Patent Publication Number: US-2023137522-A1

Title: Display system and method for driving display module

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation application, under 35 U.S.C. § 111(a), of international application No. PCT/KR2022/012141, filed on Aug. 12, 2022, which claims priority from Korean Patent Application No. 10-2021-0150394, filed on Nov. 4, 2021, the disclosures of which are hereby incorporated by reference in their entirety for all purposes as if fully set forth herein. 
    
    
     BACKGROUND 
     Field 
     The present disclosure relates to a display module that operates with electric power received in a wireless manner from the outside, and a display system including the same. More particularly, the disclosure relates to a display module capable of quickly recovering its screen display without restart up even though the power supply from the outside is temporarily interrupted, and such a display system including the same. 
     Description of Related Art 
     There is a need for a display module that can be variously utilized depending on various using purposes. With this demand, while most traditional televisions (TVs) have been used only for showing television programs, recently a single display module, which can be used as a television to show television programs, may also be used as a picture frame for digital art works, a photo album or a personal monitor in case where it is not used as a television. Such a need for a display module that can be adaptively utilized in accordance with various purposes and situations does not simply arise in relation to a living room TV, but is expanding to a variety of display modules with various sizes (e.g., personal display modules of compact size). In order to be adaptively utilized to meet various using purposes, the display module needs to be freely re-arranged (e.g., as tilted or pivoted at various angles) according to user&#39;s demands, rather than being fixedly kept in a certain arrangement. 
     SUMMARY 
     According to one aspect of the disclosure, provided is a display system comprising a display displaying a screen based on image information to be displayed, and a power supply configured to support the display and supply electric power to the display in a wireless manner, wherein when the display is spaced apart from the power supply by a predetermined distance or more, the display is configured to selectively operate in one of a power saving mode for lowering luminance of at least a portion of the screen and an ultra-power saving mode for turning OFF at least a portion of the screen while maintaining a turned-on state of the display module. 
     According to another aspect of the present disclosure, provided is a method for driving a display including a power supply unit and a light emitting unit, the method comprising displaying a screen by controlling light emission of the light emitting unit based on image information to be displayed, determining a decrease in a voltage of a current applied from the power supply unit, and in response to determining the decrease in the voltage, selectively entering either one of a power saving mode in which luminance of at least a portion of the light emitting unit is lowered or an ultra-power saving mode in which at least a portion of the light emitting unit is turned OFF while maintaining a turned-on state of the display. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIGS.  1 A,  1 B and  1 C  are perspective views respectively showing various using examples of a display system according to an embodiment of the disclosure. 
         FIG.  2    is a schematic block diagram showing a functional configuration of a display system according to an embodiment of the disclosure. 
         FIG.  3 A  is a diagram schematically illustrating a cross-section of a stand having a power transmission (TX) resonator according to an embodiment of the disclosure. 
         FIG.  3 B  is a graphic diagram conceptually illustrating a change in voltage received by a reception (RX) resonator of a display module depending on a distance from the stand illustrated in  FIG.  3 A . 
         FIG.  4    is a circuit diagram illustrating an exemplary circuit configuration of the display module corresponding to the stand of  FIG.  3 A  according to an embodiment of the disclosure. 
         FIGS.  5 A,  5 B and  5 C  are schematic circuit diagrams respectively showing a current flow generated in the display module and an operating state of a light emitting unit, depending upon a change in relative position between the display module shown in  FIG.  4    and the stand shown in  FIG.  3 A , according to an embodiment of the disclosure. 
         FIG.  6    illustrates a change in voltage and current in each part of the display module over time, in case that the display module is initially arranged to be supported by a support surface of the stand. 
         FIG.  7    illustrates a change in voltage and current in each part of the display module and a controlled status of a switch SW, as the display module is moved further away from the support surface of the stand. 
         FIG.  8    is a diagram illustrating an example of using the display module in which the display module is pivoted and re-arranged with respect to the stand, according to an embodiment of the disclosure. 
         FIG.  9 A  is a side view schematically illustrating a side of a stand and a display module disposed to be supported by the stand according to an embodiment of the disclosure. 
         FIG.  9 B  is a graphic diagram conceptually illustrating a change in voltage received by the display module depending on a distance from the stand illustrated in  FIG.  9 A . 
         FIG.  10    is a circuit diagram illustrating an exemplary circuit configuration of the display module according to an embodiment of the disclosure. 
         FIGS.  11 A and  11 B  are diagrams showing a current flow generating in the display module and an operating state of a light emitting unit, depending upon a change in position of the display module with respect to the stand, according to an embodiment of the disclosure. 
         FIG.  12    is a graph showing a change in voltage and current in each part of the display module, when the power supply between receiving electrodes of the display module and transmitting electrodes of the stand is interrupted. 
         FIG.  13    is a circuit diagram schematically illustrating the configuration of an exemplary display module with modification in a portion of an internal circuit of the display module shown in  FIG.  11 B , according to an embodiment of the disclosure. 
         FIG.  14    is a diagram illustrating an example of using the display module in which the display module is pivoted from its original position and re-arranged on the stand, according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. In the following description, specific details, such as detailed configurations and components, will be provided merely to help a general understanding of various embodiments of the disclosure. In connection with the description of the drawings, the same or similar reference numerals may be used for the same or similar components. In addition, throughout the drawings and their related descriptions, descriptions of well-known functions and configurations may be omitted for clarity and conciseness. 
     The display module according to various embodiments of the disclosure can be disposed and used on a stand configured to support the display module at various angles and supply power to the display module in a wireless manner. Thus, the display module can be freely re-arranged (e.g., tilted or pivoted) with respect to the stand without any physical restrictions by a wired power cable, depending upon various using purposes. 
     The display module according to various embodiments of the disclosure can operate in either a power saving mode or an ultra-power saving mode with a small amount of power charged in a power storage element in the display module, without having to equip a complicated charge/discharge battery circuit, even though the power supply from the stand is temporarily interrupted while the display module is rearranged with respect to the stand. Therefore, the display module can maintain its turned-on state continuously only with minimal power consumption so as to quickly restore the screen display without restart-up when the power supply gets back to normal subsequent to completion of rearrangement of the display module. 
     In case where free tilting or pivoting of a display module is implemented with a mechanical configuration built into the display module itself, there arises a problem that the display module increases in its weight and thickness and its manufacturing cost can increase. In case where the display module, which is being supplied via a wired power cable attached thereto, is rearranged by tilting or pivoting, the user&#39;s convenience and aesthetic impression in use may be affected by the power cable. In addition, in case where the power supply to the display module is interrupted while the display module is being rearranged and therefore, a restart-up of the display module is required after the power supply is resumed, the user experience may be significantly impaired. 
     One aspect of the present disclosure is to provide a display module that can be freely tilted or pivoted with a user&#39;s simple operation, without any additional mechanical configuration in the display module itself, and a display system including the same. 
     Another aspect of the present disclosure is to provide a display module configured to, even if the power supply to the display module from the outside is temporarily interrupted while the display module is re-arranged, maintain the turned-on state of the display module continuously so as to quickly restore its screen display without restart-up thereof upon completion of the rearrangement, and a display system including the same. 
       FIGS.  1 A,  1 B and  1 C  are perspective views schematically showing various using examples of a display system  100  according to an embodiment of the disclosure. As illustrated, the display system  100  may include a display module  110  for displaying a screen, and a stand  120  configured to support the display module  110 . 
