Patent Publication Number: US-2023154381-A1

Title: Display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Korean Patent Application No. KR 10-2021-0158721, filed on Nov. 17, 2021, in the Korean Intellectual Property Office, the entire disclosure of which is hereby expressly incorporated by reference into the present application. 
     BACKGROUND 
     Field 
     The present disclosure relates to a display device including a plurality of power converters. 
     Description of the Related Art 
     As the information-oriented society is implemented, there is an increasing demand for various display devices for displaying images. Recently, various display devices such as a liquid crystal display (LCD) device, a plasma display panel (PDP), and an organic light-emitting display (OLED) device have been used. 
     Further, the display device includes a power supply that generates drive power required for operation. The power supply includes a plurality of power converters that converts input power, which is supplied from an external system, into drive power required to operate the display device. Further, the input power is direct current power, and the drive power, which is the output power, is also direct current power. Therefore, the power supply can be a DC/DC power converter. 
     Meanwhile, the external systems connected to the power supply can be various types of power system such as a power battery and a power adapter. Further, the input power supplied from the power battery can be lower than the input power supplied from the power adapter. For example, a level of the input power supplied to the power supply can vary depending on situations. 
     Power conversion efficiency of the power supply varies as the input power of the power supply varies as described above. For this reason, there can be a limitation in that the efficiency of the power supply may deteriorate, which can increase the power consumption of the display device. 
     SUMMARY OF THE DISCLOSURE 
     An object to be achieved by the present disclosure is to provide a display device in which power conversion efficiency of a power supply is improved. 
     Another object to be achieved by the present disclosure is to provide a display device capable of changing a boost voltage of the power supply. 
     Objects of the present disclosure are not limited to the above-mentioned objects, and other objects, which are not mentioned above, can be clearly understood by those skilled in the art from the following descriptions. 
     According to an aspect of the present disclosure, a display device includes a display panel having plurality of pixels disposed on a substrate, and a power supplier configured to supply a driving voltage to the display panel. The power supplier can include a first converter configured to receive an input voltage supplied from an external system and convert the input voltage into a boost voltage, a second converter configured to convert the boost voltage into the driving voltage, a first feedback unit configured to output a first pulse width modulation (PWM) signal to the first converter so that the boost voltage is proportional to a first reference voltage, a second feedback unit configured to output a second PWM signal to the second converter so that the driving voltage is proportional to a second reference voltage, and a reference voltage calculator configured to receive the input voltage and the driving voltage and supply the first reference voltage to the first feedback unit. Therefore, it is possible to improve the power conversion efficiency of the power supplier. 
     According to another aspect of the present disclosure, a display device includes a display panel having a plurality of pixels disposed on a substrate, and a power supplier configured to supply a driving voltage to the display panel. The power supplier can include a first converter configured to convert an input voltage, which is supplied from an external system, into a boost voltage, a second converter configured to convert the boost voltage into the driving voltage, a first feedback unit configured to control the first converter so that the first converter outputs the boost voltage, a second feedback unit configured to control the second converter so that the second converter outputs the driving voltage, and a feedback voltage calculator configured to calculate a feedback voltage from the input voltage and the driving voltage. 
     The first feedback unit can include a plurality of resistors, a first amplifier, and a first PWM generator. A first reference voltage is applied to a non-inverting terminal of the first amplifier, an inverting terminal of the first amplifier is connected to the feedback voltage calculator through any one of the plurality of resistors, and the first PWM generator outputs a first PWM signal to the first converter so that the boost voltage is proportional to the first reference voltage. Therefore, it is possible to improve the power conversion efficiency of the power supplier. 
     Other matters of the exemplary embodiments are included in the detailed description and the drawings. 
     The present disclosure can increase final efficiency of the power supplier by changing the boosted voltage depending on the input voltage and the driving voltage. 
     The present disclosure can minimize power consumption caused by a ripple by suppressing the occurrence of the ripple by bypassing the input voltage as the boost voltage. 
     The effects according to the present disclosure are not limited to the contents exemplified above, and more various effects are included in the present specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a block diagram for explaining a display device according to an embodiment of the present disclosure; 
         FIG.  2    is a block diagram of a power supplier of the display device according to the embodiment of the present disclosure; 
         FIG.  3    is a circuit diagram of the power supplier of the display device according to the embodiment of the present disclosure; 
         FIG.  4    is a top plan view illustrating a printed circuit board having the power supplier of the display device according to the embodiment of the present disclosure; 
         FIG.  5    is a circuit diagram of a first reference voltage output part of the display device according to the embodiment of the present disclosure; 
         FIG.  6    is a voltage waveform diagram of the display device according to the embodiment of the present disclosure; 
         FIG.  7    is a block diagram of a power supplier of a display device according to another embodiment of the present disclosure; 
         FIG.  8    is a circuit diagram of the power supplier of the display device according to another embodiment of the present disclosure; 
         FIG.  9    is a voltage waveform diagram of the display device according to another embodiment of the present disclosure; 
         FIG.  10    is a block diagram of the power supplier of the display device according to still another embodiment of the present disclosure; 
         FIG.  11    is a circuit diagram of a power supplier of a display device according to still another embodiment of the present disclosure; 
         FIG.  12    is a block diagram of a feedback voltage calculator of the display device according to still another embodiment of the present disclosure; 
         FIG.  13 A  is a circuit diagram of a first feedback voltage converter of the display device according to still another embodiment of the present disclosure; 
         FIG.  13 B  is a circuit diagram of a second feedback voltage converter of the display device according to still another embodiment of the present disclosure; and 
         FIG.  14    is a circuit diagram of a feedback voltage output part of the display device according to still another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Advantages and characteristics of the present disclosure and a method of achieving the advantages and characteristics will be clear by referring to exemplary embodiments described below in detail together with the accompanying drawings. However, the present disclosure is not limited to the exemplary embodiments disclosed herein but will be implemented in various forms. The exemplary embodiments are provided by way of example only so that those skilled in the art can fully understand the disclosures of the present disclosure and the scope of the present disclosure. Therefore, the present disclosure will be defined only by the scope of the appended claims. 
     The shapes, sizes, ratios, angles, numbers, and the like illustrated in the accompanying drawings for describing the exemplary embodiments of the present disclosure are merely examples, and the present disclosure is not limited thereto. Like reference numerals generally denote like elements throughout the specification. Further, in the following description of the present disclosure, a detailed explanation of known related technologies can be omitted to avoid unnecessarily obscuring the subject matter of the present disclosure. The terms such as “including,” “having,” and “consist of” used herein are generally intended to allow other components to be added unless the terms are used with the term “only”. Any references to singular can include plural unless expressly stated otherwise. 
     Components are interpreted to include an ordinary error range even if not expressly stated. 
