Patent Publication Number: US-9431903-B2

Title: DC-DC converter and organic light emitting display including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application based on pending application Ser. No. 13/586,103 filed Aug. 15, 2012, the entire contents of which is hereby incorporated by reference. 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2012-0026009, filed on Mar. 14, 2012, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments relate to a DC-DC converter and an organic light emitting display including the same. 
     2. Description of the Related Art 
     Recently, various flat panel displays (FPD) capable of reducing weight and volume that are disadvantages of cathode ray tubes (CRT) have been developed. The FPDs include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays. 
     Among the FPDs, the organic light emitting displays display images using organic light emitting diodes (OLED) that generate light by re-combination of electrons and holes. The organic light emitting display has high response speed and is driven with low power consumption. 
     SUMMARY 
     Embodiments are directed to a DC-DC converter, including a first power source generator, the first power source generator including an input port and a first output port, the first power source generator being configured to receive an input power source to the input port, and being configured to generate a first power source, the first power source being output to the first output port, and a selecting unit, the selecting unit being configured to selectively transmit, to the first power source generator, one of: a feedback voltage, the feedback voltage being input from an external feedback wiring line via a feedback terminal, and a voltage of the first output port. 
     The selecting unit may be configured to calculate a voltage difference between the feedback voltage and the voltage of the first output port, the selecting unit may be configured to select one of the feedback voltage and the voltage of the first output port to correspond to the calculated voltage difference, and the selecting unit may be configured to transmit the selected voltage to the first power source generator. 
     The selecting unit may include a calculating unit, the calculating unit being configured to calculate the voltage difference between the feedback voltage and the voltage of the first output port, and a feedback controller, the feedback controller being configured to compare the voltage difference calculated by the calculating unit with a predetermined first reference voltage, the feedback controller being configured to transmit the voltage of the first output port to the first power source generator when the voltage difference is smaller than the first reference voltage, and to transmit the feedback voltage to the first power source generator when the voltage difference is not less than the first reference voltage. 
     The feedback controller may be configured to stop driving of the first power source generator when the voltage difference is not less than a predetermined second reference voltage. 
     The second reference voltage may have a larger value than the first reference voltage. 
     The first power source generator may include a first inductor coupled between the input port and a first node, a first transistor coupled between the first node and a ground power source, a second transistor coupled between the first node and the first output port, a first switching controller, the first switching controller being configured to control the first transistor and the second transistor, and a first voltage distributing unit, the first voltage distributing unit being configured to divide a voltage supplied from the feedback controller, and being configured to supply the divided voltage to the first switching controller. 
     The first voltage distributing unit may include a plurality of serially coupled resistors. 
     Embodiments are also directed to an organic light emitting display, including a display panel including a plurality of pixels, the pixels each being coupled to a scan line, a data line, and a first power source line, and a DC-DC converter provided outside the display panel, the DC-DC converter being configured to generate a first power source and to supply the generated first power source to each of the pixels through the first power source line, the DC-DC converter including a first power source generator, the first power source generator including an input port and a first output port, the first power source generator being configured to receive an input power source to the input port, and being configured to generate a first power source, the first power source being output to the first output port, and a selecting unit, the selecting unit being configured to selectively transmit, to the first power source generator, one of a feedback voltage, the feedback voltage being input from an external feedback wiring line via a feedback terminal, and a voltage of the first output port. 
     The selecting unit may be configured to calculate a voltage difference between the feedback voltage and the voltage of the first output port, the selecting unit may be configured to select one of the feedback voltage and the voltage of the first output port to correspond to the calculated voltage difference, and the selecting unit may be configured to transmit the selected voltage to the first power source generator. 