     According to various embodiments of the disclosure, the display module  110  may be an image or video display device configured to display, on a screen, broadcast or various image signals received from the outside in a wired or wireless manner or obtained in a predetermined manner. According to various embodiments of the disclosure, the display module  110  may be an image display device that can be utilized for various using purposes, including e.g., television (TV), smart TV, IP TV, smartphone, tablet PC, personal monitor, digital picture frame, and/or photo album, and the present disclosure is not limited in relation to a specific use of the display module. For example, according to some embodiments of the present disclosure, the display module  110  may operate as a TV to receive and display a broadcast signal while the user is watching TV, and operate to display a certain still image or a moving picture (e.g., a digital picture, a photo, or other various graphic displays) when the user stops watching TV. According to various embodiments of the disclosure, the display module  110  may be a display module of various types such as e.g., LED, OLED, Micro-LED, LCD, Mini-LED, Quantum-dot LED and so on, and the present disclosure is not limited to any specific type of display module. 
     According to an embodiment of the disclosure, the display module  110  may be of a rectangular shape having a longer side and a shorter side S of different lengths as shown in  FIG.  1 A , and the present disclosure is not limited thereto. In this context,  FIG.  1 A  illustrates an arrangement in which the display module  110  is used in a landscape mode where the longer side is horizontally arranged on the stand  120 , and  FIG.  1 B  illustrates another arrangement in which the display module  110  is pivotally rotated from that of  FIG.  1 A  and used in a portrait mode where the longer side is vertically arranged on the stand  120 . 
     According to an embodiment of the disclosure, the stand  120  may include a bottom surface  121  of a rectangular shape that can be placed in contact with the ground or floor, and support surfaces  122   a  and  122   b  extending upward from the bottom surface  121 , the support surfaces  122   a  and  122   b  each being configured to support a rear side  112  of the display module  110 . According to an embodiment of the disclosure, each of the support surfaces  122   a  and  122   b  on both sides of the stand  120  may include a flat surface extending upwardly from a predetermined position of the bottom surface  121  with a different angle with respect to the bottom surface  121 . For example, according to an embodiment of the disclosure, one support surface  122   a  of both support surfaces  122   a  and  122   b  may include an inclined surface extending upwards from one longer edge of the bottom surface  121  of a rectangular shape at a certain acute angle with respect to the bottom surface  121 , as shown in  FIGS.  1 A and  1 B . Similarly, according to an embodiment of the disclosure, the other support surface  122   b  of both support surfaces  122   a  and  122   b  may include a vertical plane extending upwards from the other longer edge of the bottom surface  121  of a rectangular shape perpendicularly to the bottom surface  121 . Although not explicitly specified in the drawings, according to an embodiment of the disclosure, the stand  120  may further include a mechanical configuration that can be coupled to the display module  110  on each of both sides of the support surfaces  122   a  and  122   b.    
     Referring to  FIGS.  1 A,  1 B and  1 C , the bottom surface  121  and both of the support surfaces  122   a  and  122   b  of the stand  120  are shown as forming a recumbent right-angled triangular prism shape, but the present disclosure is not limited thereto. Further,  FIGS.  1 A,  1 B and  1 C  illustrate that the stand  120  has two support surfaces  122   a  and  122   b , but the present disclosure is not limited thereto. According to another embodiment of the disclosure, the stand  120  may have various different shapes capable of providing one or more support surfaces for the display module  110 . 
     According to an embodiment of the disclosure, the stand  120  may include a protrusion  123  in front of the support surface  122   b  perpendicular to the bottom surface  121 . The protrusion  123  may serve as a safety means against overturning of the display module  110  due to its own load, when the display module  110  is coupled to the support surface  122   b  to be vertically arranged on the stand  120  in use. 
     According to an embodiment of the disclosure, the display module  110  may be coupled to either one of the support surfaces  122   a  and  122   b  on both sides of the stand  120  depending on a user&#39;s intended purpose. According to an embodiment of the disclosure, as shown in  FIGS.  1 A to  1 C , the support surfaces  122   a  and  122   b  on both sides of the stand  120  may be configure to have different angles with respect to the bottom surface  121 . In this case, according to which of the support surfaces is coupled to and support the display module  110 , the display module  110  may be used in a respective different arrangement where the display module is tilted at a respective different angle from a viewing direction. For example, in  FIGS.  1 A and  1 B  is shown an arrangement in which the display module  110  is supported by the vertical support surface  122   b  and is vertically disposed with respect to the viewing direction in use. Further, in  FIG.  1 C  is shown an arrangement in which the display module  110  is supported by the inclined support surface  122   a  and is obliquely disposed with respect to the viewing direction. Further, according to an embodiment of the disclosure, the display module  110  may be used pivotally rotated in various angles to suit the purpose of use, while it is supported by each of the supporting surfaces  122   a  and  122   b . For example,  FIG.  1 A  illustrates that the display module  110  is supported by the vertical support surface  122   b  and used in landscape mode, and  FIG.  1 B  illustrates that the display module  110  is pivotally rotated from that of  FIG.  1 A  and used in portrait mode. 
     According to an embodiment of the disclosure, as shown above, the stand  120  may include a power plug  124  connected via cable. The stand  120  may be configured to receive an external input power through the power plug  124 . According to an embodiment of the disclosure, the power plug  124  may receive, for example, a common AC power from an electric outlet installed on a wall of a house. According to an embodiment of the disclosure, the power plug  124  may receive DC/AC power from various DC/AC current sources. According to one embodiment of the present disclosure, the stand  120  may operate to receive the power through the power plug  124  or in various other ways and supply the received power to the display module  110  in a wireless manner (e.g., in any of various ways using no power cable, inclusive of e.g., a non-contact wireless way or a way through contact between electrodes). Although not explicitly shown in the drawings disclosed herein, the stand  120  may further include a structure for power transmission to the display module  110  either inside or outside thereof. 
       FIG.  2    is a block diagram schematically illustrating a functional configuration of a display system  200  according to an embodiment of the disclosure. As shown in  FIG.  2   , the display system  200  may include a display module  210  (e.g., the display module  110  of  FIG.  1   ) and a stand  220  (e.g., the stand  120  of  FIG.  1   ). According to various embodiments of the disclosure, the display module  210  may include a power unit  212 , a power storage  214 , and a screen display unit  216 , as shown in  FIG.  2   . According to various embodiments of the disclosure, the stand  220  may include a power receiver  222 , a converter  224 , and a power transmitter  226 . 
     According to an embodiment of the disclosure, the power receiver  222  may receive input power coming into the stand  220 , for example, through the power plug  124  of  FIG.  1    (not shown in  FIG.  2   ), but the present disclosure is not limited thereto. According to an embodiment of the disclosure, the input power may be a common AC power or any input power received from various other types of DC/AC current sources. According to an embodiment of the disclosure, the power receiver  222  may, for example, receive an AC power and/or generate a predetermined DC voltage power through appropriate rectification, power factor compensation, and/or transformation processes as required. According to an embodiment of the disclosure, the power receiver  222  may receive a predetermined DC voltage power from an external adapter. 
     According to an embodiment of the disclosure, the converter  224  may convert the DC voltage power from the power receiver  222  into a predetermined high-frequency AC voltage power for wireless power transmission. For example, according to an embodiment of the disclosure, when the power transmitter  226  is configured to have a transmission (TX) resonator and perform a wireless power transmission via a magnetic induction by magnetic field generation, the converter  224  can generate a high frequency AC voltage power at a predetermined operating frequency corresponding to a resonant frequency of the transmission (TX) resonator. According to another embodiment of the disclosure, the converter  224  may convert the DC voltage power from the power receiver  222  into a predetermined DC voltage power, and the present disclosure is not limited to such a specific form. 