     When the position relation between two parts is described using the terms such as “on”, “above”, “below”, and “next”, one or more parts can be positioned between the two parts unless the terms are used with the term “immediately” or “directly”. 
     When an element or layer is disposed “on” another element or layer, another layer or another element can be interposed directly on the other element or therebetween. 
     Although the terms “first”, “second”, and the like are used for describing various components, these components are not confined by these terms. These terms are merely used for distinguishing one component from the other components, and may not define order. Therefore, a first component to be mentioned below can be a second component in a technical concept of the present disclosure. 
     Like reference numerals generally denote like elements throughout the specification. 
     A size and a thickness of each component illustrated in the drawing are illustrated for convenience of description, and the present disclosure is not limited to the size and the thickness of the component illustrated. 
     The features of various embodiments of the present disclosure can be partially or entirely adhered to or combined with each other and can be interlocked and operated in technically various ways, and the embodiments can be carried out independently of or in association with each other. Further, all components of each display device according to all embodiments of the present disclosure are operatively coupled and configured. 
       FIG.  1    is a block diagram for explaining a display device according to an embodiment of the present disclosure. 
     Referring to  FIG.  1   , a display device  100  includes a display panel  110 , a gate drive part (gate driver)  120 , a data drive part (data driver)  130 , and a power supplier (power supplying part)  140 . 
     The display panel  110  includes a substrate made of glass or plastic, and a plurality of gate lines GL and a plurality of data lines DL that intersect one another on the substrate. A plurality of pixels PX is provided at intersection points between the plurality of gate line GL and the plurality of data lines DL. Further, an area in which the plurality of pixels PX for implementing images is disposed can be referred to as a display area. An area disposed at an outer periphery of the display area and having no pixel PX can be referred to as a non-display area. 
     The plurality of pixels PX of the display panel  110  can each have at least one thin-film transistor. 
     Further, in a case in which the display device  100  according to the embodiment of the present disclosure is an electroluminescent display device, electric currents are applied to electroluminescent diodes provided in the plurality of pixels PX, and emitted electrons and holes are combined, such that excitons are produced. Further, the excitons emit light, thereby implementing gradations of the display device  100 . 
     However, the display device  100  according to the embodiment of the present disclosure is not limited to an electroluminescent display device. The display device  100  can be one of the display devices, such as a liquid crystal display device, having various shapes. 
     The gate drive part  120  sequentially supplies the gate line GL with gate voltages such as an ON-voltage or an OFF-voltage in response to the gate control signal outputted from a timing controller. 
     The gate control signals include a gate start pulse, a gate shift clock, a gate output enable signal, and the like. 
     The gate start pulse controls operation start timing of one or more gate circuits that constitute the gate drive part  120 . The gate shift clock is a clock signal inputted in common to the one or more gate circuits and controls shift timing of a scan signal (gate pulse). The gate output enable signal assigns timing information of the one or more gate circuits. 
     The gate drive part  120  can be positioned only at one side of the display panel  110  or at two opposite sides of the display panel  110  in some instances depending on driving methods. 
     The gate drive part  120  can include a shift register, a level shifter, and the like. 
     Based on the data control signal, the data drive part  130  converts the image data, which are received from the timing controller, into the analog data voltages Vdata and outputs the analog data voltages Vdata to the data line DL. 
     The data control signal includes a source start pulse, a source sampling clock, a source output enable signal, and the like. 
     The source start pulse controls data sampling start timing of the one or more data circuits that constitute the data drive part  130 . The source sampling clock is a clock signal for controlling the sampling timing of data for each data circuit. The source output enable signal controls output timing of the data drive part  130 . 
     The data drive part  130  can be connected to a bonding pad of the display panel  110  by a tape automated bonding method or a chip-on glass method or disposed directly on the display panel  110 . In some instances, the data drive part  130  can be integrated on the display panel  110 . 
     The data drive part  130  can include an output buffer, a digital analog converter (DAC), and a logic part including various circuits such as a level shifter and a latch part. 
     The power supplier  140  can convert an input voltage, which is supplied from an external system, into a driving voltage required to operate the display device  100 . Specifically, the power supplier  140  converts the input voltage and outputs a gate high-potential voltage VGH, a source high-potential voltage SVDD, and a drive high-potential voltage EVDD. The gate high-potential voltage VGH is a voltage used to generate a gate voltage and is supplied to the gate drive part  120 . The source high-potential voltage SVDD is a high-potential power voltage applied to a gamma voltage divider circuit of the data drive part  130  that generates gamma reference voltages. The source high-potential voltage is supplied to the data drive part  130 . The drive high-potential voltage EVDD is a voltage applied to an electroluminescent diode included in each of the plurality of pixels PX and is supplied to the plurality of pixels PX. 
       FIG.  2    is a block diagram of a power supplier of the display device according to the embodiment of the present disclosure. 
     Referring to  FIG.  2   , the power supplier  140  includes a first converter (boost converter)  141 , a second converter (buck converter)  142 , a first feedback unit (boost feedback)  143 , a second feedback unit (buck feedback)  144 , and a reference voltage calculator (Vref calculator)  145 . 
     The first converter  141  raises an input voltage Vin, which is supplied from the external system to a boost voltage Vbst. For example, the first converter  141  can be a boost converter or a step-up converter that converts the input voltage Vin into the boost voltage Vbst by raising the input voltage Vin. 
     The second converter  142  lowers the raised boost voltage Vbst to a driving voltage Vout required for the display device  100 . For example, the second converter  142  can be a buck converter or a step-down converter that converts the boost voltage Vbst into the driving voltage Vout by lowering the boost voltage Vbst. 
     The first feedback unit  143  senses and controls the boost voltage Vbst so that the first converter  141  outputs the constant boost voltage Vbst. For example, the first feedback unit  143  generates a first pulse width modulation (PWM) signal PWM1 and outputs the first PWM signal PWM1 to the first converter  141  so that the boost voltage Vbst can be maintained at a predetermined level in proportion to a first reference voltage Vref1. 
     The second feedback unit  144  senses and controls the driving voltage Vout so that the second converter  142  can maintain the constant driving voltage Vout. For example, the second feedback unit  144  generates a second PWM signal PWM2 and outputs the second PWM signal PWM2 to the second converter  142  so that the driving voltage Vout can be maintained at a predetermined level in accordance with a second reference voltage. 
     The reference voltage calculator  145  calculates the first reference voltage Vref1 and outputs the first reference voltage Vref1 to the first feedback unit  143  so that the power supplier  140  can operate in maximum efficiency. For example, the reference voltage calculator  145  receives the input voltage Vin and the driving voltage Vout, calculates the first reference voltage Vref1 in accordance with the input voltage Vin and the driving voltage Vout, and outputs the first reference voltage Vref1 to the first feedback unit  143 . 
     Hereinafter, specific circuit configurations of the first converter  141 , the second converter  142 , the first feedback unit  143 , the second feedback unit  144 , and the reference voltage calculator  145  will be described with reference to  FIG.  3   . 
       FIG.  3    is a circuit diagram of the power supplier of the display device according to the embodiment of the present disclosure. 
     Referring to  FIG.  3   , the first converter  141  includes a first inductor L 1 , a first diode D 1 , a first transistor T 1 , and a first capacitor C 1 . 