     The selecting unit may include a calculating unit, the calculating unit being configured to calculate the voltage difference between the feedback voltage and the voltage of the first output port, and a feedback controller, the feedback controller being configured to compare the voltage difference calculated by the calculating unit with a predetermined first reference voltage, the feedback controller being configured to transmit the voltage of the first output port to the first power source generator when the voltage difference is smaller than the first reference voltage, and to transmit the feedback voltage to the first power source generator when the voltage difference is not less than the first reference voltage. 
     The feedback controller may be configured to stop driving of the first power source generator when the voltage difference is not less than a predetermined second reference voltage. 
     The second reference voltage may have a larger value than the first reference voltage. 
     The DC-DC converter may be electrically coupled to the display panel through a flexible printed circuit board (FPCB). 
     The first power source generator may include a first inductor coupled between the input port and a first node, a first transistor coupled between the first node and a ground power source, a second transistor coupled between the first node and the first output port, a first switching controller, the first switching controller being configured to control the first transistor and the second transistor, and a first voltage distributing unit, the first voltage distributing unit being configured to divide a voltage supplied from the feedback controller, and being configured to supply the divided voltage to the first switching controller. 
     The first voltage distributing unit may include a plurality of serially coupled resistors. 
     The organic light emitting display may further include a scan driver, the scan driver being configured to supply scan signals to the pixels through the scan lines, and a data driver, the data driver being configured to supply data signals to the pixels through the data lines. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages will become more apparent to those of skill in the art by describing in detail example embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a view illustrating an organic light emitting display according to an embodiment; 
         FIG. 2  is a view illustrating the detailed structure of the organic light emitting display of  FIG. 1 ; 
         FIG. 3  is a view illustrating an embodiment of the pixel of  FIG. 2 ; 
         FIG. 4  is a view illustrating a DC-DC converter according to the embodiment; 
         FIG. 5  is a view illustrating the detailed structure of the DC-DC converter of  FIG. 4 ; and 
         FIG. 6  is a view additionally illustrating a feedback wiring line in the organic light emitting display of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings; however, they may 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. 
     Hereinafter, a DC-DC converter and an organic light emitting display including the same will be described. 
       FIG. 1  is a view illustrating an organic light emitting display according to an embodiment.  FIG. 2  is a view illustrating the detailed structure of the organic light emitting display of  FIG. 1 . 
     Referring to  FIG. 1 , the organic light emitting display according to an example embodiment includes a display panel  10  and a DC-DC converter  20 . 
     In the present example embodiment, the display panel  10  includes a plurality of pixels  12  to display a predetermined image. 
     In the present example embodiment, the DC-DC converter  20  is positioned outside the display panel  10  to generate power sources required for the display panel  10  and to supply the generated power sources. 
     The DC-DC converter  20  may be electrically coupled to the display panel  10  through a flexible printed circuit board (FPCB)  40  while being mounted on a printed circuit board (PCB)  30 . In another implementation, the DC-DC converter  20  may be directly mounted on the FPCB  40  and may be electrically coupled to the display panel  10  through a PCB that does not have flexibility. 
     The DC-DC converter  20  may not be directly mounted on the display panel  10 , but instead may be positioned outside the display panel  10  to be electrically coupled to the display panel  10  through the PCBs  30  and  40 . Thus, the voltage of the power source output from the DC-DC converter  20  may be reduced while passing through the PCBs  30  and  40 . 
     Referring to  FIG. 2 , the detailed structure of the organic light emitting display according to the embodiment will be described. 
     In the present example embodiment, the organic light emitting display includes a display panel  10  including a plurality of pixels  12  coupled to scan lines S 1  to Sn, data lines D 1  to Dm, a first power source line  181 , and a second power source line  182 , a scan driver  130  for supplying scan signals to the pixels  12  through the scan lines S 1  to Sn, a data driver  140  for supplying data signals to the pixels  12  through the data lines D 1  to Dm, a timing controller  150  for controlling the scan driver  130  and the data driver  140 , and the DC-DC converter  20  for supplying a first power source ELVDD and a second power source ELVSS to the pixels  12  through the first power source line  181  and the second power source line  182 . 
