Patent Publication Number: US-8994624-B2

Title: Power supplying apparatus, power supplying method, organic light-emitting diode display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 from Korean Patent Application Nos. 10-2011-145313, filed on Dec. 28, 2011; 10-2011-147497, filed on Dec. 30, 2012; and 10-2012-0042798, filed on Apr. 24, 2012, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     1. Field 
     Apparatuses and methods consistent with exemplary embodiments relate to a power supplying apparatus, a power supplying method, an organic light-emitting diode (OLED) display apparatus, and more particularly, to a display apparatus including an OLED and a method of supplying power thereto. 
     2. Description of the Related Art 
     The development of electronic technology has brought the development and supply of various types of electronic products. In particular, various types of display apparatuses, such as a TV, a portable phone, a personal computer (PC), a notebook PC, a personal digital assistant (PDA), etc., are used in most general homes. 
     A conventional display apparatus displays various types of images by using a liquid crystal display (LCD). The conventional LCD is not a self-emission display apparatus and thus uses a backlight unit as a light source. 
     In general, a display apparatus rectifies a commercial voltage of 110 V or 220 V applied from an external source and supplies the rectified commercial voltage to power consumption parts of the display apparatus. Since a backlight unit requires a driving voltage higher than the other power consumption parts, the display apparatus is to separately include a main DC-DC converter which is to supply power to the backlight unit and a sub DC-DC converter which is to supply power to the other parts. 
     Therefore, a conventional LCD requires additional cost, and the display apparatus is limitedly made slim and light. Also, the conventional LCD requires backlight and thus is heavy and thick and has a slow response speed. 
     An organic light-emitting display has been developed as a next generation image display apparatus replacing an LCD. The organic light-emitting display displays an image by using organic light-emitting diodes (OLEDs) which emit light through a recombination of electrons and holes. 
     Here, each of the OLEDs of the organic light-emitting display includes an anode, a cathode, and an emission layer formed between the anode and the cathode. Also, if a current flows from the anode to the cathode, the emission layer emits light, and an amount of the light varies according to changes of an amount of the current, thereby representing luminance. 
     The organic light-emitting display using the above-described OLEDs has a high color representation and a thin thickness. Therefore, the organic light-emitting display has wide application in a portable phone, a PDA, an MP3 player, etc. 
     A method of driving the organic light-emitting display using the OLEDs is greatly classified into a passive matrix method and an active matrix method. The passive matrix method refers to a method of orthogonally forming an anode and a cathode and applying a current to selected cathode and anode lines to drive the anode and the cathode. The active matrix method refers to a method of integrating a thin film transistor (TFT) and a capacitor into each pixel to maintain a voltage due to a capacitance of the capacitor. 
     A process of driving an organic light-emitting display including general OLED pixels by using an active matrix method will now be described with reference to  FIG. 1 . 
       FIG. 1  is a circuit diagram illustrating a process of driving a conventional organic light-emitting display by using an active matrix method. 
     Referring to  FIG. 1 , the conventional organic light-emitting display includes OLEDs each including scan lines SL and data lines DL which cross each other, a switching transistor T 1 , a driving transistor T 2 , and a capacitor C. The switching transistor T 1  includes a gate which is connected to the scan lines SL and a source which is connected to the data lines DL. The driving transistor T 2  includes a gate which is connected to a drain of the switching transistor T 1  and a source which is connected to a first power source ELVDD. The capacitor C is formed between the source and the gate of the driving transistor T 2 . A drain and an anode of the driving transistor T 2  are connected to each other, and the source is connected to a second power source ELVSS. 
     A circuit operation of the organic light-emitting display will now be described. If the switching transistor T is turned on, a data voltage is applied to a gate electrode of the driving transistor T 2 . Also, a current flows in the OLED through the driving transistor T 2  due to the data voltage to emit and display light. In addition, the data voltage applied to the gate electrode is maintained for a predetermined time due to the capacitor C. 
     An OLED as described above has low voltage and high current characteristics. Therefore, if a conventional power supply unit (e.g., a switch mode power supply (SMPS)) is applied, high power efficiency is not achieved. 
     SUMMARY 
     Exemplary embodiments address at least the above problems and/or disadvantages and other disadvantages not described above. Also, the exemplary embodiments are not required to overcome the disadvantages described above, and an exemplary embodiment may not overcome any of the problems described above. 
     The exemplary embodiments provide a display apparatus which applies a voltage having the same level to a display panel having an organic light-emitting diode (OLED) and other power consumption parts and a method of supplying power thereto. 
     The exemplary embodiments also provide a power supplying apparatus which controls turning on/off of a power factor correction (PFC) unit in a data voltage charging section and a light emitting section to improve power efficiency, a power supplying method, and a display apparatus. 
     According to an aspect of exemplary embodiments, there is provided an organic light-emitting diode (OLED) display apparatus including: a plurality of components which are to perform an operation of the OLED display apparatus; a power supplier; a rectifier which rectifies an input voltage supplied from the power supplying unit; and a voltage level converter which converts a level of the input voltage rectified by the rectifier and supplies the input voltage having the converted level to the plurality of components. 
     The rectifier may include a power factor correction (PFC) unit which corrects a power factor of the input voltage. 
     The voltage level converter may convert a level of a direct current (DC) voltage output from the PFC unit into a voltage level for driving a display panel and may supply the DC voltage having the voltage level to the plurality of components. 
     The display panel may include a plurality of pixels including OLEDs. 
     The OLED display apparatus may further include a controller which controls the PFC unit to be turned on/off according to operation states of the plurality of components. 