     According to an embodiment of the disclosure, the power transmitter  226  may include a configuration capable of transmitting power to the display module  220  in a wireless manner. For example, according to an embodiment of the disclosure, the power transmitter  226  may include a transmission (TX) resonator (not shown) configured to generate a magnetic field oscillating at a predetermined frequency based on an AC voltage signal applied from the converter  224 . According to an embodiment of the disclosure, the power transmitter  226  may include a transmission (TX) resonator configured to generate a magnetic field of the same shape and size in a direction toward each of the support surfaces of the stand  220  (e.g., in a direction toward the support surface  122   a  and another direction toward the support surface  122   b  in  FIG.  1   ) to transmit power toward each support surface, and a switch configured to select one of the support surfaces to which the power is transmitted, but the present disclosure is not limited thereto. According to another embodiment of the disclosure, the power transmitter  226  may include one or more contact electrodes (not shown) capable of providing a predetermined DC voltage power to the outside, that is, to the display module  210  by a point contact mode. In the present disclosure, the description is mainly focused on the circumstance in which the power transmitter  226  performs a wireless power transmission through magnetic induction or a power transmission via electrodes contact, but the present disclosure is not limited thereto. According to various embodiments of the disclosure, the power transmitter  226  may be configured to supply power to the display module  210  according to any type of wireless power transmission method. 
     According to various embodiments of the disclosure, the power unit  212  of the display module  210  may receive power supplied in a wireless manner from the power transmitter  226 . According to an embodiment of the disclosure, the power unit  212  may include a reception (RX) resonator (not shown) capable of receiving the power wirelessly through resonance with the transmission (TX) resonator of the power transmission unit  226 . According to an embodiment of the disclosure, when the reception (RX) resonator of the power unit  212  is configured to receive power wirelessly, the power unit  212  can operate to, for example, rectify the received AC voltage power to generate a predetermined DC voltage power. Further, according to another embodiment of the disclosure, the power unit  212  may include a contact electrode (not shown) capable of receiving a predetermined DC power through contact with the contact electrode of the power transmitter  226 , and the present disclosure is not limited to such a specific type of power unit. 
     According to various embodiments of the disclosure, the power storage  214  may include one or more power storage elements (not shown). According to various embodiments of the disclosure, although not specifically illustrated herein, the power storage  214  may include a charging current path and a discharging current path for the power storage element. According to various embodiments of the disclosure, when the power unit  212  receives power from the outside, for example, the power transmitter  226  of the stand  220 , the current applied from the power unit  212  via the charging current path can charge the power storage element (not shown) of the power storage  214 . According to various embodiments of the disclosure, the power storage element may be an element capable of storing a relatively small amount of electric power, such as a capacitor or a super capacitor, and may be distinguished from a charge/discharge battery system that requires a separate charge/discharge control circuit. According to various embodiments of the disclosure, for example, when the display module  210  is decoupled or detached from the stand  220  so that the power unit  212  receives no more power from the power transmitter  226 , a current from the power storage element of the power storage  214  may be supplied to the screen display unit  216  of the display module  210 , through the discharge current path. 
     According to various embodiments of the disclosure, the screen display unit  216  may include a plurality of light emitting devices (not shown) and a driving control unit. According to various embodiments of the disclosure, the screen display unit  216  operates to obtain and store image information to be displayed on the screen using a predetermined scheme, and controls the light emission and luminance of each light emitting device based on the image information, thereby displaying a screen corresponding to the image information. According to various embodiments of the disclosure, the screen display unit  216  may receive a driving current from the power unit  212  or the power storage  214 . According to various embodiments of the disclosure, for example, when the voltage of the driving current applied to the screen display unit  216  decreases (e.g., when the display module  210  is detached from the support surface of the stand  220  and thereby, the external power supply is reduced or stopped), the screen display unit  216  may operate to reduce the luminance of or turn OFF all or some of the plurality of light emitting devices, while maintaining a stored state of the image information for screen display. According to various embodiments of the disclosure, when the voltage of the driving current applied to the screen display unit  216  increases back again (e.g., when the display module  210  is disposed back again at a position on the support surface of the stand  220  so that the power supply is resumed), the screen display unit  216  can restore the luminance of the light emitting device based on the stored image information without restarting-up the display module  210 , thereby leading to quickly restoring the screen display. 
     Referring then to  FIGS.  3  to  8   , the configuration and operation of the display system  300 , which may correspond to the display system  100  of  FIG.  1   , according to an embodiment of the disclosure will be described. The display system  300  may include a stand  320  and a display module  310 . 
     First,  FIG.  3 A  is a diagram schematically showing a cross-section of the stand  320  having a power transmission (TX) resonator according to an embodiment of the disclosure, and  FIG.  3 B  is a diagram conceptually illustrating a change in voltage that can be received by a reception (RX) resonator of the display module  310  depending upon a distance spaced apart from the stand  320  shown in  FIG.  3 A . 
     According to an embodiment of the disclosure, as shown in  FIG.  3 A , the power transmission (TX) resonator  324  may be disposed in an inner space between the support surfaces  322   a  and  322   b  on both sides of the stand  320 . According to an embodiment of the disclosure, the transmission (TX) resonator  324  may be configured to form a resonant converter circuit with the reception (RX) resonator  424  of the display module  310 , which will be further described later with reference to  FIG.  4   , thereby operating to wirelessly transmit power to the reception (RX) resonator  424  through a magnetic induction. 
     According to an embodiment of the disclosure, the transmission (TX) resonator  324  may include a core  326 , and windings  328   a  and  328   b  disposed on both sides of the core  326 . According to an embodiment of the disclosure, the windings  328   a  and  328   b  may have a coil formed with a copper wire wound, but the present disclosure is not limited thereto. 
     According to an embodiment of the disclosure, as shown in  FIG.  3 A , in the transmission (TX) resonator  324 , the windings  328   a  and  328   b  may respectively by positioned on each side of the core  326  to face either side of the support surfaces  322   a  and  322   b  of the stand  320 , respectively. According to an embodiment of the disclosure, each of the windings  328   a  and  328   b  may be arranged to have the same angle (e.g., Θ 1 =Θ 2 ) and the same distance (e.g., h 1 =h 2 ) with respect to the respective opposing support surfaces  322   a  and  322   b . With this arrangement, the transmission (TX) resonator  324  may generate a magnetic field of the same resonant inductance (or leakage inductance) for both the support surfaces  322   a  and  322   b , and provide a consistent power transmission for the display module  310  supported by any of the support surfaces  322   a  and  322   b.    
     Referring to  FIG.  3 A , it is illustrated that only the transmission (TX) resonator  324  is disposed in the inner space of the stand  320 , but this is only to help the understanding of the disclosure. According to various embodiments of the disclosure, as described above with reference to  FIGS.  1  and  2   , the stand  320  may include various configurations for receiving power (e.g., common AC power) from the outside and then converting the received power appropriately, thereby enabling proximity wireless power transmission (e.g., a wireless power transmission based on magnetic induction) to the display module  310  through the transmission (TX) resonator  324 . 
     According to an embodiment of the disclosure, the display module  310  coupled to and supported on either one of the support surfaces  322   a  and  322   b  of the stand  320  may be detached from the corresponding support surface and then rearranged. For example, the display module  310  being coupled to the support surface  322   b  of the stand  320  in a landscape mode as shown in  FIG.  1 A  may be rearranged to pivot into a portrait mode as shown in  FIG.  1 B  or may be rearranged to be supported by another support surface  322   a  as shown in  FIG.  1 C . In such circumstances, the display module  310  may be moved more than a predetermined distance away from the support surface  322   b  and the transmission (TX) resonator  324  inside the stand  320  during occurrence of rearrangement. 
       FIG.  3 B  conceptually illustrates a change in voltage of power that can be transmitted from the stand  320  to the display module  310 , as the distance of the display module  310  from the stand  320  (or the transmission (TX) resonator  324  of the stand  320 ) changes. As shown, it can be seen that the voltage of the transmittable power is inversely proportional to an increase in the distance, when the distance of the display module  310  from the transmission (TX) resonator  324  is out of a predetermined range. 