     In the present example embodiment, the pixels  12  that receive the first power source 
     ELVDD and the second power source ELVSS from the DC-DC converter  20  through the first power source line  181  and the second power source line  182  generate light components corresponding to the data signals by the current that flows from the first power source ELVDD to the second power source ELVSS via organic light emitting diodes (OLED). 
     The scan driver  130  generates the scan signals by the control of the timing controller  150  and supplies the generated scan signals to the scan lines S 1  to Sn. 
     The data driver  140  generates the data signals by the control of the timing controller  150  and supplies the generated data signals to the data lines D 1  to Dm. 
     When the scan signals are sequentially supplied to the scan lines S 1  to Sn, the pixels  12  are sequentially selected by lines and the selected pixels  12  receive the data signals transmitted from the data lines D 1  to Dm. 
     When the scan driver  130 , the data driver  140 , and the timing controller  150  are provided in the display panel  10 , the scan driver  130 , the data driver  140 , and the timing controller  150  may be referred to as a display module  100 . 
       FIG. 3  is a view illustrating an embodiment of the pixel of  FIG. 2 . In  FIG. 3 , for convenience sake, the pixel coupled to the nth scan line Sn and the mth data line Dm are illustrated. 
     In the present example embodiment, each of the pixels  12  includes a pixel circuit  15  (coupled to the OLED, the data line Dm, and the scan line Sn) to control the OLED. 
     In the present example embodiment, the anode electrode of the OLED is coupled to the pixel circuit  15  and the cathode electrode of the OLED is coupled to the second power source ELVSS. 
     In the present example embodiment, the OLED generates light of predetermined brightness to correspond to the current supplied from the pixel circuit  15 . The pixel circuit  15  controls the amount of current supplied to the OLED to correspond to the data signal supplied to the data line Dm when the scan signal is supplied to the scan line Sn. 
     In the present example embodiment, the pixel circuit  15  includes a second transistor T 2  coupled between the first power source ELVDD and the OLED, a first transistor T 1  coupled among the second transistor T 2 , the data line Dm, and the scan line Sn, and a storage capacitor Cst coupled between the gate electrode of the second transistor T 2  and the first electrode of the second transistor T 2 . 
     The gate electrode of the first transistor T 1  is coupled to the scan line Sn and the first electrode of the first transistor T 1  is coupled to the data line Dm. 
     The second electrode of the first transistor T 1  is coupled to one terminal of the storage capacitor Cst. 
     The first electrode is set as one of a source electrode and a drain electrode, and the second electrode is set as an electrode different from the first electrode. For example, when the first electrode is set as the source electrode, the second electrode is set as the drain electrode. 
     The first transistor T 1  (coupled to the scan line Sn and the data line Dm) is turned on when the scan signal is supplied from the scan line Sn, so as to supply the data signal supplied from the data line Dm to the storage capacitor Cst. At this time, the storage capacitor Cst charges the voltage corresponding to the data signal. 
     The gate electrode of the second transistor T 2  is coupled to one terminal of the storage capacitor Cst, and the first electrode of the second transistor T 2  is coupled to the other terminal of the storage capacitor Cst and the first power source ELVDD. The second electrode of the second transistor T 2  is coupled to the anode electrode of the OLED. 
     The second transistor T 2  controls the amount of current that flows from the first power source ELVDD to the second power source ELVSS via the OLED to correspond to the voltage value stored in the storage capacitor Cst. At this time, the OLED generates the light corresponding to the amount of current supplied from the second transistor T 2 . 
     The above-described structure of the pixel of  FIG. 3  is only an example embodiment, and the pixel circuit  15  may have various circuit structures for supplying current to the OLED. 
     In the present example embodiment, the DC-DC converter  20  receives an input power source Vin from the power source unit  50  to convert the input power source Vin, and to generate the first power source ELVDD and the second power source ELVSS supplied to the pixels  12 . 