     The controller may turn off the PFC unit when the display panel performs a data voltage charging operation and turn on the PFC unit when the display panel performs a light emitting operation. 
     The controller may detect a level of the DC voltage supplied to the display panel, and if the detected level of the DC voltage is a first voltage level, determine that the display panel performs the data voltage charging operation to turn off the PFC unit, and if the detected level of the DC voltage is a second voltage level, determine that the display panel performs the light emitting operation to turn on the PFC unit. 
     The controller may turn on the PFC unit before a preset time based on a time when a data voltage charging operation ends. 
     If an output voltage of the PFC unit is lower than or equal to a preset level when the PFC unit is turned off, the controller may determine that the preset time has elapsed and turn on the PFC unit. 
     The OLED display apparatus may further include: a scan driver which supplies a scan signal to the plurality of pixels; a data driver which supplies a data signal to the plurality of pixels; and a voltage driver which supplies a driving voltage to the display panel. 
     The plurality of components may include at least one from among a display panel, an audio amplifier, a communication interface module, and a sub Micom. 
     According to another aspect of exemplary embodiments, there is provided a power supplying apparatus which supplies power to a display panel comprising a plurality of pixels comprising OLEDs. The power supplying apparatus may include: a power factor correction (PFC) unit which corrects a power factor of an input voltage; a DC-DC converter which converts a level of a DC voltage output from the PFC unit and supplies the DC voltage having the converted level to the display panel; and a controller which controls the PFC unit to be turned on/off according to an operation state of the display panel. 
     The controller may turn off the PFC unit when the display panel performs a data voltage charging operation but turn on the PFC unit when the display panel performs a light emitting operation. 
     The controller may detect a level of the DC voltage supplied to the display panel, and if the detected level of the DC voltage is a first voltage level, determines that the display panel performs the data voltage charging operation to turn off the PFC unit, and if the detected level of the DC voltage is a second voltage level, determine that the display panel performs the light emitting operation to turn on the PFC unit. 
     The controller may turn on the PFC unit before a preset time based on a time when a data voltage charging operation ends. 
     If an output voltage of the PFC unit is lower than or equal to a preset level when the PFC unit is turned off, the controller may determine that the preset time has elapsed and turn on the PFC unit. 
     According to another aspect of the exemplary embodiments, there is provided a method of supplying power to a display panel comprising a plurality of pixels comprising OLEDs. The method may include: correcting a power factor of an input voltage by using a power factor correction (PFC) unit; converting a level of a DC voltage output through the correction and supplying the DC voltage having the converted level to the display panel; and turning on/off the PFC unit according to an operation state of the display panel. 
     The turning on/off of the PFC unit may include: turning off the PFC unit when the display panel performs a data voltage charging operation; and turning on the PFC unit when the display panel performs a light emitting operation. 
     The turning on/off of the PFC unit may further include: detecting a level of the direct current (DC) voltage supplied to the display panel, wherein if the detected level of the DC voltage is a first voltage level, a determination is made that the display panel performs the data voltage charging operation to turn off the PFC unit, and if the detected level of the DC voltage is a second voltage level, a determination is made that the display panel performs the light emitting operation to turn on the PFC unit. 
     The PFC unit may be turned on before a preset time based on a time when a data voltage charging operation ends. 
     If an output voltage of the PFC unit is lower than or equal to a preset level when the PFC unit is turned off, a determination may be made that the output voltage. 
     According to various exemplary embodiments, a voltage having the same level may be applied to a display panel including OLEDs and other power consumption parts by using one DC-DC converter in order to drive modules of a display apparatus. Also, a PFC unit may be controlled to be turned on/off in a data voltage charging section and a light-emitting section to improve power efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects will be more apparent by describing certain exemplary embodiments with reference to the accompanying drawings, in which: 
         FIG. 1  is a circuit diagram illustrating a process of driving a conventional organic light-emitting display by using an active matrix method; 
         FIG. 2  is a block diagram of an organic light-emitting diode (OLED) display apparatus according to an exemplary embodiment; 
         FIG. 3  is a timing diagram illustrating an operation characteristic of a power factor correction (PFC) unit according to an exemplary embodiment of; 
         FIG. 4  is a block diagram illustrating a detailed structure of a display apparatus according to an exemplary embodiment; 
         FIG. 5  is a circuit diagram of RGB pixels of a display panel according to an exemplary embodiment; 
         FIG. 6  is a block diagram of a power supplying apparatus which supplies power to a display panel including a plurality of RGB pixels having organic light-emitting diodes (OLEDs), according to an exemplary embodiment; 
         FIG. 7  is a flowchart illustrating a method of supplying power from a power supplying apparatus to a display apparatus including a display panel having a plurality of pixels having OLEDs, according to an exemplary embodiment; and 
         FIG. 8  is a flowchart illustrating a method of supplying power from a power supplying apparatus to a display apparatus, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Exemplary embodiments are described in greater detail with reference to the accompanying drawings. 
     In the following description, the same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. Thus, it is apparent that the exemplary embodiments can be carried out without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the exemplary embodiments with unnecessary detail. 
       FIG. 2  is a block diagram of an organic light-emitting diode (OLED) display apparatus according to an exemplary embodiment. 
     Referring to  FIG. 2 , the OLED display apparatus includes a power supplier  210 , a rectifier  220 , a voltage level converter  230 , and a plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n. The OLED display apparatus may be realized as various types of apparatuses having display units like a TV, a portable phone, a personal digital assistant (PDA), a notebook PC, a monitor, a tablet PC, an electronic book (e-book), an electronic frame, a kiosk, etc. 