       FIG.  4    is a diagram illustrating an exemplary circuit configuration of the display module  310  corresponding to the stand  320  of  FIG.  3 A , according to an embodiment of the disclosure. As illustrated, the display module  310  may include a power unit  312 , a power storage  314 , and a screen display unit  316 . 
     Referring to  FIG.  4   , the power unit  312  may include a reception (RX) resonator  424  and a rectifying section  422 . According to an embodiment of the disclosure, the reception (RX) resonator  424  may be configured to, for example, form a resonant circuit with the transmission (TX) resonator  324  of the stand  320  described in connection with  FIG.  3 A , and it may receive power wirelessly through magnetic induction. According to an embodiment of the disclosure, the reception (RX) resonator  424  may include a core  426  and a winding  428  disposed out of the core. According to an embodiment of the disclosure, the rectifying section  422  may rectify the power of the AC voltage received by the reception (RX) resonator  424  to convert it into the power of the DC voltage. 
     According to an embodiment of the disclosure, the power storage  314  may be connected to the power unit  312  in parallel with the screen display unit  316 , as shown in  FIG.  4   . According to an embodiment of the disclosure, the power storage  314  may include power storage elements, for example, a capacitor C, a charging diode D charge1  transferring the current from the power unit  312  to the capacitor C, and a resistor R limit1  connected between the capacitor C and the charging diode D charge1 . The capacitor C may cause rush incurrent to flow into the circuit, so the resistor R limit1  is disposed to prevent damage to the circuit due to such rush current. According to an embodiment of the disclosure, the power storage  314  may further include a switch SW connected to a point between the capacitor C and the resistor R limit1 , the switch providing a discharging path for the current discharged from the capacitor C. 
     According to an embodiment of the disclosure, as shown in  FIG.  4   , the screen display unit  316  may be connected to the power unit  312 . According to an embodiment of the disclosure, the screen display unit  316  may include a driver board  412 , a light emitting unit  414 , and an alarm unit  416 . 
     According to an embodiment of the disclosure, the driver board  412  is configured to control overall operations of the light emitting unit  414  and the alarm unit  416 . According to an embodiment of the disclosure, the driver board  412  may receive a current applied from the power unit  312  or a current discharged from the capacitor C, and provide an operating current to the light emitting unit  414  and the alarm unit  416 . According to an embodiment of the disclosure, the driver board  412  is configured to store, for example, broadcasting or other various image information received or acquired from the outside in a wired or wireless manner, and based on the image information, control the light emission and luminance of each light emitting device of the light emitting unit  414  (e.g., the operating current I LED1  for the light emitting unit  414 ), so as to display visual information, video or images on a display screen. According to an embodiment of the disclosure, the driver board  412  is configured to obtain measurements of a voltage V c  of the capacitor C and a voltage V in  of a driving current I powering  applied to the driver board  412 , and based on those voltage measurements, control each light emitting device of the light emitting unit  414  to operate in a power saving mode or an ultra-power saving mode. 
     According to an embodiment of the disclosure, the light emitting unit  414  may include a plurality of light emitting devices connected in series, for example, a plurality of light emitting diodes. Although it is illustrated in  FIG.  4    that the light emitting unit  414  includes one row of light emitting diodes connected in series, the present disclosure is not limited thereto. According to various embodiments of the disclosure, the light emitting unit  414  may include an array of various numbers of light emitting devices connected in various ways as required. 
     According to an embodiment of the disclosure,  FIG.  4    illustrates that the alarm unit  416  includes one lamp as shown therein, but the present disclosure is not limited thereto. According to some embodiments of the present disclosure, the alarm unit  416  may include various elements or devices to provide a visual and/or audible alarm indicating that the light emitting unit  414  is operating in the power saving mode or ultra-power saving mode. According to some embodiments of the present disclosure, the alarm unit  416  may include, for example, one or more lamps or beepers. Further, according to another embodiment of the disclosure, some of the light emitting elements constituting a part of the light emitting unit  414  (e.g., one or some of the plurality of light emitting diodes) may function as the alarm unit  416 , in place of a separate additional audio/visual indicating element. In this case, when the light emitting unit  414  is operating in the power saving mode or ultra-power saving mode, such an operating state of the display module  310  may be displayed via at least a portion of the display screen corresponding to the light emitting devices functioning as the alarm unit  416 . 
       FIGS.  5 A,  5 B and  5 C  are schematic circuit diagrams respectively showing a current flow generated in the display module  310  and an operating state of the light emitting unit  414 , depending upon a relative position between the display module  310  and the stand  320  according to an embodiment of the disclosure. More specifically, according to an embodiment of the disclosure,  FIG.  5 A  is a circuit diagram showing an initial current flow in the display module  310  and an operating state of the light emitting unit  414 , immediately after the display module  310  is coupled and disposed on the support surface of the stand  320 , that is, immediately after the reception (RX) resonator  424  of the power unit  312  is disposed in a proper position on the support surface that can receive a sufficient amount of power from the transmission (TX) resonator  324  of the stand  320 . According to an embodiment of the disclosure,  FIG.  5 B  is a circuit diagram showing the current flow within the display module  310  and the operating state of the light emitting unit  414 , in case where the display module  310  starts to detach from the original position in contact with the support surface of the stand  320  as shown in  FIG.  5 A  so that the amount of power supplied from the transmission (TX) resonator  324  of the stand  320  to the reception (RX) resonator  424  of the power unit  312  begins to decrease. Further, according to an embodiment of the disclosure,  FIG.  5 C  is a circuit diagram showing the current flow of within the display module  310  and the operating state of the light emitting unit  414 , after the display module  310  is moved farther away from the support surface of the stand  320  than in  FIG.  5 B  so that the amount of power supplied from the transmission (TX) resonator  324  of the stand  320  to the reception (RX) resonator  424  of the power unit  312  drops below a predetermined level (e.g., zero). Although  FIGS.  5 A to  5 C  illustrate that the stand  320  has a rectangular shape, this is only for convenience of illustration. 
     In order to help the reader&#39;s better understanding, in each of  FIGS.  5 A to  5 C , only a portion of the circuit in the display module  310  through which current flows is indicated by a bold black line, and a remaining portion in which no current flows is indicated in gray. Further, in each of  FIGS.  5 A to  5 C , the contrast of the light emitting unit  414  is shown differently depending on an amount of the current I LED1  flowing through the light emitting unit  414  for each circumstance (the more current flowing through the light emitting unit  414 , the darker bold arrow being displayed, while the less current flowing therethrough, the thinner gray arrow being displayed). 
     Specifically, referring then to  FIG.  5 A , when the display module  310  may be coupled to the support surface of the stand  320  and disposed in place, an induced current in the reception (RX) resonator  424  of the display module  310  due to resonance with the transmission (TX) resonator  324  of the stand  320  may flow through the rectifying section  422  to the power storage  314  and the screen display unit  316 . For example, the charging current I charging  from the rectifying section  422  of the power unit  312  may flow through the charging diode D charge1  and the resistor R limit1  of the power storage  314  to the capacitor C to charge the capacitor C. 
     In this regard,  FIG.  6    shows changes in voltage and current at each part of the display module  310  over time, in the case of  FIG.  5 A  where the display module  310  of  FIG.  4    is coupled to the support surface of the stand  320  and disposed in place.  FIG.  6 ( a )  shows that after the display module  310  is positioned in place on the support surface of the stand  320  at a timing point to, the capacitor voltage V c  gradually increases to approach the input voltage V input  from the power unit  312 , as the charging current I charging  from the rectifying section  422  of the power unit  312  flows through the charging diode D charge1  and the resistor R limit1  of the power storage  314  so as to charge the capacitor C. In this regard, the charging current I charging  flowing through the power storage  314  may be determined according to the following equation.  FIG.  6 ( b )  shows that the charging current I charging  decreases as V c  increases as in  FIG.  6 ( a ) . 
     
