Abstract:
A display device comprising a display panel, a first voltage supply unit, a second voltage supply unit, and a detecting unit. The first voltage supply unit supplies a first voltage to the display panel. The second voltage supply unit supplies a second voltage to the display panel according to a control signal. The detecting unit detects the first voltage. The detecting unit generates the control signal when detecting the variance in the first voltage.

Description:
BACKGROUND  
       [0001]     The invention relates to a power device, and in particular to a power device applied in a display device.  
         [0002]      FIG. 1  is a schematic diagram of a panel of a conventional organic light emitting display (OLED) device. A panel  1  comprises a data driver  10 , a scan driver  11 , and a display array  12 . The data driver  10  controls a plurality of data lines D 1  to D n , and the scan driver  11  controls a plurality of scan lines S 1  to S m . The display array  12  is formed by the interlaced data lines D 1  to D n  and scan lines S 1  to S m . Each interlaced data line and scan line control a display unit of the display array  12 . For example, the data line D 1  and the scan line S 1  control a display unit  100 . As with any other display unit, the equivalent circuit of the display unit  100  comprises a switch transistor T 10 , a storage capacitor C 10 , a driving transistor T 11 , and a light-emitting diode (LED) D 10 .  
         [0003]     An OLED device is a self-illuminating flat panel display. Light from the LED D 10  is transformed from current I flowed itself. The brightness of the LED D 10  can be determined according to the current I provided by the driving transistor T 11 . In the panel  1 , voltage Vdd, provided to the driving transistor T 11 , must be adjusted due to process derivation of the driving transistor T 11 , thus, the brightness from all the display units of the display array  12  reaches a predetermined level. In general, the adjustment range of the voltage Vdd is 2V.  
         [0004]     Referring to  FIG. 2 , an external power device provides the voltage Vdd and Vss to each display unit. The external power device provides the power consumed by all LEDs of the display array  12 . In the display array  12 , nodes of the voltage Vdd are connected, and nodes of the voltage Vss are connected. The nodes of the voltage Vdd and Vss are led to outer edges of the panel  1  and connected to the external power device  2  through leads.  
         [0005]     Conventional external power devices adjust voltage Vdd and Vss or voltage Vdd only.  FIG. 3   a  shows a conventional external power device adjusting voltage Vdd. An external power device  2  comprises DC/DC converters  31  and  32  and adjusting devices  33  and  34 . The DC/DC converters  31  and  32  respectively provide voltage Vdd and Vss. Both adjusting devices  33  and  34  have two impedance elements R. A value of an impedance element R 1  of the adjusting devices  33  is adjustable, and a value of an impedance element R 2  thereof is fixed. When the DC/DC converter  31  provides the voltage Vdd to the panel  1 , a feedback voltage Vf 1  is acquired by dividing the voltage Vdd by the impedance elements R 1  and R 2 . The DC/DC converter  31  determines the value of the voltage Vdd according to the feedback voltage Vf 1 . When the voltage Vdd requires adjustment due to the process derivation of the transistor T 11 , the feedback voltage Vf 1  is varied by adjusting the value of the impedance elements R 1 . The DC/DC converters  31  thus adjust the value of the voltage Vdd according to the varied feedback voltage Vf 1 . Since the DC/DC converter  32  provides the fixed voltage Vss, the values of the impedance elements R 3  and R 4  are fixed. For a panel only requiring 10V cross-voltage, which is defined by the voltage between Vdd and Vss, the cross-voltage of the entire panel varies between 10V and 12V, resulting in a maximum consumption increment of 20% power for the panel.  
         [0006]      FIG. 3   b  shows a conventional external power device adjusting both voltage Vdd and Vss. An external power device  3  comprises DC/DC converters  35  and  36  and adjusting devices  37  and  38 . The DC/DC converters  35  and  36  respectively provide voltage Vdd and Vss. Both adjusting devices  37  and  38  have two impedance elements R. A value of an impedance element R 5  of the adjusting devices  37  is adjustable, and a value of an impedance element R 6  thereof is fixed. When the voltage Vdd needs to be adjusted due to process derivation of the transistor T 11 , the feedback voltage Vf 1  is varied by adjusting the value of the impedance elements R 5 , and the DC/DC converters  35  thus adjusts the value of the voltage Vdd according to the varied feedback voltage Vf 1 . After the voltage Vdd is adjusted, the voltage Vss is adjusted to avoid the excess power consumption, so that the cross-voltage between Vdd and Vss is maintained at 10V. In the external power device  3 , a value of an impedance element R 7  of the adjusting devices  38  is adjustable, and a value of an impedance element R 8  thereof is fixed. The DC/DC converter  36  and adjusting devices  38  perform the same operation respectively as the DC/DC converter  35  and adjusting devices  37 . When the voltage Vss needs to be adjusted due to the process derivation, the feedback voltage Vf 2  is varied by adjusting the value of the impedance elements R 7 , and the DC/DC converters  36  thus adjusts the value of the voltage Vss according to the varied feedback voltage Vf 2 . According to the external power device of  FIG. 3   b,  when process derivation of the transistor T 11  occurs, not only the voltage Vdd but also the voltage Vss is adjusted, resulting in an increased number of manufacturing processes for OLED devices.  
       SUMMARY  
       [0007]     An exemplary embodiment of a display device comprises a display panel, a first voltage supply unit, a second voltage supply unit, and a detecting unit. The first voltage supply unit provides first voltage to the display panel. The second voltage supply unit provides second voltage to the display panel according to a control signal. The detecting unit detects the first voltage. The detecting unit generates the control signal upon detecting variance in the first voltage.  