     The power supplier  210  supplies a voltage for driving the OLED display apparatus. The power supplier  210  may supply power to the components  240 - 1 ,  240 - 2 , . . . , and  240 -n of the OLED display apparatus by using an alternating current (AC) voltage input from an external source. 
     The rectifier  220  rectifies an input voltage supplied from the power supplier  210 . In detail, the rectifier  220  rectifies the AC voltage input from the power supplier  210  into a direct current (DC) voltage and transmits the DC voltage to the voltage level converter  230 . The rectifier  220  may include a rectifier circuit (not shown) and a power factor correction (PFC) unit  221 . In other words, the rectifier  220  corrects a power factor of the input voltage, which is the AC voltage input from the power supplier  210 , through the rectifier circuit and the PFC unit  221 . In detail, if the AC voltage is input from the power supplier  210 , the rectifier circuit rectifies the input AC voltage into the DC voltage. The PFC unit  221  may correct the power factor of the rectified DC voltage and output the DC voltage having the corrected power factor to the voltage level converter  230 , and an output of the PFC unit  221  may be about 400 V. 
     In addition, the PFC unit  221  is added as a power saving circuit to improve efficiency of power supplied to the OLED display apparatus and may adjust power supplied to components such as a transformer, a stabilizer, etc. which may instantaneously leak power. In other words, the PFC unit  221  may reduce power consumption and prevent a temperature from rising due to a change of a current into heat to improve power efficiency. In detail, the PFC unit  221  may include an inductor, a diode, a capacitor, and a switching means. Here, the inductor and the capacitor may be respectively connected to both ends of the diode, and the switching means may be connected to a contact node between the inductor and the diode. The switching means may be used as a transistor. A detailed circuit diagram of the PFC unit  221  is a well-known technology, and thus its detailed description and circuit diagram will be omitted in the present exemplary embodiment. Also, the PFC unit  221  may be a boost topology. 
     The voltage level converter  230  converts a level of the input voltage rectified by the rectifier  220 , i.e., a level of the DC voltage, and commonly supplies the input voltage to the plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n. The voltage level converter  230  may include a DC-DC converter (not shown) and thus may convert the DC voltage input from the rectifier  220  into a DC voltage having a preset level through the DC-DC converter and output the DC voltage having the preset level. 
     In detail, the voltage level converter  230  may convert the DC voltage input from the rectifier  220  into a voltage level for driving a display panel and commonly provide the voltage level to the components  240 - 1 ,  240 - 2 , . . . , and  240 -n. Here, the display panel may include a plurality of pixels having self-emission elements. Here, the self-emission elements may be realized as organic light-emitting diodes (OLEDs). 
     In general, an organic light-emitting display uses OLEDs using a light emission of an organic material and may drive N*M organic light-emitting cells arranged in a matrix by using a voltage or a current to display an image. Here, the organic light-emitting cells have diode characteristics and thus are referred to as OLEDs, and have structures of anodes, organic thin film transistors (TFTs), and cathode electrode layers. The OLEDs may be driven at a low driving voltage between about 12V and about 15V. Therefore, a voltage level for driving a display panel according to the present exemplary embodiment may be a voltage level (between 12V and 15V) for driving OLEDs forming pixels of the display panel. In other words, the voltage level converter  230  equally supplies a DC voltage having a voltage level for driving the OLEDs to the plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n. 
     The plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n operate the OLED display apparatus, e.g., may include at least one from among a display panel, an audio amplifier, an interface module, a communication interface module, and a sub Micom. 
     According to another exemplary embodiment , the OLED display apparatus may further include a controller  250  which controls overall operations of elements of the OLED display apparatus. The controller  250  controls turning on/off of the PFC unit  221  of the rectifier  220  according to operation states of the plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n. In detail, when the display panel performs a data voltage charging operation, the controller  250  may turn off the PFC unit  221 . When the display panel performs a light emitting operation, the controller  250  may turn on the PFC unit  221 . 
     The controller  250  detects a level of the DC current supplied to the display panel and, if the detected level of the DC voltage is a first voltage level, determines that the display panel performs the data voltage charging operation in order to turn off the PFC unit  221 . If the detected level of the DC voltage is a second voltage level, the controller  250  determines that the display panel performs the light-emitting operation in order to turn on the PFC unit  221 . 
     Here, a data voltage charging section in which the display panel performs the data voltage charging operation may be a section in which a scan driver  280  of a display apparatus that is the organic light-emitting display supplies a scan signal through a plurality of scan lines S 1 , S 2 , . . . , and Sn to turn on a switching transistor T 1  and a data driver  270  of the display apparatus supplies a data signal through a plurality of data lines D 1 , D 2 , . . . , and Dm to charge a capacitor C included in a plurality of pixels. Here, the capacitor C stores the supplied data signal as a data voltage. 
     A voltage ELVDD supplied from the voltage level converter  230  to the plurality of pixels of the display panel for the data voltage charging section may be the first voltage level. A light-emitting section in which the display panel performs the light-emitting operation may be a section in which the scan driver  280  of the display apparatus which is the organic light-emitting display cuts the scan signal supplied through the plurality of scan lines S 1 , S 2 , . . . , and Sn and supplies a voltage having a predetermined level through the voltage ELVDD to allow a driving transistor T 2  to generate a driving current corresponding to the data voltage stored in the capacitor C and a threshold voltage in order to emit light from the OLEDs emit. Here, the OLEDs emit the light in response to the driving current. 