       
         
           
             
               I 
               charging 
             
             = 
             
               
                 
                   V 
                   input 
                 
                 - 
                 
                   V 
                   c 
                 
                 - 
                 
                   V 
                   F 
                 
               
               
                 R 
                 
                   limit 
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     According to an embodiment of the disclosure, a sum of the charging current I charging  flowing into the capacitor C through the charging diode D charge1  and the resistor R limit1  of the power storage  314  and the driving current I powering  flowing into the driver board  412  may be a constant value determined depending on a wireless transmission power transmitted/received between the transmission (TX) resonator  324  and the reception (RX) resonator  424 .  FIG.  6 ( c )  shows that the sum of the charging current I charging  and the driving current I powering  is controlled to a certain constant value below a rated current value I WPT_OCP  of the wireless power transmission. 
     In the meantime, due to the resistor R limit1  disposed to prevent possible damage to the circuit owing to inflow of rush current, a charging time of the capacitor C of the power storage  314  may lengthen. To deal with this problem of increased charging time in the driver board  412 , a driving current I powering  at initial charging stage may first be set to be a low value and then be gradually increased. For example, according to an embodiment of the disclosure, during the initial time of charging the capacitor C, the driver board  412  can control the luminance of the light emitting unit  414  (i.e., the current I LED1  for the light emitting unit  414 ) to gradually increase the driving current I powering  from the low value (refer to  FIG.  6 ( d ) ). According to an embodiment of the disclosure, since the driver board  412  can obtain a measured value of a voltage V c  across the capacitor C and a voltage drop VF across the charging diode D charge1  is of a fixed value, a value of the charging current I charging  can be obtained from the aforementioned equation. According to an embodiment of the disclosure, as the charging current I charging  is decreasing, the driver board  412  can make an appropriate control of the driving current I powering  so that the sum of the charging current I charging  and the driving current I powering  is to be a certain constant value. 
     Referring then to  FIG.  5 B , the display module  310  is just starting to deviate from the original position on the support surface of the stand  320  to be slightly separated from the support surface. Referring then to  FIG.  5 C , the display module  310  is being farther away from the support surface of the stand  320  than in  FIG.  5 B . In this context,  FIG.  7    shows changes in voltage and current at each part of the display module  310  and respective states of a switch SW over time during which the display module  310  gets detached from its original position on the support surface of the stand  320  and gradually moves away therefrom as shown in  FIGS.  5 B and  5 C . 
     As shown in  FIG.  5 B , since the capacitor C is already in a fully charged state, and the current supplied through the electromagnetic induction between the transmission (TX) resonator  324  of the stand  320  and the reception (RX) resonator  424  of the display module  310  passing through the rectifying section  422  flows only toward the screen display unit  316 . Here, as the display module  310  departs from the support surface of the stand  320  and thus the received voltage at the reception (TX) resonator  424  gradually decreases, the voltage V in  of the driving current I powering  flowing from the power unit  312  toward the screen display unit  316  may begin to gradually decrease. As described above, the screen display unit  316  can continuously measure the voltage V in  of the received driving current I powering . As the display module  310  begins to deviate from the support surface of the stand  320 , the voltage V in  of the driving current I powering  measured by the screen display unit  316  gradually gets lower. 
       FIG.  7 ( a )  shows a change in voltage V in  measured by the screen display unit  316  over time during which the display module  310  moves away from the support surface of the stand  320 . As illustrated in  FIG.  7 ( a ) , the display module  310  begins to depart from the support surface of the stand  320  at time t 1 , and then the voltage V in  may sharply decrease until it reaches time t 2 . According to an embodiment of the disclosure, the driver board  412  of the screen display unit  316  may compare the voltage V in  with a threshold value V th1 , and then identify that the voltage V in  falls below the threshold value V th1  at time t 2 . According to an embodiment of the disclosure, at this timing point t 2 , the driver board  412  may enter a power saving mode to reduce power consumed by the screen display unit  316 . According to an embodiment of the disclosure, when the driver board  412  enters the power saving mode, it can significantly reduce the luminance of the light emitting unit  414  to darken the screen. In  FIG.  5 B , the light emitting unit  414  is represented more dimly compared to that of  FIG.  5 A  to indicate that its luminance is significantly lowered. In  FIG.  7 ( c )  is illustrated that the current I LED1  for the light emitting unit  414  is greatly reduced from the timing point t 2 . Further,  FIG.  7 ( a )  shows that the rate of decrease of the voltage V in  is reduced compared to that before the timing point t 2 , at which the power saving mode is started so that the luminance of the light emitting unit  414  is lowered. 
     Referring again to  FIG.  7 ( a ) , it is shown that after the voltage V in  falls below the threshold value V th1  at a timing point t 2  as described above, the voltage V in  falls to a new threshold value V th2  which is lower than the threshold value V th1  at a timing point t 3 . As seen from  FIG.  5 C , this is because the display module  310  is further spaced apart from the support surface of the stand  320  and thus, the reception voltage of the reception (TX) resonator  424  got lower than that of  FIG.  5 B . According to an embodiment of the disclosure, the driver board  412  may compare the voltage V in  with the threshold value V th2 , and enter the ultra-power saving mode when the voltage V in  reaches the threshold value V th2  at a timing point t 3 . According to an embodiment of the disclosure, when entering the ultra-power saving mode, the driver board  412  may turn OFF each light emitting device of the light emitting unit  414  while maintaining a turned-on state of the screen display unit  316  itself. According to various embodiments of the disclosure, even if each light emitting device of the light emitting unit  414  is turned OFF in the ultra-power saving mode, since the turned-on state of the screen display unit  316  is maintained, the storage state of image information for the screen display can be maintained. Thus, when the power supply is resumed and exits from the power saving mode and/or the ultra-power saving mode, the screen display unit  316  can quickly restore the screen display with the maintained image information without re-booting or re-starting up. In  FIG.  5 C , it is illustrated that the light emitting unit  414  is represented more dimly than that of  FIG.  5 B  to indicate that each light emitting device thereof is turned OFF, and in  FIG.  7 ( c ) , it is illustrated that the current I LED1  for the light emitting unit  414  becomes almost zero from the timing point t 3 . Meanwhile, according to an embodiment of the disclosure, as shown in  FIG.  7 ( d ) , the switch SW may be controlled to be turned ON, from the time t 3  when the voltage V in  drops to the threshold value V th2  and the driver board  412  enters the ultra-power saving mode. When the switch SW is turned ON, a discharge current path of the power storage  314  may be activated, and the current charged in the capacitor C may be discharged to flow toward the driver board  412  of the screen display unit  316 . In this circumstance, as shown in  FIG.  7 ( a ) , the voltage V in  of the driving current I powering  for the driver board  412  may be temporarily increased again and then gradually lowered along with consumption of charging current of the capacitor C. In  FIG.  7 ( b ) , it is also shown that the charging voltage V c  of the capacitor C gradually decreases after the switch SW is turned ON at the timing point t 3 . 
     In the meantime, according to an embodiment of the disclosure, when the driver board  412  enters the ultra-power saving mode and turns OFF each light emitting device of the light emitting unit  414  as shown in  FIG.  5 C , the alarm unit  416  may be turned ON under the control of the driver board  412 . The alarm unit  416  may notify the user that the entirety of the display module  310  is not completely turned OFF, even though each light emitting device of the light emitting unit  414  is turned OFF. In  FIG.  5 C , the alarm unit  416  is illustrated as a separate lamp, but the present disclosure is not limited thereto. As described above, according to another embodiment of the disclosure, the alarm unit may include various audio/visual elements with one or more lamps or beepers. Alternatively, the alarm unit may be composed of some of the light emitting devices of the light emitting unit for the screen display (e.g., one or more light emitting diodes). 