     The input voltage Vin is applied to one end of the first inductor L 1 , and the first diode D 1  and the first transistor T 1  are connected to the other end of the first inductor L 1 . Further, the first inductor L 1  is connected to an anode electrode of the first diode D 1 . The first capacitor C 1 , the second converter  142 , and the first feedback unit  143  are connected to a cathode electrode of the first diode D 1 . Further, a gate electrode of the first transistor T 1  is connected to the first feedback unit  143 . A source electrode of the first transistor T 1  is connected to the first inductor L 1  and the first diode D 1 . A drain electrode of the first transistor T 1  is grounded. 
     Therefore, the first PWM signal PWM1 outputted from the first feedback unit  143  controls the first transistor T 1 , such that the first converter  141  can generate the boost voltage Vbst by using the first inductor L 1  and the first diode D 1 . 
     Referring to  FIG.  3   , the second converter  142  includes a second inductor L 2 , a second transistor T 2 , a third transistor T 3 , and a second capacitor C 2 . 
     The boost voltage Vbst is applied to one end of the second inductor L 2  through the second transistor T 2 . The second capacitor T 2  is connected to the other end of the second inductor L 2 . Further, a gate electrode of the second transistor T 2  is connected to the second feedback unit  144 . A source electrode of the second transistor T 2  is connected to the first converter  141 . A drain electrode of the second transistor T 2  is connected to the second inductor L 2 . Further, a gate electrode of the third transistor T 3  is connected to the second feedback unit  144  through an inverter. A source electrode of the third transistor T 3  is connected to the second inductor L 2 . A drain electrode of the third transistor T 3  is grounded. 
     Therefore, the second PWM signal PWM2 outputted from the second feedback unit  144  controls the second transistor T 2  and the third transistor T 3 , such that the second converter  142  can generate the driving voltage Vout by using the second inductor L 2 . 
     Referring to  FIG.  3   , the first feedback unit  143  includes a plurality of resistors R1, R2, and R3, a third capacitor C 3 , a first amplifier AMP1, a first oscillator OSC  1 , a first comparator CP 1 , and a first PWM generator PG 1 . 
     The first resistor R1 and the second resistor R2 are connected in series. The first resistor R1 and the second resistor R2, which are connected in series, are connected between an output port of the first converter  141  and a grounding terminal. Therefore, the first resistor R1 and the second resistor R2, which are connected in series, serve as voltage distributors that distribute the boost voltage Vbst. Therefore, the boost voltage Vbst distributed between the first resistor R1 and the second resistor R2 can be expressed as R2/(R1+R2)*Vbst. 
     The first resistor R1 and the second resistor R2 can be connected to an inverting terminal of the first amplifier AMP1, and the distributed boost voltage (R2/(R1+R2)*Vbst) can be applied. Further, the reference voltage calculator  145  can be connected to a non-inverting terminal of the first amplifier AMP1, and the first reference voltage Vref1 can be applied. Further, because the voltage at the inverting terminal of the first amplifier AMP1 and the voltage at the non-inverting terminal of the first amplifier AMP1 are equal to each other, the first reference voltage Vref1 can be the distributed boost voltage (R2/(R1+R2)*Vbst). Further, the third resistor R3 and the third capacitor C 3 , which are connected in series, are connected to an output terminal of the first amplifier AMP1, thereby stabilizing an output voltage of the first amplifier AMP1. For example, the first amplifier AMP1 derives a difference value between the distributed boost voltage (R2/(R1+R2)*Vbst) and the first reference voltage Vref1 and outputs an amplified value of the difference value. 
     A first oscillator OSC 1  can be connected to the inverting terminal of the first comparator CP 1 , such that a triangular wave outputted from the first oscillator OSC 1  can be applied. Further, the first amplifier AMP1 can be connected to the non-inverting terminal of the first comparator CP 1 , such that an output value of the first amplifier AMP1 can be applied. Further, the first PWM generator PG 1  is connected to the output terminal of the first amplifier AMP1. For example, the first comparator CP 1  outputs, to the first PWM generator PG 1 , a result value made by comparing the output value of the first amplifier AMP1 with the triangular wave outputted from the first oscillator OSC 1 . 
     The first PWM generator PG 1  receives the output value of the first comparator CP 1  and outputs, to the first converter  141 , the first PWM signal PWM1 having a duty made by reflecting the output value of the first comparator CP 1 . Therefore, the first transistor T 1  of the first converter  141  performs an ON/OFF switching operation corresponding to the first PWM signal PWM1, such that the first converter  141  converts the input voltage Vin to the boost voltage Vbst in accordance with the duty of the first PWM signal PWM1. 
     Referring to  FIG.  3   , the second feedback unit  144  includes a plurality of resistors R4, R5, and R6, a fourth capacitor C 4 , a second amplifier AMP2, a second oscillator OSC  2 , a second comparator CP 2 , and a second PWM generator PG 2 . 
     The fourth resistor R4 and the fifth resistor R5 are connected in series. Further, the fourth resistor R4 and the fifth resistor R5, which are connected in series, are connected between an output port of the second converter  142  and the grounding terminal. Therefore, the fourth resistor R4 and the fifth resistor R5, which are connected in series, serve as voltage distributors that distribute the driving voltage Vout. Therefore, the driving voltage Vout distributed between the fourth resistor R4 and the fifth resistor R5 can be expressed as R5/(R4+R5)*Vout. 
     The fourth resistor R4 and the fifth resistor R5 are connected to an inverting terminal of the second amplifier AMP2, such that the distributed driving voltage (R5/(R4+R5)*Vout) can be applied. Further, a second reference voltage Vref2 for outputting the driving voltage Vout can be applied to a non-inverting terminal of the second amplifier AMP2. Because the voltage at the inverting terminal of the second amplifier AMP2 and the voltage at the non-inverting terminal of the second amplifier AMP2 are equal to each other, the second reference voltage Vref2 can be the distributed driving voltage (R5/(R4+R5)*Vout). Further, the sixth resistor R6 and the fourth capacitor C 4 , which are connected in series, are connected to an output terminal of the second amplifier AMP2, thereby stabilizing an output voltage of the second amplifier AMP2. For example, the second amplifier AMP2 derives a difference value between the distributed driving voltage (R5/(R4+R5)*Vout) and the second reference voltage Vref2 and outputs an amplified value of the difference value. 
     A second oscillator OSC 2  is connected to the inverting terminal of the second comparator CP 2 , such that a triangular wave outputted from the second oscillator OSC 2  can be applied. Further, the second amplifier AMP2 can be connected to the non-inverting terminal of the second comparator CP 2 , such that an output value of the second amplifier AMP2 can be applied. Further, the second PWM generator PG 2  is connected to the output terminal of the second amplifier AMP2. For example, the second comparator CP 2  outputs a result value made by comparing the output value of the second amplifier AMP2 with the triangular wave outputted from the second oscillator OSC 2 . 
     The second PWM generator PG 2  receives the output value of the second comparator CP 2  and outputs, to the second converter  142 , the second PWM signal PWM2 having a duty made by reflecting the output value of the second comparator CP 2 . Therefore, the second transistor T 2  of the second converter  142  performs an ON/OFF switching operation corresponding to the second PWM signal PWM2, such that the second converter  142  converts the boost voltage Vbst into the driving voltage Vout in accordance with the duty of the second PWM signal PWM2. 
       FIG.  4    is a block diagram of the reference voltage calculator of the display device according to the embodiment of the present disclosure. 
       FIG.  5    is a circuit diagram of a first reference voltage output part of the display device according to the embodiment of the present disclosure. 
     Referring to  FIGS.  4  and  5   , the reference voltage calculator  145  includes a 1-1 reference voltage calculator  145 - 1 , a 1-2 reference voltage calculator  145 - 2 , and a first reference voltage output part  145 - 3 . 
     The 1-1 reference voltage calculator  145 - 1  receives the input voltage Vin and converts the input voltage Vin into a 1-1 reference voltage Vref1-1. The 1-1 reference voltage Vref1-1 means a minimum voltage that allows the first converter  141  to operate. 
     Specifically, the first PWM signal PWM1 having a duty Dmin equal to or larger than a predetermined duty needs to be inputted to operate the first converter  141 . The minimum duty of the first PWM signal PWM1 for operating the first converter  141  can be defined as a first duty Dmin. The first duty Dmin can be derived as a ratio between a minimum ON time of the first PWM signal PWM1 and a switching cycle of the first PWM signal PWM1. 
     For example, the first duty Dmin can be expressed as Equation 1 below. 
         D min= T min_ on /Tpwm1  [Equation 1]
 