     The voltage ELVDD supplied from the voltage level converter  230  to the plurality of pixels of the display panel may be a second voltage level. In other words, the controller  250  may detect a level of the voltage ELVDD output from the voltage level converter  230  and, if the detected level of the voltage ELVDD is the first voltage level, determine that the voltage ELVDD is in the data voltage charging section. Also, the controller  250  may detect the level of the voltage ELVDD output from the voltage level converter  230  and, if the detected level is the second voltage level, may determine that the voltage ELVDD is in the light-emitting section. 
     If the controller  250  determines that the voltage ELVDD is in the data voltage charging section as described above, the controller  250  may turn off the PFC unit  221 . If the controller  250  determines that the voltage ELVDD is in the light-emitting section, the controller  250  may turn off the PFC unit  221 . In other words, the controller  250  may control a switching element of the PFC unit  221  to control turning on/off of the PFC unit  221 . 
     The controller  250  may turn off the PFC unit  221  in the data voltage charging section to obtain a gain by power consumed by the PFC unit  221  for the data voltage charging section. As described above, according to an exemplary embodiment, a current is not supplied to the OLEDs in the data voltage charging section but is supplied to the OLEDs only in the light-emitting section. Therefore, the PFC unit  221  operates even in the data voltage charging section to solve a problem of a conventional display apparatus which generates an unnecessary loss of power. 
     According to another exemplary embodiment, the controller  250  may turn on the PFC unit  221  before a preset time based on a time when the data voltage charging section ends. In other words, the controller  250  turns off the PFC unit  221  of the rectifier  220  for the data voltage charging section. In this case, the PFC unit  221  may include the capacitor C and thus may supply the voltage level converter  230  with a voltage with which the capacitor C has been charged. Therefore, a level of the charging voltage of the PFC unit  221  is reduced. The PFC unit  221  is turned on in the light-emitting section, and thus a time required to reach a preset voltage level may be checked through an output of the PFC unit  221 . Therefore, the controller  250  may turn on the PFC unit  221  before the preset time (i.e., before a time when a voltage level reaches a preset level at a starting time of the light-emitting section) from the time when the data voltage charging section ends. 
     According to another exemplary embodiment, if an output voltage of the PFC unit  221  is lower than or equal to a preset level when the PFC unit  221  is turned off, the controller  250  may determine that a preset time has elapsed and turn on the PFC unit  221 . In detail, if the output voltage of the PFC unit  221  is lower than or equal to a preset level Vmin for the data voltage charging section, power efficiency of the voltage level converter  230 , which has turned off the PFC unit  221 , may be lower than efficiency of power passing through the voltage level converter  230  when the PFC unit  221  is turned on. Therefore, if the output voltage of the PFC unit  221  is lower than or equal to the preset level Vmin, the PFC unit  221  may be switched to a turned-on state according to a control command of the controller  250 . 
     The elements of the display apparatus according to an exemplary embodiment have been described in detail. An operation characteristic of the PFC unit  221  will now be described in detail with reference to  FIG. 3 . 
       FIG. 3  is a timing diagram illustrating an operation characteristic of the PFC unit  221  according to an exemplary embodiment. 
     In detail, the timing diagram of  FIG. 3  may include a characteristic (a) of a voltage ELVDD, an operation characteristic (b) of the PFC unit  221 , and an output voltage (c) of the PFC unit  221 . 
     Referring to the characteristic (a) of the voltage ELVDD, the voltage ELVDD is applied to have a second voltage level in a light-emitting section and a first voltage level in a data voltage charging section. The second voltage level in the light-emitting section is higher than the first voltage level in the data voltage charging section. 
     For the data voltage charging section, the scan driver  280  of the display apparatus which is the organic light-emitting display may supply a scan signal through the plurality of scan lines S 1 , S 2 , . . . , and Sn to turn on the switching transistor T 1 . Also, the data driver  270  of the display apparatus may supply a data signal through the plurality of data lines D 1 , D 2 , . . . , and Dm to charge the capacitor C of the plurality of pixels. 
     For the light-emitting section, the scan driver  280  of the display apparatus may cut the scan signal supplied through the plurality of scan lines S 1 , S 2 , . . . , and Sn and supply a voltage having a predetermined level through the voltage ELVDD to allow the driving transistor T 2  to generate a driving current corresponding to a data voltage stored in the capacitor C and a threshold voltage in order to emit light from OLEDs. Here, the OLEDs may emit the light in response to the driving current. 
     Referring to the operation characteristic (b) of the PFC unit  221 , the PFC unit  221  is turned off in the data voltage charging section in which a level of a DC voltage supplied to a display panel is a first voltage level. However, the PFC unit  221  is turned on in the light-emitting section in which the level of the DC voltage supplied to the display panel is a second voltage level. Also, the PFC unit  221  is turned on before a preset time from a time when the data voltage charging section ends. 
     Referring to the output voltage (c) of the PFC unit  221  if the PFC unit  221  is turned on, a predetermined DC voltage of the PFC unit  221  is supplied. If the PFC unit  221  is turned off, the PFC unit  221  includes the capacitor C and thus supplies the voltage level converter  230  with a voltage with which the capacitor C is charged. Therefore, a level of the charging voltage of the PFC unit  221  is lowered. 
     However, the output voltage of the PFC unit  221  may not be lower than or equal to the preset level Vmin. In other words, if the output voltage of the PFC unit  221  is lower than or equal to the preset level Vmin for the data voltage charging section, power efficiency of the voltage level converter  230 , which has turned off the PFC unit  221 , may be lower than efficiency of power passing through the voltage level converter  230  when the PFC unit  221  is turned on. Therefore, if the output voltage of the PFC unit  221  is lower than or equal to the preset level Vmin, the PFC unit  221  may be switched on according to a control command of the controller  250 . 