     As described above, the DC-DC converter  20  may be electrically coupled to the first power source line  181  and the second power source line  182  that exist in the display panel  10  by the FPCB  40 . The DC-DC converter  20  may supply the first power source ELVDD and the second power source ELVSS to the pixels  12  through the first power source line  181  and the second power source line  182 . 
     The first power source ELVDD is preferably set as a positive polarity voltage and the second power source ELVSS is preferably set as a negative polarity voltage. 
     The power source unit  50  may be, e.g., a battery for providing a direct current (DC) power source to the input port IN of the DC-DC converter  20 , a rectifying apparatus for converting an alternating current (AC) power source into the DC power source to output the DC power source, etc. 
       FIG. 4  is a view illustrating a DC-DC converter according to the embodiment.  FIG. 5  is a view illustrating the detailed structure of the DC-DC converter of  FIG. 4 . 
     Referring to  FIG. 4 , the DC-DC converter  20  according to the present example embodiment may include a first power source generator  210 , a second power source generator  220 , and a selecting unit  230 . 
     In the present example embodiment, the first power source generator  210  receives the input power source Vin supplied from the power source unit  50  to the input port IN to generate the first power source ELVDD, and outputs the first power source ELVDD to a first output port OUT 1 . The first power source ELVDD may be supplied to the pixels  12  through the first power source line  181  electrically coupled to the first output port OUT I. 
     In the present example embodiment, the first power source generator  210  increases the voltage of the input power source Vin using internal elements to generate the first power source ELVDD. In addition, the first power source generator  210 , as a boost type converter that increases the voltage of the input power source Vin, may generate the first power source ELVDD having a positive polarity voltage. 
     In an example embodiment, referring to  FIG. 5 , the first power source generator  210  may include a first inductor L 1 , a first transistor M 1 , a second transistor M 2 , a first switching controller  310 , and a first voltage distributing unit  320 . 
     The first inductor L 1  is coupled between the input port IN and a first node N 1 . 
     The first transistor M 1  is coupled between the first node N 1  and a ground power source. 
     The second transistor M 2  is coupled between the first node N 1  and the first output port OUT 1 . 
     The first switching controller  310  controls the first transistor M 1  and the second transistor M 2 . In addition, the first switching controller  310  controls the on and off operations of the first transistor M 1  and the second transistor M 2  to convert the input power source Vin into the first power source ELVDD having a desired voltage level. 
     The first voltage distributing unit  320  divides a voltage supplied from the selecting unit  230  (the voltage Vout 1  of the first output port OUT 1  or a feedback voltage Vfbp) to supply the divided voltage to the first switching controller  310 . 
     The first voltage distributing unit  320  may include a plurality of serially coupled resistors (for example, R 1  and R 2 ). 
     The first switching controller  310  that receives the voltage divided by the first voltage distributing unit  320  controls the duty ratios of the first transistor M 1  and the second transistor M 2  to correspond to the divided voltage to generate a desired first power source ELVDD. 
     The first transistor M 1  and the second transistor M 2  may be alternately turned on, and may have different conductivity types. For example, when the first transistor M 1  is a P type, the second transistor M 2  may be an N type. 
     The structure of the above-described first power source generator  210  is merely an example, and embodiments are not limited to the above. 
     In the present example embodiment, the second power source generator  220  receives the input power source Vin supplied from the power source unit  50  to the input port IN to generate the second power source ELVSS, and outputs the second power source ELVSS to a second output port OUT 2 . The second power source ELVSS may be supplied to the pixels  12  through the second power source line  182  electrically coupled to the second output port OUT 2 . 
     The second power source generator  220  converts the voltage of the input power source 
     Vin using internal elements to generate the second power source ELVSS. 
     In addition, the second power source generator  220 , as a buck type converter for reducing the voltage of the input power source Vin, preferably generates the second power source ELVSS having a negative polarity voltage. 