     In the above, Tmin_on represents the minimum ON time of the first PWM signal PWM1, and Tpwm1 represents the switching cycle of the first PWM signal PWM1. 
     Further, a relationship formula of the input voltage Vin and the boost voltage Vbst, which are the input and output voltages of the first converter  141 , can be expressed as Equation 2. 
       Vbst/ V in=1/(1− D min)  [Equation 2]
 
     Therefore, the boost voltage Vbst outputted from the first converter  141  is expressed as Vin/(1-Dmin). 
     Meanwhile, the distributed boost voltage (R2/(R1+R2)*Vbst) can be applied to the inverting terminal of the first amplifier AMP1. The 1-1 reference voltage Vref1-1, which is any one of the first reference voltages Vref1, can be applied to the non-inverting terminal of the first amplifier AMP1. The voltage at the inverting terminal of the first amplifier AMP1 and the voltage at the non-inverting terminal of the first amplifier AMP1 are equal to each other. For example, the 1-1 reference voltage Vref1-1 and the distributed boost voltage (R2/(R1+R2)*Vbst) are equal to each other. 
     Therefore, the 1-1 reference voltage Vref1-1 for operating the first converter  141  can be derived as R2/(R1+R2)* Vin/(1−Dmin) by using Equation 2. 
     For example, the 1-1 reference voltage calculator  145 - 1  can receive the input voltage Vin and set the 1-1 reference voltage Vref1-1 to R2/(R1+R2)* Vin/(1-Dmin). 
     The 1-2 reference voltage calculator  145 - 2  receives the driving voltage Vout and converts the driving voltage Vout into a 1-2 reference voltage Vref1-2. The 1-2 reference voltage Vref1-2 means a minimum voltage that allows the second converter  142  to operate. 
     Specifically, the second PWM signal PWM2 having a duty equal to or smaller than a predetermined duty Dmax needs to be inputted to operate the second converter  142 . The maximum duty of the second PWM signal PWM2 for operating the second converter  142  can be defined as a second duty Dmax. The second duty Dmax can be derived as a ratio between a minimum OFF time of the second PWM signal PWM2 and a switching cycle of the second PWM signal PWM2. 
     For example, the second duty Dmax can be expressed as Equation 3 below. 
         D max=1−( T min_ off /Tpwm2)  [Equation 3]
 
     In the above, Tmin_off represents the minimum OFF time of the second PWM signal PWM2, and Tpwm2 represents the switching cycle of the second PWM signal PWM2. 
     Further, a relationship formula of the boost voltage Vbst and the driving voltage Vout, which are the input and output voltages of the second converter  142 , can be expressed as Equation 4. 
         V out/Vbst= D max  [Equation 4]
 
     Therefore, the boost voltage Vbst inputted from the second converter (boost converter)  142  can be expressed as Vout/Dmax. 
     Meanwhile, the distributed boost voltage (R2/(R1+R2)*Vbst) can be applied to the inverting terminal of the first amplifier AMP1. The 1-2 reference voltage Vref1-2, which is any one of the first reference voltages Vref1, can be applied to the non-inverting terminal of the first amplifier AMP1. The voltage at the inverting terminal of the first amplifier AMP1 and the voltage at the non-inverting terminal of the first amplifier AMP1 are equal to each other. For example, the 1-2 reference voltage Vref1-2 and the distributed boost voltage (R2/(R1+R2)*Vbst) are equal to each other. 
     Therefore, the 1-2 reference voltage Vref1-2 for operating the second converter  142  can be derived as R2/(R1+R2)* Vout/Dmax by using Equation 4. 
     For example, the 1-2 reference voltage calculator  145 - 2  can receive the driving voltage Vout and set the 1-2 reference voltage Vref1-2 to R2/(R1+R2)* Vout/Dmax. 
     The first reference voltage output part  145 - 3  outputs a larger value between the 1-1 reference voltage Vref1-1 and the 1-2 reference voltage Vref1-2, as the first reference voltage Vref1. As described above, the 1-1 reference voltage calculator  145 - 1  derives the 1-1 reference voltage Vref1-1 that is a minimum voltage for operating the first converter  141 . The 1-2 reference voltage calculator  145 - 2  derives the 1-2 reference voltage Vref1-2 that is a minimum voltage for operating the second converter  142 . Further, both the first converter  141  and the second converter  142  need to operate to operate the power supplier  140 . 
     Therefore, the first reference voltage output part  145 - 3  outputs a larger value between the 1-1 reference voltage Vref1-1 and the 1-2 reference voltage Vref1-2, as the first reference voltage Vref1, in order to operate both the first converter  141  and the second converter  142 . 
     The first reference voltage output part  145 - 3  includes a multiplexer MUX and a comparator that receive the 1-1 reference voltage Vref1-1 and the 1-2 reference voltage Vref1-2. 
     The comparator compares the 1-1 reference voltage Vref1-1 and the 1-2 reference voltage Vref1-2 and outputs a comparison result value to the multiplexer MUX. 
     Further, depending on the result value of the comparator, the multiplexer MUX outputs a voltage having higher electric potential between the 1-1 reference voltage Vref1-1 and the 1-2 reference voltage Vref1-2, as the first reference voltage Vref1. 
       FIG.  6    is a voltage waveform diagram of the display device according to the embodiment of the present disclosure. 
     As illustrated in  FIG.  6   , the input voltage Vin can sequentially increase over time. Specifically, the external system connected to the power supplier  140  can be modified in various forms such as a power battery and a power adapter. Therefore, the input voltage Vin can also vary. For example, the input voltage Vin can be 8.5 V at a point in time t0 and 12.1 V at a point in time t1 and can increase up to 13.7 V. 
     Further, the driving voltage Vout required to operate the display device  100  is fixed to a predetermined voltage. For example, the driving voltage Vout can be fixed to 13 V at all points in time. 
     Therefore, the 1-1 reference voltage calculator  145 - 1  can set the 1-1 reference voltage Vref1-1 to R2/(R1+R2)* Vin/(1−Dmin) by using the variable input voltage Vin. For example, the input voltage Vin is linearly proportional to the time, such that the 1-1 reference voltage Vref1-1 can also be linearly proportional to the time. 
     Further, the 1-2 reference voltage calculator  145 - 2  can set the 1-2 reference voltage Vref1-2 to R2/(R1+R2)* Vout/Dmax by using the fixed driving voltage Vout. For example, because the driving voltage Vout is constantly fixed, the 1-2 reference voltage Vref1-2 can also be constantly fixed. 
     In a first time section (section t0 to t1), the fixed 1-2 reference voltage Vref1-2 can be higher than the variable 1-1 reference voltage Vref1-1. Therefore, the first reference voltage output part  145 - 3  can output the fixed 1-2 reference voltage Vref1- 2 , as the first reference voltage Vref1, to the first feedback unit  143 , thereby outputting the fixed boost voltage Vbst. For example, in  FIG.  6   , in the first time section (section t0 to t1), the boost voltage Vbst can be fixed to 13.44 V. 
     Further, in a second time section (section after t1), the variable 1-1 reference voltage Vref1-1 can be higher than the fixed 1-2 reference voltage Vref1-2. Therefore, the first reference voltage output part  145 - 3  can output the variable 1-1 reference voltage Vref1-1, as the first reference voltage Vref1, to the first feedback unit  143 , thereby outputting the variable boost voltage Vbst. For example, in  FIG.  6   , in the second time section (section after t1), the boost voltage Vbst can linearly increase from 13.44 V to 15.2 V. 
     In the related art, the boost voltage Vbst is fixed to a predetermined voltage. Specifically, even in a case in which the input voltage inputted to the first converter is 12 V or 20 V, the boost voltage is raised to 24 V and outputted. Further, the boost voltage of 24 V inputted to the second converter is lowered to 13 V, which is the driving voltage, and outputted. 
     For example, the efficiency of the first converter according to the input and output voltages and currents in the case in which the input voltage is 12 V or 20 V in the display device in the related art is shown in Table 1. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Boost 
                   
                   
                   
                   
                   
               
               
                 Converter 
                 vin (V) 
                 Iin (A) 
                 Vout (V) 
                 Iout (A) 
                 Efficiency (%) 
               
               
                   
               
             
            
               
                 12 V 
                 12.09 
                 0.354 
                 23.21 
                 0.178 
                 96.53073 
               