     Elements of a display apparatus which is an organic light-emitting display according to an exemplary embodiment will now be described in more detail with reference to  FIG. 4 . 
       FIG. 4  is a block diagram illustrating a detailed structure of a display apparatus according to an exemplary embodiment. 
     Before describing an operation of the display apparatus, the display apparatus may include a plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n. The component  240 - 1  of the plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n may be a display panel. Therefore, the component  240 - 1  will be described as a display panel in  FIG. 4 . 
     Referring to  FIG. 4 , the display apparatus includes an interface unit  260 , the display panel  240 - 1 , a controller  150 , the data driver  270 , the scan driver  280 , and a voltage driver  290 . 
     In general, the display apparatus which is an organic light-emitting display may be driven according to a passive matrix method or an active matrix method. The present exemplary embodiment explains that the display apparatus is driven according to the active matrix method. Also, the display apparatus which is the organic light-emitting display may display red (R), green (G), and blue (B) by using one of an independent pixel method, a color conversion method (CCM) and a color filtering method. The present exemplary embodiment explains that the display apparatus displays the R, G, and B through the independent pixel method. 
     The interface unit  260  may include a tuner which is to receive broadcast program contents from a broadcasting station, a Digital Visual Interface (DVI) connected to a recording medium player, a High Definition Multimedia Interface (HDMI) terminal, etc. The interface unit  260  receives an image signal having R, G, and B components from an external apparatus through these terminals and transmits the image signal to the controller  250 . If the image signal is received, the controller  250  transmits the received image signal to the data driver  270 . 
     The display panel  240 - 1  may include a plurality of pixels (hereinafter referred to as RGB pixels)  241 - 1  including OLEDs. The plurality of RGB pixels  241 - 1  may include self-emission elements which emit light in response to a flow of a current, a power supply source ELVDD which supplies the current to the self-emission elements, and driving transistors which control the current supplied to the self-emission elements. Here, the self-emission elements may be OLEDs, and the RGB pixels  241 - 1  may be respectively R, G, and B OLEDs. In other words, if the display apparatus displays RGB through the independent pixel method as described above, the display panel  240 - 1  may include a plurality of pixels which include R, G, and B OLEDs which are sequentially arranged. 
     The display panel  240 - 1  may include n scan lines S 1 , S 2 , . . . , and Sn which are arranged in a line direction to transmit a scan signal and m data lines D 1 , D 2 , . . . , and Dm which are arranged in a column direction to transmit a data signal. Also, the display panel  240 - 1  receives a driving power source ELVDD and a base power source ELVSS from the voltage driver  290  to be driven. For example, the display panel  240 - 1  may supply a current to the plurality of RGB pixels  241 - 1  through the scan signal, the data signal, the driving power source ELVDD, and the base power source ELVSS. Therefore, the plurality of RGB pixels  241 - 1  emit light in response to an amount of the current. 
     The data driver  270  receives the image signal having the R, G, and B components received from the controller  250  to generate the data signal. The data driver  270  is also connected to the data lines D 1 , D 2 , . . . , and Dm of the plurality of R, G, B pixels  241 - 1  to apply the data signal to the display panel  240 - 1 . 
     The scan driver  280  is an element which performs an operation of generating the scan signal and is connected to the scan lines S 1 , S 2 , . . . , and Sn to transmit the scan signal to a particular line of the display panel  240 - 1 . Therefore, the data signal output from the data driver  270  may be transmitted to the plurality of RGB pixels  241 - 1  to which the scan signal has been transmitted. 
     The voltage driver  290  includes a rectifier  220  and a voltage level converter  230  and transmits a generated driving voltage to the display panel  240 - 1  through the rectifier  220  and the voltage level converter  230 . In detail, the voltage driver  290  may supply an OLED driving voltage to the plurality of RGB pixels  241 - 1  by using a DC voltage generated through the rectifier  220  and the voltage level converter  230  which have been described with reference to  FIGS. 2 and 3 . In other words, the voltage driver  290  may supply the driving power source ELVDD and the base power source ELVSS to R, G, and B OLEDs of the plurality of RGB pixels  241 - 1 . 
     In detail, a PFC unit  221  of the rectifier  220  may correct a power factor of an input voltage and output the input voltage having the corrected power factor to the voltage level converter  230 . In other words, if an AC voltage is input, the rectifier  220  rectifies the input AC voltage to generate a DC voltage. If the DC voltage is generated, the PFC unit  221  corrects a power factor of the rectified AC voltage and output the AC voltage having the corrected power factor to the voltage level converter  230 . 
     The voltage level converter  230  converts the AC voltage output from the PFC unit  221  into at least one DC voltage. The voltage level converter  230  may also supply at least one DC voltage to the display panel  240 - 1 . The scan driver  280  which supplies the DC voltage to the display panel  240 - 1  through the rectifier  220  and the voltage level converter  230 , may supply the driving power source ELVDD and the base voltage source ELVSS to the plurality of RGB pixels  241 - 1  of the display panel  240 - 1  and may supply power to the elements of the display apparatus. 