     In an example embodiment, referring to  FIG. 5 , the second power source generator  220  may include a second inductor L 2 , a third transistor M 3 , a fourth transistor M 4 , a second switching controller  330 , and a second voltage distributing unit  340 . 
     The third transistor M 3  is coupled between the input end IN and a second node N 2 . 
     The fourth transistor M 4  is coupled between the second node N 2  and the second output port OUT 2 . 
     The second inductor L 2  is coupled between the second node N 2  and a ground power source. 
     The second switching controller  330  controls the third transistor M 3  and the fourth transistor M 4 . In addition, the second switching controller  330  controls the on and off operations of the third transistor M 3  and the fourth transistor M 4  to convert the input power source Vin into the second power source ELVSS having a desired voltage level. 
     The second voltage distributing unit  340  divides the voltage Vout 2  transmitted from the second output port OUT 2  to supply the divided voltage to the second switching controller  330 . 
     The second voltage distributing unit  340  may include a plurality of serially coupled resistors (for example, R 3  and R 4 ). 
     The second switching controller  330  that receives the voltage divided by the second voltage distributing unit  340  controls the duty ratios of the third transistor M 3  and the fourth transistor M 4  to correspond to the divided voltage to generate the desired second power source ELVSS. 
     The third transistor M 3  and the fourth transistor M 4  may be alternately turned on and may have different conductivity types. For example, when the third transistor M 3  is the N type, the fourth transistor M 4  may be the P type. 
     The above-described structure of the second power source generator  220  is only an example, and embodiments are not limited to the above. 
     The selecting unit  230  may selectively transmit, to the first power source generator  210 , one of: the feedback voltage Vfbp input to the feedback terminal FBP of the DC-DC converter  20 , and the voltage Vout 1  of the first output port OUT 1 . 
     The first power source generator  210  may properly control the voltage level of the output first power source ELVDD by reflecting the voltage (the feedback voltage Vfbp) fed-back by the selecting unit  230  or the voltage Vout 1  of the first output port OUT 1 . 
     In an example embodiment, referring to  FIG. 6 , a feedback wiring line  190  as a wiring line for electrically coupling the first power source line  181  and the feedback terminal FBP that exist in the display panel  10  may input the voltage of the first power source line  181  to the feedback terminal FBP. In addition, the feedback wiring line  190  may be extended through at least one circuit board  30  and  40  in order to electrically couple the first power source line  181  and the feedback terminal FBP to each other. 
     A predetermined voltage difference exists between the voltage Vout 1  of the first output port OUT 1  of the DC-DC converter  20  and the voltage of the first power source line  181  in the display panel  10  coupled to the pixels  12 . In order to correctly control the first power source generator  210 , the feedback voltage used by the display panel  10  may be used as the feedback voltage, instead of the voltage Vout 1  of the first output port OUT 1 . Therefore, the feedback wiring line  190  and the selecting unit  230  electrically coupled to the first power source line  181  that exists in the display panel  10  may be provided so that one of the voltage Vout 1  of the first output port OUT 1  and the feedback voltage Vfbp may be selectively supplied to the first power source generator  210 . 
     In the present example embodiment, the selecting unit  230  receives the feedback voltage Vfbp and the voltage Vout 1  of the first output port OUT 1  to calculate a voltage difference between the two voltages, and selects the voltage to be transmitted to the first power source generator  210  from the two voltages to correspond to the calculated voltage difference. 
     The selecting unit  230  according to the present example embodiment may include a calculating unit  231  for performing the above-described function and a feedback controller  232 . 
     The calculating unit  231  receives the feedback voltage Vfbp and the voltage Vout 1  of the first output port OUT 1  to calculate a voltage difference ΔV between the two voltages and transmits the calculated voltage difference ΔV to the feedback controller  232 . 