     According to an embodiment of the disclosure, as described with reference to  FIGS.  5 A,  5 B,  5 C and  7   , the system may enter the power saving mode and/or the ultra-power saving mode in a stepwise manner, while the amount of power input is temporarily reduced or stopped as the display module is moved away from the support surface of the stand. According to another embodiment of the disclosure, when the amount of the input power is temporarily reduced or stopped as the display module is moved away from the support surface of the stand, the display module may immediately enter the ultra-power saving mode to extremely limit the power consumption. According to various embodiments of the disclosure, the display module can reduce its power consumption to consume minimal power only for maintaining its turned-on state (e.g., maintaining the storage state of image information for the screen display) through the power saving mode and/or the ultra-power saving mode, thereby enabling securing a longer standby time up until the power supplying from the stand is normally resumed again. 
       FIG.  8    is a diagram illustrating an example of use in which the display module  310  is pivoted and rearranged on the stand  320 , according to an embodiment of the disclosure. According to an embodiment of the disclosure, a display state of a display screen on the display module  310  may change in two stages, that is, a power saving mode and an ultra-power saving mode, until the display module  310  is rearranged on the stand  320  after deviating from its original position, as shown in  FIG.  5   . 
     As shown in  FIG.  8    at (a), the display module  310  is disposed in an original position on the stand  320  (e.g., a preferred placement position that can implement the maximum wireless power transmission) in landscape mode and displaying the screen. Specifically, although not shown herein, the power unit  312  of the display module  310  may be receiving a sufficient amount of power from the stand  320  in a wireless manner. Further, although not shown, the power supplied from the stand  320  may be stored in the power storage  314  of the display module  310 . 
     Then, in  FIG.  8    at (b), it is shown an initial moving situation at which the display module  310  starts to move away from its original position with respect to the stand  320 . As illustrated, it can be seen that the display module  310  enters the power saving mode, maintaining the display state of the screen, but the overall luminance of the screen gets lowered (or dimmed). 
     Now, as shown in  FIG.  8    at (c), the display module  310  moved further away from the stand  320  and the display module  310  has entered the ultra-power saving mode. As shown, the entire screen has been turned OFF. Even though the entire screen has been turned OFF, a lamp of the alarm unit  416  of the display module  310  is turned ON to indicate that the display module  310  is not completely turned OFF, but is in the ultra-power saving mode. 
     In  FIG.  8    at (d), it is illustrated that the display module  310  has been completely pivoted from the landscape mode to the portrait mode and rearranged in the proper position on the stand  320 . As illustrated, the screen display may exit from the power saving mode and/or the ultra-power saving mode to restore back the luminance state in its normal operation. According to various embodiments of the disclosure, during transitioning from  FIG.  8 ( c )  to  FIG.  8 ( d ) , the display module  310  may immediately restore the screen display illumination state without any restarting up process. Although not shown herein, the power unit  312  of the display module  310  at  FIG.  8 ( d )  may be receiving a sufficient amount of power from the stand  320  in a wireless manner again. Further, although not shown herein, the power storage  314  of the display module  310  may be charged again by the power supplied from the stand  320 . 
     Hereinafter, referring to  FIGS.  9 A,  9 B,  10 ,  11 A,  11 B, and  12   , description is made to the configuration and operation of a display system  900  (e.g., the display system  100  or  200  of  FIGS.  1  and  2   ) according to another embodiment of the disclosure. The display system  900  may include a stand  920  and a display module  910 . 
     First,  FIG.  9 A  is a side view schematically illustrating the stand  920  and the display module  910  coupled to the stand  920 , according to an embodiment of the disclosure, and then,  FIG.  9 B  is a graph conceptually illustrating a change in voltage in the display module  920  depending upon a distance from the stand  920  illustrated in  FIG.  9 A . 
     According to an embodiment of the disclosure, as shown in  FIG.  9 A , each of the support surfaces  922   a  and  922   b  on both sides of the stand  920  may be provided with a pair of transmitting electrodes  924   a  and  924   b  for transmitting power to the display module  910  in a wireless manner. Further, according to an embodiment of the disclosure, as shown in  FIG.  9 A , a pair of receiving electrodes  912  for receiving the power in contact with the transmitting electrodes  924   a  and  924   b  of the stand  920  may be provided on the back side of the display module  910 . According to an embodiment of the disclosure, the receiving electrodes  912  of the display module  910  may be respectively disposed to come into contact with the transmitting electrodes  924   a  on the support surface  922   a  to receive the power from the stand  920 . The receiving electrodes  912  of the display module  910  may be arranged to come into respectively contact with the transmitting electrodes  924   b  on the support surface  922   b  to receive the power from the stand  920 , as shown in  FIG.  9 A . In  FIG.  9 A , each of the transmitting electrodes  924   a  and  924   b  disposed on each of the support surfaces  922   a  and  922   b  is illustrated to protrude from the corresponding support surface, but the present disclosure is not limited thereto. Further, although the receiving electrodes  912  of the display module  910  is illustrated in a shape of protruding from the back side of the display module  910 , the present disclosure is not limited thereto. According to various embodiments of the disclosure, each of the transmitting electrodes provided in the stand and the receiving electrodes of the display module may have various shapes and arrangements enabling safe and efficient contacts and power transmissions. 
     As shown in  FIG.  9 A , in case where the display module  910  is configured to receive power from the stand  920  in a wireless manner through a physical contact between the electrodes of the stand  920  and the display module  910 , the reception voltage level of the display module  910  may abruptly drop to zero, as shown in  FIG.  9 B , at the moment when the receiving electrodes  912  of the display module  910  are separated or decoupled from the transmitting electrodes  924   a  and  924   b  of the stand  920 . This is because the power supply from the stand  920  to the display module  910  is cut off. 
       FIG.  10    is a diagram illustrating an exemplary circuit configuration of the display module  910  of  FIG.  9 A  according to an embodiment of the disclosure. As illustrated, the display module  910  may include receiving electrodes  912 , a power storage  914 , and a screen display unit  916 . 
     Referring to  FIG.  10   , the receiving electrodes  912  may receive power via the contact with the transmitting electrodes  924   a  or  924   b  of the stand  920  as described above with reference to  FIG.  9 A , for example. In the embodiment of the present disclosure where the display module  910  is configured to receive power through electrode contact, since a resonator circuit configuration for power transmission is not necessary, the display module  910  may be manufactured with a lower cost, compared to the display module  310  according to the embodiments described above with reference to  FIGS.  3  to  8   . 
     According to an embodiment of the disclosure, as shown in  FIG.  10   , the power storage  914  may be connected between the receiving electrodes  912  in parallel with the screen display unit  916 . According to an embodiment of the disclosure, the power storage  914  may include a power storage element, for example, a mass power storage device SC (e.g., super capacitor), a charging diode D charge2  delivering a charging current I super_cap  from one of the receiving electrodes  912  to the mass power storage device SC, and a resistor R limit2  connected between the mass power storage device SC and the charging diode D charge2 . According to an embodiment of the disclosure, in the display module  910  configured to receive power with the electrode contact, as described above with reference to  FIG.  9 B , the power supply to the receiving electrodes  912  is immediately interrupted at the moment when the electrode contact is released, and thus, the mass power storage device SC can be used to reserve enough charging power to wait until the power is properly resumed back again. 