     The controller  250  receives an image signal, a horizontal sync signal Hsync, a vertical sync signal Vsync, a main clock signal MCLK, etc. from an external apparatus through the interface unit  260  to generate an image data signal, a scan control signal, a data control signal, an emission control signal, etc. and transmits the image data signal, the scan control signal, the data control signal, the emission control signal, etc. to the display panel  240 - 1 , the data driver  270 , the scan driver  280 , and the voltage driver  290 . Detailed structures of these signals are obvious to those skilled in the art, and thus their detailed descriptions will be omitted. 
     The controller  250  which controls the elements of the display apparatus may control the rectifier  220  of the voltage driver  290  according to an operation state of the display panel  240 - 1 . In detail, the controller  250  may turn off the PFC unit  221  of the rectifier  220  when the display panel  240 - 1  performs a data voltage charging operation but may turn on the PFC unit  221  when the display panel  240 - 1  performs a light emitting operation. In other words, if the controller  250  detects a level of a voltage ELVDD output from the voltage level converter  230  and, if the detected voltage level is a first voltage level, determines that the voltage ELVDD is in a data voltage charting section. If the detected voltage level is a second voltage level, the controller  250  determines that the voltage ELVDD is in a light emitting section. 
     If the controller  250  determines that the voltage ELVDD is in the data voltage charging section or the light emitting section according to the detected voltage level, the controller  250  may control a switching element of the PFC unit  221  to turn on/off the PFC unit  221 . 
     The controller  250  may turn on the PFC unit  221  before a preset time from a time when the data voltage charging section ends or may turn on the PFC unit  221  if an output voltage of the PFC unit  221  is lower than or equal to a preset level when the PFC unit  221  is turned off. As described above, the controller  250  may control the switching element of the PFC unit  221  to perform an operation of turning on/off the PFC unit  221  in order to obtain a gain by power consumed by the PFC unit  221  for the data voltage charging section. Therefore, power efficiency may be more improved than in a conventional display apparatus. The operation of the controller  250  of controlling the switching element of the PFC unit  221  to turn on/off the PFC unit  221  has been described in detail with reference to  FIGS. 2 and 3 , and thus its detailed descriptions will be omitted hereinafter. 
     The plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n may include infrared (IR) receiving modules, which are to receive an IR signal from a remote control apparatus, etc. The plurality of components  240 - 1 ,  240 - 2 , . . . , and  240 -n are driven by using the DC voltage input from the voltage level converter  230  of the voltage driver  290 . However, the components  240 - 1 ,  240 - 2 , . . . , and  240 -n may be driven by a voltage lower than an OLED driving voltage, such as 1.1V. 1.8V, 3.3V, 5V, or the like. In this case, the components  240 - 1 ,  240 - 2 , . . . , and  240 -n may include additional voltage lowering circuit (not shown), which lower the input DC voltage, in order to lower a voltage supplied from the voltage level converter  230  to a used voltage level. 
     The voltage level converter  230  may further include a switching mode power supply (SMPS). In other words, the voltage level converter  230  may convert a DC voltage having an OLED driving voltage level into a voltage required by the components  240 - 2 , . . . , and  240 -n except the component  240 - 1  which is the display panel, through the SMPS and output the voltage. The SMPS may include a voltage converter to induce a DC voltage having various levels to a secondary winding wire according to a winding wire ratio if a DC voltage having a level for driving OLEDs is applied to a primary winding wire of the voltage converter. Through this process, the SMPS may output various DC voltages of 1.1V, 1.8v, 3.3V, 5V, etc. to supply the various DC voltages to the components  240 - 1 ,  240 - 2 , . . . , and  240 -n. 
     According to an exemplary embodiment, as described above, a driving voltage may be further efficiently applied to the components  240 - 1 ,  240 - 2 , . . . , and  240 -n of the display apparatus by using one DC-DC converter. 
     An OLED is a light-emitting device which emits light at a driving voltage between 12V and 15V. Therefore, if the RGB pixel  241 - 1  of the display panel  240 - 1  is realized as an OLED, and a liquid crystal display (LCD) emits light by using a backlight unit, the component  240 - 1  which is the display panel may be driven at a voltage lower than a voltage between 200V and 300V. The components  240 - 1 ,  240 - 2 , . . . , and  240 -n of the display apparatus are generally driven at a voltage lower than or equal to an OLED driving voltage. In other words, since the OLED driving voltage is similar to the voltage for driving the components  240 - 1 ,  240 - 2 , . . . , and  240 -n, the driving voltage of the components  240 - 1 ,  240 - 2 , . . . , and  240 -n may be generated through one DC-DC converter. 
     A circuit configuration of the RGB pixel  241 - 1  of the display panel  240 - 1  of the display apparatus will now be described in detail. 
       FIG. 5  is a circuit diagram of an RGB pixel of a display panel according to an exemplary embodiment. 
     Referring to  FIG. 5 , each RGB pixel  241 - 1  of the display panel  240 - 1  includes an OLED and a pixel circuit  241 - 1 ′ which is to supply a current to the OLED. 
     An anode of the OLED is connected to the pixel circuit  241 - 1 ′, and a cathode of the OLED is connected to a second power source ELVSS. The OLED generates light having predetermined brightness in response to the current supplied from the pixel circuit  241 - 1 ′. As shown in  FIG. 5 , the pixel circuit  241 - 1 ′ of the RGB pixel  241 - 1  may include three transistors, i.e., first, second, and third transistors, M 1 , M 2 , and M 3 , and two capacitors, i.e., first and second capacitors, C 1  and C 2 . Here, a gate electrode of the first transistor M 1  is connected to a scan line S, a first electrode of the first transistor M 1  is connected to a data line D, and a second electrode of the first transistor M 1  is connected to a first node N 1 . 