         [0008]     In some embodiments, when the first voltage increases, the second voltage increases. The variation of the first voltage is equal to the variation of the second voltage.  
         [0009]     An exemplary embodiment of a display device comprises a display panel, a first voltage supply unit, a second voltage supply unit, and a detecting unit. The first voltage supply unit supplies a first voltage to the display panel. The second voltage supply unit supplies a second voltage to the display panel according to a control signal. The detecting unit detects the first and second voltage and calculates cross-voltage between the first and second voltage. When the cross-voltage is not equal to a reference voltage, the detecting unit generates the control signal. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]     The invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, given by way of illustration only and thus not intended to be limitative of the invention.  
         [0011]      FIG. 1  shows a panel of a conventional OLED device.  
         [0012]      FIG. 2  shows a block diagram of a panel and an external power device of a conventional OLED device.  
         [0013]      FIGS. 3   a  and  3   b  show conventional external power devices.  
         [0014]      FIG. 4  shows an embodiment of a display device.  
         [0015]      FIG. 5  shows an embodiment of a display device. 
     
    
     DETAILED DESCRIPTION  
       [0016]     In an exemplary embodiment of a display device shown in  FIG. 4 , a display device  4  comprises a display panel  40  and a power device  41 . In this embodiment, the display panel  40  comprises the same display array as the panel  1  in  FIG. 1 . Each display unit of the display array requires voltage Vdd and Vss, and the cross-voltage between the voltage Vdd and Vss is 10V. The power device  41  comprises voltage supply units  410  and  411  respectively providing the voltage Vdd and Vss to the display panel  40 . In this embodiment, the voltage supply units  410  and  411  can be DC/DC converter, the value of the voltage Vdd is positive, and the value of the voltage Vss is negative. The power device  41  further comprises a detecting unit  412  and an adjusting unit  413 . The adjusting unit  413  detects the voltage Vdd and outputs a corresponding adjusting signal S 1  to the voltage supply unit  410 , so that the voltage supply unit  410  continuously provides the same voltage Vdd according to the adjusting signal S 1 . When the voltage Vdd needs to be adjusted due to the process derivation of the driving transistor, the adjusting unit  413  varies the adjusting signal S 1 . The voltage supply unit  410  adjusts the value of the voltage Vdd according to the varied feedback voltage S 1 . In other words, when the adjusting signal S 1  is varied, the voltage supply unit  410  varies the value of the voltage Vdd.  
         [0017]     The detecting unit  412  also detects the voltage Vdd. When detecting the variance in the voltage Vdd, the detecting unit  412  generates a corresponding control signal S 2 . The voltage supply unit  411  determines the value of the voltage Vss according to the control signal S 2 , so that the cross-voltage between the voltage Vdd and Vss maintains at 10V. The voltage Vss increases as the voltage Vdd increases, and the voltage Vss decreases as the voltage Vdd decreases. In other words, the variation of the voltage Vdd is equal to that of the voltage Vss.  
         [0018]     According to the embodiment of  FIG. 4 , when the value of the voltage vDD is varied, the detecting unit  412  simultaneously provides the control signal S 2  to the voltage supply unit  411  to vary the value of the voltage Vss automatically. The cross-voltage between the voltage Vdd and Vdd does not vary when the voltage is adjusted, avoiding the increment in consumed power.  
         [0019]     In an exemplary embodiment of a display device in  FIG. 5 , a display device  5  comprises a display panel  50  and a power device  51 . In this embodiment, the display panel  50  comprises the same display array as the panel  1  in  FIG. 1 . Each display unit of the display array requires voltage Vdd and Vss, and the cross-voltage between the voltage Vdd and Vss is 10V. The power device  51  comprises voltage supply units  510  and  511  respectively providing the voltage Vdd and Vss to the display panel  50 . In this embodiment, the voltage supply units  510  and  511  can be DC/DC converters, the value of the voltage Vdd is positive, and the value of the voltage Vss is negative. The power device  51  further comprises a detecting unit  512  and an adjusting unit  513 . The adjusting unit  513  detects the voltage Vdd and outputs a corresponding adjusting signal S 3  to the voltage supply unit  510 , so that the voltage supply unit  510  continuously provides the same voltage Vdd according to the adjusting signal S 3 . When the voltage Vdd requires adjustment due to process derivation of the driving transistor, the adjusting unit  513  varies the adjusting signal S 3 . The voltage supply unit  510  adjusts the value of the voltage Vdd according to the varied feedback voltage S 3 . In other words, when the adjusting signal S 3  is varied, the voltage supply unit  510  varies the value of the voltage Vdd.  
         [0020]     The detecting unit  512  detects not only the voltage Vdd but also the voltage Vss. The detecting unit  512  has a reference cross-voltage, and in this embodiment, the reference cross-voltage is equal to 10V. The detecting unit  512  detects the voltage Vdd and Vss and calculates the cross-voltage between voltage Vdd and Vss. When the voltage Vdd is adjusted, the calculated cross-voltage is not equal to 10V, and the detecting unit  512  generates a corresponding control signal S 4 . The voltage supply unit  511  determines the value of the voltage Vss according to the control signal S 4 , so that the cross-voltage between the voltage Vdd and Vss maintains at 10V.  
         [0021]     According to the embodiment of  FIG. 5 , when the cross-voltage between the voltage Vdd and Vdd is varied due to the adjusted voltage Vdd, the detecting unit  512  simultaneously provides the control signal S 4  to the voltage supply unit  511  to automatically vary the value of the voltage Vss. The cross-voltage between the voltage Vdd and Vdd does not vary when the voltage Vdd is adjusted, avoiding the increment in consumed power.  
         [0022]     While the invention has been described in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.