     Since the mass power storage device SC may cause inrush current to flow into the circuit, the resistor R limit2  is disposed to prevent the circuit damage from the inrush current. According to an embodiment of the disclosure, as shown in  FIG.  10   , the power storage  914  may further include a sensing resistor Rsense for measuring the current I super_cap  flowing in the mass power storage device SC. According to an embodiment of the disclosure, as shown in  FIG.  10   , the power storage  914  may include a discharge diode D discharge  configured to be connected to a point between the mass power storage device SC and the resistor R limit2  and provide a discharge current path for the current discharged from the mass power storage device SC. The power storage  914  according to the embodiment of the disclosure may adopt a discharge diode D discharge  for the discharge current path, rather than a switch in the power storage  314  shown in  FIGS.  3  and  4    so that the display module  910  may be manufacture at a relatively lower unit cost. 
     According to an embodiment of the disclosure, as shown in  FIG.  10   , the screen display unit  916  may be connected to the receiving electrodes  912 . According to an embodiment of the disclosure, the screen display unit  916  may include a driver board  1002 , a light emitting unit  1004 , and an alarm unit  1006 . 
     According to an embodiment of the disclosure, the driver board  1002  may control the overall operation of the light emitting unit  1004  and the alarm unit  1006 . According to an embodiment of the disclosure, the driver board  1002  may receive the driving current I powering2  applied from the receiving electrodes  912  or discharged from the mass power storage device SC. The driver board  1002  may provide an operating current for the light emitting unit  1004  and the alarm unit  1006 . According to an embodiment of the disclosure, the driver board  1002  may store, for example, broadcasting or other various image information received or acquired from the outside in a wired or wireless manner, and based on the image information, control the light emission and luminance of each light emitting device of the light emitting unit  1004  (e.g., the operating current I LED2  for the light emitting unit  1004 ), for displaying visual information, video or images on a screen. According to an embodiment of the disclosure, the driver board  1002  may sense the current I super_cap  on the power storage  914 , and based on the sensed current I super_cap , control each light emitting device of the light emitting unit  1004  to operate in an ultra-power saving mode. 
     According to an embodiment of the disclosure, the light emitting unit  1004  may include a plurality of light emitting devices connected in series, for example, a plurality of light emitting diodes. Referring to  FIG.  10   , the light emitting unit  1004  is illustrated as having one row of light emitting diodes connected in series, but the present disclosure is not limited thereto. According to various embodiments of the disclosure, the light emitting unit  1004  may include an array or arrays of various numbers of light emitting devices connected in various ways. 
     As shown in  FIG.  10   , the alarm unit  1006  may include one lamp, but the present disclosure is not limited thereto. As described above with reference to  FIG.  5   , according to various embodiments of the disclosure, the alarm unit  1006  may include various elements or devices that provide a visual and/or audible alarm signal indicating that the light emitting unit  1004  is operating in the ultra-power saving mode. 
       FIGS.  11 A and  11 B  are diagrams respectively showing a current flow generated in the display module  910  and an operating status of the light emitting unit  1004 , depending upon a relative position between the display module  910  and the stand  920  of  FIG.  9   , according to an embodiment of the disclosure. More specifically,  FIG.  11 A  shows an initial current flow within the display module  910 , when the display module  910  is coupled and disposed on the support surface of the stand  920  so that a sufficient amount of power is supplied from the transmitting electrodes  924  of the stand  920  to the receiving electrodes  912 , according to an embodiment of the disclosure. Further, according to an embodiment of the disclosure,  FIG.  11 B  shows the current flow within the display module  910  when the display module  910  is separated from the support surface of the stand  920  so that the receiving electrodes  912  are not supplied with the power from the transmitting electrodes  924  of the stand  920 . As in the case of  FIG.  5   , in  FIG.  11   , the stand  920  is illustrated as having a rectangular shape, but this is only for convenience of illustration. As in the case of  FIG.  5   , it is noted in  FIG.  11    that only a portion of the display module  910  through which the current flows is indicated by a bold black line, while a remaining portion through which no current flows is indicated dimly in gray. Likewise, it is noted in each of  FIGS.  11 A and  11 B  that the contrast of the light emitting unit  1004  is represented differently depending on whether the current I LED2  flows in the light emitting unit  1004 . 
     Referring to  FIG.  11 A , the display module  910  may be coupled to the support surface of the stand  920  to be disposed in place. A current may flow to the power storage  914  and the screen display unit  916  of the display module  910  through the contact of the receiving electrodes  912  of the display module  910  with the transmitting electrodes  924  of the stand  920 . For example, the current I super_cap  from the receiving electrodes  912  may flow to the mass power storage device SC through the charging diode D charge2  and the resistor R limit2  of the power storage  914  and may charge the mass power storage device SC. Further, the driving current I powering2  from the receiving electrodes  912  may flow to the driver board  1002 . According to an embodiment of the disclosure, the driver board  1002  may receive the driving current I powering2  and supply the current I LED2  for the light emitting unit  1004 . 
     Then, referring to  FIG.  11 B , the receiving electrodes  912  of the display module  910  may be separated from the transmitting electrodes  924  on the support surface of the stand  920  so that no power is supplied from the stand  920 . In this context,  FIG.  12    shows changes in voltage and current at each part of the display module  910  when the power supply is cut off between the receiving electrodes  912  of the display module  910  and the transmitting electrodes  924  of the stand  920 . 
     According to an embodiment of the disclosure, when the power supply from the transmitting electrodes  924  of the stand  920  to the receiving electrodes  912  of the display  910  is interrupted, the current stored in the mass power storage device SC may start to flow toward the driver board  1002  through the discharge diode D discharge . In this connection,  FIGS.  12 A and  12 B  show that at a timing point t 4  when the receiving electrodes  912  are detached from the transmitting electrodes  924 , a discharge current starts to flow from the mass power storage device SC to get a voltage V super_cap  of the mass power storage device SC sharply decrease so that the current I super_cap  flowing through the mass power storage device SC becomes relatively large negative current (that is, the current flow direction over the mass power storage device SC being reversed). 
     According to an embodiment of the disclosure, the driver board  1002  may detect the current I super_cap  flowing over the mass power storage device SC as described above, and thus, the driver board  920  may recognize that the current I super_cap  has become a negative current (that is, the current direction over the mass power storage device SC being changed), when the display module  910  is positioned away from the stand  920  and the current stored in the mass power storage device SC is caused to flow toward the driver board  1002  through the discharge diode D discharge . According to an embodiment of the disclosure, when the driver board  1002  recognizes that the current I super_cap  has become a negative current, it enters the ultra-power saving mode and may turn OFF each light emitting device of the light emitting unit  1004  while keeping the turned-on state of the screen display unit  916 . In  FIG.  11 B , the light emitting unit  1004  is represented dimly, compared to that of  FIG.  11 A , to indicate that the light emitting unit  1004  is in a turned-off state. 
     According to various embodiments of the disclosure, even if the light emitting unit  1004  is turned OFF in the ultra-power saving mode, the screen display unit  916  is maintained to be turned on. Thus, the stored image information for the screen display can be maintained. Therefore, when exiting from the ultra-power saving mode, the screen display unit  916  will be able to quickly restore the screen display using the maintained image information without rebooting or restarting up. As shown in  FIG.  11 B , the driver board  1002  may turn ON the alarm unit  1006  when it enters the ultra-power saving mode to turn OFF the light emitting unit  1004 , thereby informing the user that not all the display module is turned OFF. 