               
                 20 V 
                 20.14 
                 0.215 
                 23.22 
                 0.177 
                 94.91559 
               
               
                   
               
            
           
         
       
     
     Further, the efficiency of the second converter according to the input and output voltages and currents in the case in which the input voltage is 12 V or 20 V in the display device in the related art is shown in Table 2. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Buck 
                   
                   
                   
                   
                   
               
               
                 Converter 
                 vin (V) 
                 Iin (A) 
                 Vout (V) 
                 Iout (A) 
                 Efficiency (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 12 V 
                 23.21 
                 0.178 
                 13.2 
                 0.26 
                 83.07152 
               
               
                 20 V 
                 23.22 
                 0.177 
                 13.19 
                 0.26 
                 83.44161 
               
               
                   
               
            
           
         
       
     
     When the input voltage is 12 V in the display device in the related art, the final efficiency of the power supplier is 80.19% (=96.53073%×83.071525). When the input voltage Vin is 20 V, the final efficiency of the power supplier is 79.20% (=94.91559×83.44161). 
     In contrast, in the case of the display device according to the embodiment of the present disclosure, the boost voltage Vbst can vary for each time section. For example, as illustrated in  FIG.  6   , when the input voltage Vin inputted to the first converter  141  is 8.5 V to 12.1 V (in the case of the first time section), the boost voltage Vbst can be fixed to 13.44 V. When the input voltage Vin inputted to the first converter  141  is 12.1 V or higher (in the case of the second time section), the boost voltage Vbst can linearly increase. Further, the boost voltage Vbst inputted to the second converter  142  is lowered to 13 V, which is the driving voltage Vout, and outputted. 
     For example, the efficiency of the first converter  141  according to the input and output voltages and currents when the input voltage Vin is 12 V or 20 V in the display device  100  according to the embodiment of the present disclosure is shown in Table 3. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Boost 
                   
                   
                   
                   
                   
               
               
                 Converter 
                 vin (V) 
                 Iin (A) 
                 Vout (V) 
                 Iout (A) 
                 Efficiency (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 12 V 
                 12.19 
                 0.333 
                 14.8 
                 0.26 
                 94.79537 
               
               
                 20 V 
                 20.2 
                 0.205 
                 19.92 
                 0.205 
                 98.61386 
               
               
                   
               
            
           
         
       
     
     Further, the efficiency of the second converter  142  according to the input and output voltages and currents when the input voltage is 12 V or 20 V in the display device  100  according to the embodiment of the present disclosure is shown in Table 4. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Buck 
                   
                   
                   
                   
                   
               
               
                 Converter 
                 vin (V) 
                 Iin (A) 
                 Vout (V) 
                 Iout (A) 
                 Efficiency (%) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 12 V 
                 14.8 
                 0.26 
                 13.21 
                 0.262 
                 89.94335 
               
               
                 20 V 
                 19.92 
                 0.205 
                 13.21 
                 0.261 
                 84.43065 
               
               
                   
               
            
           
         
       
     