     The feedback controller  232  selects a voltage to be transmitted to the first power source generator  210  from the feedback voltage Vfbp and the voltage Vout 1  of the first output port OUT 1  with reference to the voltage difference ΔV transmitted from the calculating unit  231 . For example, the feedback controller  232  compares a predetermined first reference voltage Vref 1  with the voltage difference ΔV calculated by the calculating unit  231 , to transmit the voltage Vout 1  of the first output port OUT 1  to the first power source generator  210  when the voltage difference ΔV is smaller than the first reference voltage Vref 1 , and to transmit the feedback voltage Vfbp to the first power source generator  210  when the voltage difference ΔV is no less than the first reference voltage Vref 1 . 
     When the difference between the voltage Vout 1  of the first output port OUT 1  and the feedback voltage Vfbp is small, the voltage Vout 1  of the first output port OUT 1  may be fed-back to the first power source generator  210 . When the difference between the voltage Vout 1  of the first output port OUT 1  and the feedback voltage Vfbp is large, the feedback voltage Vfbp is fed-back to the first power source generator  210 . Therefore, the first power source generator  210  may be effectively controlled. 
     At this time, the feedback controller  232  may stop the driving of the first power source generator  210  when the voltage difference ΔV calculated by the calculating unit  231  is no less than a predetermined second reference voltage Vref 2 . When the first power source line  181  that exists in the display panel  10  is broken or shorted from another wiring line, the voltage difference ΔV between the feedback voltage Vfbp and the voltage Vout 1  of the first output port OUT 1  may become significantly large. Therefore, when the voltage difference ΔV is no less than the second reference voltage Vref 2 , the driving of the first power source generator  210  is stopped to prevent additional damage from being caused as a result of the first power source line  181  being broken or shorted. Therefore, when the voltage difference ΔV is no less than the second reference voltage Vref 2 , the feedback controller  232  may supply a driving stop signal Pst to the first switching controller  310  of the first power source generator  210 . 
     The first switching controller  310  that receives the driving stop signal Pst turns off all of the transistors (for example, M 1  and M 2 ) included in the first power source generator  210  to stop the driving of the first power source generator  210 . 
     In addition, the feedback controller  232  may supply the driving stop signal Pst to the second switching controller  330  of the second power source generator  220  when the voltage difference ΔV is no less than the second reference voltage Vref 2 . The second switching controller  330  that receives the driving stop signal Pst turns off all of the transistors (for example, M 3  and M 4 ) included in the second power source generator  220  to stop the driving of the second power source generator  220 . 
     The first reference voltage Vref 1  and the second reference voltage Vref 2  may be variously set. The second reference voltage Vref 2  is preferably set to have a larger value than the first reference voltage Vref 1 . 
     By way of summation and review, an organic light emitting display may include a display panel, including a plurality of pixels to display an image, and a DC-DC converter for supplying a power source from the outside of the display panel to the display panel through a flexible printed circuit board (FPCB). 
     The DC-DC converter may convert an external power source to generate power sources required for driving the display panel. A power source output to an output port may be fed back to the DC-DC converter in order to control the voltage of the output power source. A voltage drop may be generated by a FPCB that exists between the display panel and the DC-DC converter. Thus, a voltage of the power source input to the display panel may be lower than the output voltage of the DC-DC converter. Where a voltage higher than the voltage of the power source used for the display panel is fed back to a general DC-DC converter, a power source having a lower voltage than required for the display panel may be output. Therefore, the brightness of the display panel may be lower than a target brightness. 
     As described above, embodiments relate to a DC-DC converter capable of feeding back the voltage of the power source in a display panel to prevent brightness from deteriorating and an organic light emitting display including the same. An embodiment may provide a DC-DC converter capable of selectively feeding back a voltage of the output port of the DC-DC converter and a voltage of the power source in a display panel, so as to correctly control the voltage of an output power source and to prevent the brightness of the display panel from deteriorating. An embodiment also provides an organic light emitting display including the DC-DC converter. 
     Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of ordinary skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.