     In other words, a scan signal Scan (b) is input into the gate electrode of the first transistor M 1 , and a data signal Data (t) is input into the first electrode of the first transistor M 1 . Also, a gate electrode of the second transistor M 2  is connected to a second node N 2 , a first electrode of the second transistor M 2  is connected to a first power source ELVDD(t), and a second power source is connected to an anode of an OLED. Here, the second transistor M 2  operates as a driving transistor. 
     The first capacitor C 1  is connected between the first node N 1  and the first electrode of the second transistor M 2 , i.e., the first power source ELVDD (t), and the second capacitor C 2  is connected between the first node N 1  and the second node N 2 . Also, a gate electrode of the third transistor M 3  is connected to a control line GC, a first electrode of the third transistor M 3  is connected to the gate electrode of the second transistor M 2 , and a second electrode of the third transistor M 3  is connected to the anode of the OLED, i.e., the second electrode of the second transistor M 2 . 
     Therefore, a control signal GC (t) is input into the gate electrode of the third transistor M 3 . If the third transistor M 3  is turned on, the second transistor M 2  is connected to a diode, and a cathode of the OLED is connected to the second power source ELVSS (t). 
     A power supplying apparatus which supplies power to a display panel including a plurality of RGB pixels including OLEDs according to exemplary embodiments will now be described in detail. 
       FIG. 6  is a block diagram of a power supplying apparatus which supplies power to a display panel including a plurality of RGB pixels including OLEDs according to an exemplary embodiment. 
     Referring to  FIG. 6 , the power supplying apparatus includes a PFC unit  610 , a DC-DC converter  620 , and a controller  630 . As shown in  FIG. 4 , the power supplying apparatus may be used in a display apparatus including a display panel  240 - 1  including a plurality of pixels including OLEDs. Here, the display apparatus may be an organic light-emitting display. 
     The power supplying apparatus which supplies power to the display panel  240 - 1  of the display apparatus may supply power sources ELVDD and ELVSS. Here, the power supplying apparatus may supply the power sources ELVDD and ELVSS and may supply a driving power source to all elements of the display apparatus requiring a power source. 
     The PFC unit  610  corrects a power factor of an input voltage and outputs the input voltage having the corrected power factor to the DC-DC converter  620 . In other words, if an input AC voltage is rectified to be generated as a DC voltage through the rectifier  220  as illustrated in  FIG. 3  or  4 , the PFC unit  610  may correct a power factor of the rectified DC voltage and output the DC voltage having the corrected power factor to the DC-DC converter  620 . In general, an output of the PFC unit  610  may be about 400V in the display apparatus which is an organic light-emitting display. 
     Here, the PFC unit  610  is a power saving circuit added to improve power efficiency of the power supplying apparatus and adjusts power supplied to components, such as a transformer, a stabilizer, etc., which may instantaneously leak power. In other words, the PFC unit  610  may reduce power consumption and prevent a temperature from rising due to a change of a current into heat in order to improve power efficiency. 
     In detail, the PFC unit  610  may include an inductor, a diode, a capacitor, and a switching means. Here, the inductor and the capacitor may be respectively connected to both ends of the diode, and the switching means may be connected to a contact node between the inductor and the diode and may be used as a transistor. A detailed circuit diagram of the PFC unit  610  will be omitted. The PFC unit  610  may be a boost topology. 
     The DC-DC converter  620  converts a level of the DC voltage output from the PFC unit  610 . As shown in  FIG. 4 , the DC-DC converter  620  may supply the DC voltage having the converted level to the display panel  240 - 1  of the display apparatus. Here, the DC-DC converter  620  may be constituted by using a well-known DC-DC converter circuit. The controller  630  controls an overall operation of the power supplying apparatus. In detail, the controller  630  may control the PFC unit  610  and the DC-DC converter  620 . 
     The controller  630  may control turning on/off of the PFC unit  610  according to an operation state of the display panel  240 - 1 . In other words, the controller  630  may turn off the PFC unit  610  when the display panel  240 - 1  performs a data voltage charging operation. However, the controller  630  may turn on the PFC unit  610  when the display panel  240 - 1  performs a light-emitting operation. 
     Here, as shown in  FIG. 4 , a data voltage charging section in which the display panel  240 - 1  performs the data voltage charging operation refers to a section in which the scan driver  280  of the display apparatus supplies a scan signal through a plurality of scan lines S 1 , S 2 , . . . , Sn- 1 , and Sn to turn on a switching transistor T 1 , and the data driver  270  of the display apparatus supplies a data signal through a plurality of data lines D 1 , D 2 , Dm- 1 , and Dm to charge a capacitor C of a plurality of pixels. Here, the capacitor C stores the supplied data signal as a data voltage. 
     A voltage ELVDD supplied from the DC-DC converter  620  to the plurality of pixels of the display panel  240 - 1  for the data voltage charging section may be a first voltage level. 
     The light-emitting section in which the display panel  240 - 1  emits light refers to a section in which the scan driver  280  of the display apparatus cuts the scan signal supplied through the plurality of scan lines S 1 , S 2 , . . . , and Sn- 1 , and Sn and supplies a voltage having a predetermined level through the voltage ELVDD to allow a driving transistor T 2  to generate a driving current corresponding to the data voltage stored in the capacitor C and a threshold voltage in order to emit light from an OLED. Here, the OLED emits the light in response to the driving current. 