     In the display device  100  according to the embodiment of the present disclosure, the final efficiency of power supplier  140  is 85.26% (=94.79537%×89.94335%) when the input voltage Vin is 12 V. When the input voltage Vin is 20 V, the final efficiency of the power supplier  140  is 83.26% (=98.61386%×84.43065%). 
     For example, it can be seen that when the input voltage Vin is 12 V, the final efficiency of the power supplier  140  of the display device  100  according to the embodiment of the present disclosure increases by 5.07% in comparison with the display device in the related art. It can be seen that the final efficiency of the power supplier  140  increases by 5.07% when the input voltage Vin is 20 V. 
     For example, according to the display device according to the embodiment of the present disclosure, the efficiency of the first converter can be improved by reducing the input/output voltage difference of the first converter by changing the boost voltage. Further, the efficiency of the second converter can be improved by reducing the input/output voltage difference of the second converter. Therefore, the display device according to the embodiment of the present disclosure can improve the final efficiency of the power supplier. 
     Hereinafter, a power drive part  240  of a display device according to another embodiment of the present disclosure will be described. The power drive part  240  of the display device according to the embodiment of the present disclosure differs from the power drive parts  140  and  340  of the display device according to the other embodiments of the present disclosure only in terms of a mode controller  246 . Therefore, the difference will be specifically described. 
       FIG.  7    is a block diagram of a power supplier of a display device according to another embodiment of the present disclosure. 
       FIG.  8    is a circuit diagram of the power supplier of the display device according to another embodiment of the present disclosure. 
     Referring to  FIG.  7   , the power supplier  240  includes a first converter (boost converter)  241 , a second converter (buck converter)  242 , a first feedback unit (boost feedback)  243 , a second feedback unit (buck feedback)  244 , a reference voltage calculator (Vref calculator)  245 , and the mode controller  246 . 
     The mode controller  246  receives the 1-2 reference voltage Vref1-2 and the input voltage Vin and determines whether to operate in a normal mode or a bypass mode. 
     The configuration in which the first converter  241  operates in the normal mode means that the first transistor T 1  is repeatedly switched in response to the first PWM signal PWM1 outputted from the first feedback unit  243 , such that the first converter  241  outputs the boost voltage Vbst as (R1+R2)/R1*Vref1, as described above with reference to the display device according to the above-mentioned embodiment of the present disclosure. 
     For example, in the normal mode, the first converter  241  is controlled by the first feedback unit  243  and outputs the boost voltage Vbst in proportion to the first reference voltage Vref1. 
     Further, the configuration in which the first converter  241  operates in the bypass mode means that the first transistor T 1  is turned off, and the first converter  241  bypasses the input voltage Vin through the first inductor L 1  and the first diode D 1  and outputs the boost voltage Vbst as the input voltage Vin. However, because the boost voltage Vbst is outputted through the first diode D 1 , a voltage difference can occur by a Schottky diode voltage between the input voltage Vin and the boost voltage Vbst. 
     For example, in the bypass mode, the first converter  241  bypasses the input voltage Vin and outputs the boost voltage Vbst. 
     Specifically, referring to  FIG.  8   , the mode controller  246  includes a third comparator CP 3 , an AND gate AND, a third amplifier AMP3, and a plurality of resistors R6 and R7. 
     The third amplifier AMP3 amplifies the 1-2 reference voltage Vref1-2 to a mode voltage Vm. Specifically, the third comparator CP 3  and the sixth resistor R6 and the seventh resistor R7, which are connected in series in series, are connected to an output port of the third amplifier AMP3. An inverting terminal of the third amplifier AMP3 is connected between the sixth resistor R6 and the seventh resistor R7. A non-inverting terminal of the third amplifier AMP3 is connected to the reference voltage calculator  245 . Therefore, the third amplifier AMP3 receives the 1-2 reference voltage Vref1-2, amplifies the mode voltage Vm to the (R6+R7)/R7 *Vref1-2, and outputs the mode voltage. 
     The third comparator CP 3  can compare the input voltage Vin and the mode voltage Vm and outputs a comparison value. The input voltage Vin is applied to the inverting terminal of the third comparator CP 3 . The mode voltage Vm is applied to the non-inverting terminal of the third comparator CP 3 . 
     When the input voltage Vin is lower than the mode voltage Vm, the comparison signal at an ON level (or high level) is outputted to the AND gate AND. When the input voltage Vin is higher than the mode voltage Vm, the comparison signal at an OFF level (or low level) is outputted to the AND gate AND. 
     Further, the AND gate AND can receive the comparison signal from the third comparator and the first PWM signal PWM1 from the first feedback unit  243  and control the first transistor T 1  of the first converter  241 . 
     Specifically, when the comparison signal at the ON level is applied to the AND gate AND, a control signal CS identical to the first PWM signal PWM1 is outputted, such that the first transistor T 1  is periodically switched. Therefore, the first transistor T 1  is repeatedly switched in response to the control signal CS identical to the first PWM signal PWM1, such that the first converter  241  can output the boost voltage Vbst as (R1+R2)/R1*Vref1. 
     For example, when the comparison signal at the ON level is applied to the AND gate AND, the first converter  241  operates in the normal mode. 
     Further, when the comparison signal at the OFF level is applied to the AND gate AND, the control signal CS at the OFF level (or low level) is outputted, such that the first transistor T 1  is turned off. Therefore, the first converter  241  can output the input voltage Vin without change through the first inductor L 1  and the first diode D 1 , thereby outputting the boost voltage Vbst as the input voltage Vin. However, because the boost voltage Vbst is outputted through the first diode D 1 , a voltage difference can occur by a Schottky diode voltage between the input voltage Vin and the boost voltage Vbst. 
     When the comparison signal at the OFF level is applied to the AND gate AND, the first converter  241  operates in the bypass mode. 
       FIG.  9    is a voltage waveform diagram of the display device according to another embodiment of the present disclosure. 
     In the first time section (section t0 to t1) and the second time section (section t1 to t2), the input voltage Vin can be lower than the mode voltage Vm. Therefore, the comparison signal at the ON level is applied to the AND gate AND, such that the normal mode in which the first converter  241  is controlled by the first feedback unit  243  can be implemented. 
     Therefore, referring to  FIG.  6   , in the embodiment of the present disclosure described above, the 1-2 reference voltage Vref1-2 fixed in the first time section (section t0 to t1) is outputted, as the first reference voltage Vref1, to the first feedback unit  243 , such that the fixed boost voltage Vbst can be outputted. For example, in the first time section (section t0 to t1), the boost voltage Vbst can be fixed to 13.44 V. Further, in the second time section (section t1 to t2), the variable 1-1 reference voltage Vref1-1, as the first reference voltage Vref1, can be outputted to the first feedback unit  243 , such that the variable boost voltage Vbst can be outputted. For example, in  FIG.  9   , in the second time section (section t1 to t2), the boost voltage Vbst can linearly increase from 13.44 V to 15.2 V. 
     In a third time section (section after t2), the input voltage Vin can be higher than the mode voltage Vm. Therefore, the comparison signal at the OFF level is applied to the AND gate AND, such that the bypass mode in which the first converter  241  outputs the input voltage Vin through the first diode D 1  can be implemented. 
     In the third time section (section after t2), the input voltage Vin can be outputted as the boost voltage Vbst through the first diode D 1 . Therefore, as illustrated in  FIG.  9   , in the third time section (section after t2), the boost voltage Vbst can correspond to the input voltage Vin. However, because the boost voltage Vbst is outputted through the first diode D 1 , there can occur a voltage difference by a Schottky diode voltage of 0.26 V between the input voltage Vin of 13.7 V and the boost voltage Vbst of 13.44 V based on the point in time t2. 
     In the display device in the related art, the normal operation in which the transistor is repeatedly switched and outputs the boost voltage in response to the PWM signal is continuously performed even though the input voltage increases. For this reason, a ripple of the driving voltage can occur because of the PWM signal. 
     However, according to the display device according to another embodiment of the present disclosure, when the input voltage increases, the transistor is not switched in response to the PWM signal, but the input voltage is bypassed by the boost voltage. Therefore, in the display device according to another embodiment of the present disclosure, the input voltage is bypassed by the boost voltage, such that no ripple occurs. 
     Therefore, the driving voltage of the display device according to another embodiment of the present disclosure is not affected by the ripple, thereby minimizing the power consumption caused by the ripple. 
     Hereinafter, a power drive part  340  of a display device according to still another embodiment of the present disclosure will be described. The power drive part  340  of the display device according to the embodiment of the present disclosure differs from the power drive parts  140  and  240  of the display device according to the above-mentioned embodiments of the present disclosure only in terms of a feedback voltage calculator  345  and a first feedback unit  343 . Therefore, the difference will be specifically described. 
       FIG.  10    is a block diagram of the power supplier of the display device according to still another embodiment of the present disclosure. 
     Referring to  FIG.  10   , the power supplier  340  includes a first converter (boost converter)  341 , a second converter (buck converter)  342 , a first feedback unit (boost feedback)  343 , a second feedback unit (buck feedback)  344 , and a feedback voltage calculator (Vfb calculator)  345 . 
     The first converter  341  raises an input voltage Vin, which is supplied from the external system to a boost voltage Vbst. For example, the first converter  341  can be a boost converter or a step-up converter that converts the input voltage Vin into the boost voltage Vbst by raising the input voltage Vin. 
