range, the given voltage is applied to the first level of power supply voltage line  520  and the second level of power supply voltage line  530  (S 15 ). 
     However, if the output detecting means  620  detects an excessive current after the output converting means  610  has completed the voltage conversion, the control unit  630  determines that the output current goes beyond the adjusting range of the output converting means  610  and turns off the DC power generator  300  (S 16 ). 
     Therefore, excessive driving current may be prevented, which may prevent degradation of characteristics and efficiency of the DC power generator  300 . 
     As illustrated above, the power control apparatus according to exemplary embodiments of the present invention detects an excessive current of a panel and controls the output voltage of the DC power generator within a designated range, or turns it off, thereby preventing the degradation of efficiency and characteristics of the DC power generator. As the power supply is stably provided to the panel by the driving control of the DC power generator as described above, a switching transistor and a driving transistor provided for each pixel may be stably driven. 
     It will be apparent to those skilled in the art that various modifications and variation 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.