     The voltage ELVDD supplied from the DC-DC converter  620  to the plurality of pixels of the display panel  240 - 1  for the light-emitting section may be a second voltage level. In other words, the controller  630  may detect a level of the voltage ELVDD output from the DC-DC converter  620  and, if the detected voltage level is a first voltage level, may determine that the voltage ELVDD is in the data voltage charging section. The controller  630  may detect a level of the voltage ELVDD output from the DC-DC converter  620  and, if the detected voltage level is a second voltage level, may determine that the voltage ELVDD is in the light emission section. 
     If the controller  630  determines that the voltage ELVDD is in the data voltage charging section, the controller  630  may turn off the PFC unit  610 . If the controller  630  determines that the voltage ELVDD is in the emission section, the controller  630  may turn on the PFC unit  610 . In other words, the controller  630  may control the switching element of the PFC unit  610  to control turning on/off of the PFC unit  610 . 
     As described above, the controller  630  may control the PFC unit  610  to be turned off in the data voltage charging section to obtain a gain in power consumed by the PFC unit  610  for the data voltage charting section. In other words, if a conventional voltage supplying apparatus is applied, the conventional voltage supplying apparatus does not reflect a driving characteristic of a display apparatus which is an organic light-emitting apparatus (i.e., a characteristic by which a current is not supplied to an OLED in the data voltage charging section but is supplied to the OLED in the emission section). Therefore, the PFC unit  610  operates in the data voltage charging section, and thus an unnecessary loss of power occurs. Accordingly, the power supplying apparatus according to an exemplary embodiment may improve power efficiency. 
     The controller  630  may turn on the PFC unit  610  before a preset time from a time when the data voltage charging section ends. In other words, the controller  630  turns off the PFC unit  610  for the data voltage charging section. In this case, the PFC unit  610  includes a capacitor and supplies a voltage, with which the capacitor is charged, to the DC-DC converter  620 . Therefore, a level of the charging voltage of the PFC unit  610  is lowered. If the voltage ELVDD reaches the light-emitting section, the PFC unit  610  is turned on, and thus a time is required for an output of the PFC unit  610  to reach a preset voltage level. Therefore, the controller  630  may turn on the PFC unit  610  before a preset time (i.e., before a time when a voltage level reaches a preset level at a starting time of the light-emitting section) from the time when the data voltage charging section ends. 
     If the output voltage of the PFC unit  610  is lower than or equal to a preset level when the PFC unit  610  is turned on, the controller  630  may control the PFC unit  610  to be turned on. In other words, if the output voltage of the PFC unit  610  is lower than or equal to a preset level Vmin for the data voltage charging section, power efficiency of the DC-DC converter  620  which has turned on the PFC unit  610  may be lower than efficiency of power passing through the DC-DC converter  620  when the PFC. unit  610  is turned on. Therefore, if the output voltage of the PFC unit  610  is lower than or equal to the preset level Vmin, the controller  630  may control the PFC unit  610  to be turned on. 
     The elements of the display apparatus and the power supplying apparatus according to an exemplary embodiment have been described in detail. A method of supplying from a power supplying apparatus to a display panel including a plurality of pixels including OLEDs of a display apparatus will now be described in detail. 
       FIG. 7  is a flowchart illustrating a method of supplying from a power supplying apparatus to a display panel including a plurality of pixels including OLEDs of a display apparatus according to an exemplary embodiment. 
     Referring to  FIG. 7 , in operation S 710 , the power supplying apparatus corrects a power factor of an input voltage by using a PFC unit. In operation S 720 , the power supplying apparatus converts a level of a DC voltage, which is output through the correction of the power factor of the input voltage, and supplies the DC voltage having the converted level to the display panel. In operation S 730 , the power supplying apparatus controls the PFC unit to be turned on/off according to an operation state of the display panel. The method will now be described in more detail with reference to  FIG. 8 . 
       FIG. 8  is a flowchart illustrating a method of supplying power from a power supplying apparatus to a display apparatus according to an exemplary embodiment. 
     Referring to  FIG. 8 , in operation S 810 , the power supplying apparatus corrects a power factor of an input voltage through a PFC unit. If a DC voltage of the input voltage is output through the correction of the power factor of the input voltage, the power supplying apparatus converts a level of the output DC voltage and supplies the DC voltage having the converted level to a display panel of the display apparatus in operation S 820 . In operation S 830 , the power supplying apparatus detects a level of the DC voltage supplied to the display panel. In operation S 840 , the power supplying apparatus checks whether the detected level of the DC voltage is a first level. If it is checked that the detected level of the DC voltage is the first level, the power supplying apparatus determines that the display panel performs a data voltage charging operation to turn off the PFC unit in operation S 850 . If it is checked that the detected level of the DC voltage is not the first level, the power supplying apparatus determines that the detected level of the DC voltage is a second level. Therefore, in operation  5860 , the power supplying apparatus determines that the display panel performs a light-emitting operation to turn on the PFC unit. 
     As described above, a power supplying apparatus, which turns on/off a PFC unit according to a level of a DC voltage supplied to a display panel, may turn on the PFC unit before a preset time from a time when a data voltage charging section ends. Also, if an output voltage of the PFC unit is lower than or equal to a preset level when the PFC unit is turned off, the power supplying apparatus may turn on the PFC unit. 
     According to the above-described various exemplary embodiments, a power supplying apparatus turns off a PFC unit in a data voltage charging section to obtain a gain in power consumed by the PFC unit for the data voltage charging section. Therefore, power efficiency may be improved. A power supplying apparatus, a power supplying method, and an organic light-emitting display according to exemplary embodiments have been described in detail. 
     The foregoing exemplary embodiments and advantages are merely exemplary and are not to be construed as limiting. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.