     The second converter  342  lowers the raised boost voltage Vbst to a driving voltage Vout required to operate the display device  100 . For example, the second converter  342  can be a buck converter or a step-down converter that converts the boost voltage Vbst into the driving voltage Vout by lowering the boost voltage Vbst. 
     The first feedback unit  343  controls the first converter  341  so that the first converter  341  can output the constant boost voltage Vbst. For example, the first feedback unit  343  generates a first PWM signal PWM1 and outputs the first PWM signal PWM1 to the first converter  341  so that the boost voltage Vbst can be maintained at a predetermined level in proportion to the first reference voltage. 
     The second feedback unit  344  controls the second converter  342  so that the second converter  342  can maintain the driving voltage Vout. For example, the second feedback unit  344  generates a second PWM signal PWM2 and outputs the second PWM signal PWM2 to the second converter  342  so that the driving voltage Vout can be maintained at a predetermined level in accordance with a second reference voltage. 
     The feedback voltage calculator  345  calculates a feedback voltage Vfb and outputs the feedback voltage Vfb to the first feedback unit  343  so that the power supplier  340  can operate with maximum efficiency. For example, the feedback voltage calculator  345  receives the input voltage Vin and the driving voltage Vout, calculates the feedback voltage Vfb in accordance with the input voltage Vin and the driving voltage Vout, and outputs the feedback voltage Vfb to the first feedback unit  343 . 
     Hereinafter, a specific circuit configuration will be described with reference to  FIG.  11   , focusing on the first feedback unit  343  of the display device according to still another embodiment of the present disclosure. 
       FIG.  11    is a circuit diagram of a power supplier of a display device according to still another embodiment of the present disclosure. 
     Referring to  FIG.  11   , the first feedback unit  343  includes a plurality of resistors R1, R2, R3, and R8, a third capacitor C 3 , a first amplifier AMP1, a first oscillator OSC  1 , a first comparator CP 1 , and a first PWM generator PG 1 . 
     The first resistor R1 and the second resistor R2 are connected in series. The first resistor R1 and the second resistor R2, which are connected in series, are connected between an output port of the first converter  341  and a grounding terminal. Therefore, the first resistor R1 and the second resistor R2, which are connected in series, serve as voltage distributors that distribute the boost voltage Vbst. Therefore, the boost voltage Vbst distributed between the first resistor R1 and the second resistor R2 can be expressed as R2/(R1+R2)*Vbst. 
     Further, in the display device according to still another embodiment of the present disclosure, the inverting terminal of the first amplifier AMP1, which is a node between the first resistor R1 and the second resistor R2, can be connected to the feedback voltage calculator  345  through the eighth resistor R8, which is any one of the plurality of resistors. For example, one end of the eighth resistor R8 is connected to an inverting terminal of the first amplifier AMP1 that is a node between the first resistor R1 and the second resistor R2. The other end of the eighth resistor R8 is connected to the feedback voltage calculator  345 . 
     In other words, the inverting terminal of the first amplifier AMP1 is connected to the output port of the first converter  341  through another R1 of the plurality of resistors. The inverting terminal of the first amplifier AMP1 is connected to the grounding terminal through another R2 of plurality of resistors. 
     The first resistor R1 and the second resistor R2 can be connected to an inverting terminal of the first amplifier AMP1, and the distributed boost voltage (R2/(R1+R2)*Vbst) can be applied. Further, the first reference voltage Vref1 can be applied to the non-inverting terminal of the first amplifier AMP1. However, in the display device according to still another embodiment of the present disclosure, the first reference voltage Vref1 can be fixed without varying, unlike the display device according to the above-mentioned embodiment of the present disclosure. 
     Since the voltage at the inverting terminal of the first amplifier AMP1 and the voltage at the non-inverting terminal of the first amplifier AMP1 are equal to each other, the first reference voltage Vref1 can be the distributed boost voltage (R2/(R1+R2)*Vbst). Further, the third resistor R3 and the third capacitor C 3 , which are connected in series, are connected to an output terminal of the first amplifier AMP1, thereby stabilizing an output voltage of the first amplifier AMP1. For example, the first amplifier AMP1 derives a difference value between the distributed boost voltage (R2/(R1+R2)*Vbst) and the first reference voltage Vref1 and outputs an amplified value of the difference value. 
     Further, a first oscillator OSC 1  can be connected to the inverting terminal of the first comparator CP 1 , such that a triangular wave outputted from the first oscillator OSC 1  can be applied. Further, the first amplifier AMP1 can be connected to the non-inverting terminal of the first comparator CP 1 , such that an output value of the first amplifier AMP1 can be applied. Further, the first PWM generator PG 1  is connected to the output terminal of the first amplifier AMP1. For example, the first comparator CP 1  outputs, to the first PWM generator PG 1 , a result value made by comparing the output value of the first amplifier AMP1 with the triangular wave outputted from the first oscillator OSC 1 . 
     The first PWM generator PG 1  receives the output value of the first comparator CP 1  and outputs, to the first converter  341 , the first PWM signal PWM1 having a duty made by reflecting the output value of the first comparator CP 1 . Therefore, the first transistor T 1  of the first converter  341  performs an ON/OFF switching operation corresponding to the first PWM signal PWM1, such that the first converter  341  converts the input voltage Vin to the boost voltage Vbst in accordance with the duty of the first PWM signal PWM1. 
       FIG.  12    is a block diagram of a feedback voltage calculator of the display device according to still another embodiment of the present disclosure. 
       FIG.  13 A  is a circuit diagram of a first feedback voltage converter of the display device according to still another embodiment of the present disclosure. 
       FIG.  13 B  is a circuit diagram of a second feedback voltage converter of the display device according to still another embodiment of the present disclosure. 
       FIG.  14    is a circuit diagram of a feedback voltage output part of the display device according to still another embodiment of the present disclosure. 
     Referring to  FIG.  12   , the feedback voltage calculator  345  includes a first feedback voltage converter  345 - 1 , a second feedback voltage converter  345 - 2 , and a feedback voltage output part  345 - 3 . 
     The first feedback voltage converter  345 - 1  receives the input voltage Vin and converts the input voltage Vin into a first feedback voltage Vfb1. The first feedback voltage Vfb1 means a minimum voltage that allows the first converter  341  to operate. 
     Specifically, the first feedback voltage converter  345 - 1  lowers the input voltage Vin, distributes the lowered input voltage Vin, and outputs the first feedback voltage Vfb1. For example, the first feedback voltage converter  345 - 1  can lower the level of the input voltage Vin to the first reference voltage Vref1 or lower and output the first feedback voltage Vfb1. 
     As illustrated in  FIG.  13 A , the first feedback voltage converter  345 - 1  can include a plurality of diodes and a plurality of resistors Rd 1  and Rd 2  that are connected in series. 
     Therefore, the first feedback voltage converter  345 - 1  converts the input voltage Vin through the plurality of diodes, distributes the input voltage Vin lowered through the plurality of resistors Rd 1  and Rd 2 , and outputs the first feedback voltage Vfb1. Therefore, the first feedback voltage Vfb1 can be lower than the first reference voltage Vref1. 
     The second feedback voltage converter  345 - 2  receives the driving voltage Vout and converts the driving voltage Vout into a second feedback voltage Vfb2. The second feedback voltage Vfb2 means a minimum voltage that allows the second converter  342  to operate. 
     Specifically, the second feedback voltage converter  345 - 2  lowers the driving voltage Vout, distributes the lowered driving voltage Vout, and outputs the second feedback voltage Vfb2. For example, the second feedback voltage converter  345 - 2  can lower the level of the driving voltage Vout to the first reference voltage Vref1 or lower and output the second feedback voltage Vfb2. 
     As illustrated in  FIG.  13 B , the second feedback voltage converter  345 - 2  can include a plurality of diodes and a plurality of resistors Rd 3  and Rd 4  that are connected in series. 
     Therefore, the second feedback voltage converter  345 - 2  converts the driving voltage Vout through the plurality of diodes, distributes the driving voltage Vout lowered through the plurality of resistors Rd 3  and Rd 4 , and outputs the second feedback voltage Vfb2. Therefore, the second feedback voltage Vfb2 can be lower than the first reference voltage Vref1. 
     The feedback voltage output part  345 - 3  outputs a large value between the first feedback voltage Vfb1 and the second feedback voltage Vfb2, as the feedback voltage Vfb. As described above, the first feedback voltage converter  345 - 1  outputs the first feedback voltage Vfb1 that is a minimum voltage for operating the first converter  341 . The second feedback voltage converter  345 - 2  outputs the second feedback voltage Vfb2 that is a minimum voltage for operating the second converter  342 . Further, both the first converter  341  and the second converter  342  need to operate to operate the power supplier  340 . 
     Therefore, the feedback voltage output part  345 - 3  outputs a larger value between the first feedback voltage Vfb1 and the second feedback voltage Vfb2, as the feedback voltage Vfb, in order to operate both the first converter  341  and the second converter  342 . 
     Referring to  FIG.  14   , the feedback voltage output part  345 - 3  includes a multiplexer MUX and a comparator that receive the first feedback voltage Vfb1 and the second feedback voltage Vfb2. 
     The comparator compares the first feedback voltage Vfb1 and the second feedback voltage Vfb2 and outputs the comparison result value to the multiplexer MUX. 
     Further, depending on the result value of the comparator, the multiplexer MUX outputs a voltage having higher electric potential between the first feedback voltage Vfb1 and the second feedback voltage Vfb2, as the feedback voltage Vfb. 
     Meanwhile, referring to  FIG.  11   , because the voltage at the non-inverting terminal of the first amplifier AMP1 and the voltage at the inverting terminal of the first amplifier AMP1 are equal to each other, the first reference voltage Vref1 is applied to the non-inverting terminal of the first amplifier AMP1. 
     Therefore, a first current I1 flowing through the second resistor R2 can be expressed as Vref1/R2, and a second current I2 flowing through the eighth resistor R8 can be expressed as (Vref1-Vfb)/R8. Therefore, the current I (total) flowing through the first resistor R1 is a sum of the first current I1 and the second current  12  and thus be expressed as (Vref1/R2+(Vref1-Vfb)/R8). 
     Therefore, the boost voltage Vbst can be expressed as a sum of voltage applied to the first reference voltage Vref1 and the first resistor R1. For example, the boost voltage Vbst can be expressed as (Vref1+{Vref1/R2+(Vref1-Vfb)/R8}*R1). In summary, based on the boost voltage Vbst, the voltage can be expressed as (Vref1(1+R1/R2+R1/R8)−Vfb(R1/R8)). 
     For example, because the boost voltage Vbst varies depending on the feedback voltage Vfb, the boost voltage Vbst can be controlled by adjusting the feedback voltage Vfb. 
     In other words, according to the display device according to another embodiment of the present disclosure, the boost voltage Vbst can be controlled by adjusting the feedback voltage Vfb applied to the first feedback unit  343  that controls the first converter  341 . 
     According to the display device according to still another embodiment of the present disclosure, the efficiency of the first converter can be improved by reducing the input/output voltage difference of the first converter by changing the boost voltage. Further, the efficiency of the second converter can be improved by reducing the input/output voltage difference of the second converter. Therefore, the display device according to still another embodiment of the present disclosure can improve the final efficiency of the power supplier. 
     The exemplary embodiments of the present disclosure can also be described as follows: 
     According to an aspect of the present disclosure, a display device can include a display panel having a plurality of pixels disposed on a substrate, and a power supplier configured to supply a driving voltage to the display panel. The power supplier can include a first converter configured to receive an input voltage supplied from an external system and convert the input voltage into a boost voltage, a second converter configured to convert the boost voltage into the driving voltage, a first feedback unit configured to output a first PWM signal to the first converter so that the boost voltage is proportional to a first reference voltage, a second feedback unit configured to output a second PWM signal to the second converter so that the driving voltage is proportional to a second reference voltage, and a reference voltage calculator configured to receive the input voltage and the driving voltage and supply the first reference voltage to the first feedback unit. Therefore, it is possible to improve the power conversion efficiency of the power supplier. 
     The first converter can be a boost converter including a first inductor, a first diode, a first transistor, and a first capacitor, and the first transistor can perform a switching operation corresponding to the first PWM signal, such that the first converter can convert the input voltage into the boost voltage in accordance with a duty of the first PWM signal. 
     The first feedback unit can include a plurality of resistors, a first amplifier, and a first PWM generator, the plurality of resistors distributes the boost voltage, the distributed boost voltage can be applied to an inverting terminal of the first amplifier, the first reference voltage can be applied to a non-inverting terminal of the first amplifier, and the first PWM generator can output the first PWM signal so that the distributed boost voltage and the first reference voltage are equal to each other. 
     The second converter can be a buck converter including a second inductor, a second transistor, a third transistor, and a second capacitor, and the second transistor and the third transistor can perform switching operations corresponding to the second PWM signal, so that the second converter can convert the boost voltage into the driving voltage in accordance with a duty of the second PWM signal. 
     The second feedback unit can include a plurality of resistors, a second amplifier, and a second PWM generator, the plurality of resistors distributes the driving voltage, the distributed driving voltage can be applied to an inverting terminal of the second amplifier, the second reference voltage can be applied to an non-inverting terminal of the second amplifier, and the second PWM generator can output the second PWM signal so that the distributed driving voltage and the second reference voltage are equal to each other. 
     The reference voltage calculator can include a 1-1 reference voltage calculator, a 1-2 reference voltage calculator, and a first reference voltage output part, the 1-1 reference voltage calculator can calculate a 1-1 reference voltage based on the input voltage, the 1-2 reference voltage calculator can calculate a 1-2 reference voltage based on the driving voltage, and the first reference voltage output part can output, as the first reference voltage, a voltage at a higher level between the 1-1 reference voltage and the 1-2 reference voltage. 
     The 1-1 reference voltage can be a minimum voltage that allows the first converter to operate, and the 1-2 reference voltage can be a minimum voltage that allows the second converter to operate. 
     The input voltage can be variable, and the 1-1 reference voltage varies depending on the input voltage. 
     The driving voltage can be fixed, and the 1-2 reference voltage can be fixed depending on the driving voltage. 
     The first reference voltage output part can output the 1-2 reference voltage, as the first reference voltage, to the first feedback unit in a first time section, and the first reference voltage output part can output the 1-1 reference voltage, as the first reference voltage, to the first feedback unit in a second time section. 
     The display device of claim can further comprise a mode controller configured to receive the 1-2 reference voltage and the input voltage and determine whether the first converter can operate in a normal mode or a bypass mode, in the normal mode, the first converter can be controlled by the first feedback unit and can output the boost voltage in proportion to the first reference voltage, and in the bypass mode, the first converter bypasses the input voltage and can output the input voltage as the boost voltage. 
     The mode controller can include an amplifier, a comparator, and an AND gate, the amplifier amplifies the 1-2 reference voltage to a mode voltage, the comparator can compare the input voltage and the mode voltage, and the AND gate receives the first PWM signal and a comparison signal of the comparator and can output a control signal for controlling the first converter. 
     The input voltage can be applied to an inverting terminal of the comparator, and the mode voltage can be applied to a non-inverting terminal of the comparator. 
     The comparator can output a comparison signal at an ON level to the AND gate when the input voltage can be lower than the mode voltage, and the comparator can output a comparison signal at an OFF level to the AND gate when the input voltage can be higher than the mode voltage. 
     The AND gate can operate the first converter in the normal mode by outputting the control signal identical to the first PWM signal when the comparison signal at the ON level can be applied, and the AND gate can operate the first converter in the bypass mode by outputting the control signal at the OFF level when the comparison signal at the OFF level can be applied. 
     According to another aspect of the present disclosure, a display device can include a display panel having a plurality of pixels disposed on a substrate, and a power supplier configured to supply a driving voltage to the display panel. The power supplier can include a first converter configured to convert an input voltage, which is supplied from an external system, into a boost voltage, a second converter configured to convert the boost voltage into the driving voltage, a first feedback unit configured to control the first converter so that the first converter outputs the boost voltage, a second feedback unit configured to control the second converter so that the second converter outputs the driving voltage, and a feedback voltage calculator configured to calculate a feedback voltage from the input voltage and the driving voltage. The first feedback unit can include a plurality of resistors, a first amplifier, and a first PWM generator, in which a first reference voltage is applied to a non-inverting terminal of the first amplifier. Further, an inverting terminal of the first amplifier is connected to the feedback voltage calculator through any one of the plurality of resistors, and the first PWM generator outputs a first PWM signal to the first converter so that the boost voltage is proportional to the first reference voltage. Therefore, it is possible to improve the power conversion efficiency of the power supplier. 
     The first converter can comprise a first inductor, a first diode, a first transistor, and a first capacitor, and the first transistor can perform a switching operation corresponding to the first PWM signal, such that the first converter can convert the input voltage into the boost voltage in accordance with a duty of the first PWM signal. 
     The inverting terminal of the first amplifier can be connected to an output port of the first converter through another of the plurality of resistors, and the inverting terminal of the first amplifier can be connected to a grounding terminal through another of the plurality of resistors. 
     The feedback voltage calculator can include a first feedback voltage converter, a second feedback voltage converter, and a feedback voltage output part, the first feedback voltage converter can convert the input voltage into a first feedback voltage by lowering the input voltage to the first reference voltage or lower, the second feedback voltage converter can convert the driving voltage into a second feedback voltage by lowering the driving voltage to the first reference voltage or lower, and the feedback voltage output part can output, as the feedback voltage, a voltage at a higher level between the first feedback voltage and the second feedback voltage. 
     The first feedback voltage can be a minimum voltage that allows the first converter to operate, and the second feedback voltage can be a minimum voltage that allows the second converter to operate. 
     Although the exemplary embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the present disclosure is not limited thereto and can be embodied in many different forms without departing from the technical concept of the present disclosure. Therefore, the exemplary embodiments of the present disclosure are provided for illustrative purposes only but not intended to limit the technical concept of the present disclosure. The scope of the technical concept of the present disclosure is not limited thereto. 
     Therefore, it should be understood that the above-described exemplary embodiments are illustrative in all aspects and do not limit the present disclosure. The protective scope of the present disclosure should be construed based on the following claims, and all the technical concepts in the equivalent scope thereof should be construed as falling within the scope of the present disclosure.