     According to an embodiment of the disclosure, as shown in  FIGS.  10  and  11   , when the display module  910  is configured to receive power by an electrode contact, the power supply to the receiving electrodes  912  may be immediately disconnected as soon as the electrode contact is released as described above. Thus, when the power supply is disconnected, the display module  910  may directly enter the ultra-power saving mode to turn OFF the entire light emitting unit  1004 , instead of entering the power saving mode and the ultra-power saving mode in a stepwise manner, so as to secure a relatively long waiting time until the power supply to the display module  910  is properly resumed back again, but the present disclosure is not limited thereto. According to another embodiment of the disclosure, even in the case of a display module configured to receive electric power with the electrode contact, for example, if the capacity of the mass power storage device SC is very large, the display module may first operate to reduce the luminance of the light emitting devices of the light emitting unit, instead of turning OFF the light emitting devices of the light emitting unit after the power supply from the stand is stopped, similarly to the power saving mode discussed in reference to  FIG.  5 B . 
     According to another embodiment of the disclosure, even in the case of the display module configured to receive power with the electrode contact, the display module may operate to turn OFF only some of the light emitting devices of the light emitting unit, instead of turning OFF all the light emitting devices of the light emitting unit after the power supply from the stand to the display module is interrupted. 
     Meanwhile, as shown in  FIGS.  12 A and  12 B , at a timing point t 5 , a rate of decrease in the voltage V super_cap  in the mass power storage device SC is reduced and the current I super_cap  becomes relatively small negative current. This may result from the driver board  1002  entering the ultra-power saving mode at the timing point is and turning OFF the light emitting unit  1004  as described above. In this context,  FIG.  12 C  shows that the current I LED2  for the light emitting unit  1004  becomes almost zero from the timing point t 5 . 
       FIG.  13    is a diagram schematically illustrating a configuration of an exemplary display module  1310  in which a part of an internal circuit of the display module  910  shown in  FIG.  11 B  is modified. Similar to the display module  910  shown in  FIG.  11 B , the display module  1310  shown in  FIG.  13    may include receiving electrodes  1312 , a power storage  1314 , and a screen display unit  1316 . Similar to that shown in  FIG.  11 B , the display module  1310  shown in  FIG.  13    is in a state in which the power supply to the display module  1310  through the receiving electrodes  1312  is stopped. 
     Compared with the display module  910  of  FIG.  11 B , the display module  1310  of  FIG.  13    is different in structure in that it may be configured to utilize at least one or more light emitting devices  1306  of the light emitting unit  1304  as an alarm unit, instead of having a separate alarm unit (e.g., a separate lamp). According to an embodiment of the disclosure, when the power supply through the receiving electrodes  1312  is interrupted, the display module  1310  may enter a power saving mode or an ultra-power saving mode to turn OFF the light emitting unit  1304  via the driving board  1302 , while allowing the at least one or more of the light emitting devices partially constituting the light emitting unit  1304 , for example, the light emitting device  1306 , to maintain its turned ON state to operate as an alarm unit, as shown in  FIG.  13   . Although  FIG.  13    illustrates that one light emitting device  1306  operates as the alarm unit, which maintains its light emitting state even in either the power saving mode or the ultra-power saving mode, this is only for convenience of illustration and description and the present disclosure is not limited thereto. According to another embodiment of the disclosure, when the display module enters the power saving mode or the ultra-power saving mode, the display module  1310  may be configured so that a greater number of light emitting devices of the light emitting unit  1304  may operate as an alarm unit to maintain the light emitting state. According to an embodiment of the disclosure, the display module  1310  may indicate, similar to the alarm unit  1006  in the display module  910  described above, to the user that the display module  1310  is currently maintaining its turned-on state, through one or more light emitting devices keeping their light emitting state. 
     According to an embodiment of the disclosure, as shown in  FIG.  13   , when the display module  1310  enters the power saving or the ultra-power saving mode to turn OFF the light emitting devices of the light emitting unit  1304  while maintaining the light emitting state (i.e., turned-on state) of some of light emitting devices  1306  predetermined to operate as an alarm unit, it may operate to display predetermined information through some of the light emitting devices  1306  maintaining the light emitting state. According to an embodiment of the disclosure, for example, the display module  1310  may display, via the light emitting devices  1306  configured to maintain their light emitting state even in either the power saving or the ultra-power saving mode, information of the maximum remaining time duration for which the display module  1310  is capable of maintaining its turned-on state before resuming of the power supply from the outside, but the present disclosure is not limited thereto. 
     In this context,  FIG.  14    shows an example of using the display module  1310  in which the display module  1310  is pivoted from its original position and re-positioned on the stand  132 . Although not specifically illustrated, the stand  1320  may include transmitting electrodes capable of supplying power for the display module  1301  as shown in  FIG.  9 A . 
     As shown in (a) of  FIG.  14   , the display module  1310  is disposed on the stand  1320  in landscape mode to display a screen. Although not shown specifically, the display module  1310  may be receiving a sufficient amount of power from the stand  1320 . Further, although not shown, the power supplied from the stand  1320  may be stored in the power storage  1314  of the display module  1310 . 
     Then, as shown in (b) of  FIG.  14   , the display module  1310  starts to move away from its original position with respect to the stand  1320 . As illustrated above, when the display module  1310  is separated from the stand  1320 , it may immediately enter the ultra-power saving mode to turn OFF light emitting devices corresponding to most of the screen are turned OFF. However, as shown in (b) of  FIG.  14   , even though the display module  1310  enters the ultra-power saving mode to turn OFF those light emitting devices corresponding to most of the screen some of light emitting devices corresponding to a designated part of the screen (e.g., a lowermost right section of the screen, corresponding to those light emitting devices  1306  predetermined to operate as an alarm unit to maintain the light emitting state even in ultra-power saving mode) may maintain their light emitting state, as described above referring to  FIG.  13   . According to an embodiment of the disclosure, as shown in (b) of  FIG.  14   , the display module  1310  may control the light emitting devices  1306  on a part of the screen portion  1406  to operate as an alarm unit to provide predetermined display information informing of the ultra-power saving mode. According to an embodiment of the disclosure, as shown in (b) of  FIG.  14   , the display module  1310  may display, in the lowermost right section  1406  of the screen, the maximum remaining standby time duration or count (for example, a number 9 in (b) of  FIG.  14   ) during which the display module  1310  can maintain the turned-on state in the ultra-power saving mode without a resumption of power supply from the outside, but the present disclosure is not limited thereto. 
     Referring to (c) of  FIG.  14   , it is shown a situation in which the display module  1310  is pivotally rotated further away from the stand  1320  than that of  FIG.  14  ( b ) . In (c) of  FIG.  14   , the ultra-power saving mode is maintained and most of the light emitting devices on the screen are still turned OFF. In the lowermost right part  1406  of the screen, the updated maximum remaining standby time or count (e.g., the number 5 decreased than the number 9 in (b) of  FIG.  14   ) during which the display module  1310  can maintain the turned-on state without a resumption of the power supply from the outside. 
     Referring then to (d) of  FIG.  14   , it is shown a state in which the display module  1310  has been completely pivoted from a landscape mode to a portrait mode and then re-positioned in place on the stand  1320 . As shown in (d) of  FIG.  14   , the screen display is recovered from the ultra-power saving mode and restored to the original luminance state in the normal operation. Although not shown therein, the receiving electrodes  1312  of the display module  1310  may again receive electric power from the stand  1320  through the electrode contact. Further, although not shown herein, the power supplied from the stand  1320  may be stored again in the power storage  1314  of the display module  1310 . 
     The terms used in the present disclosure are only used to describe specific embodiments and are not intended to limit the present disclosure thereto. For example, an element expressed in a singular form should be understood as a concept including a plurality of elements, unless the context explicitly means only the singular. It should be understood that the term ‘and/or’ as used in this disclosure encompasses any and all possible combinations by one or more of the enumerated items. As used in the present disclosure, the terms such as ‘comprise’, ‘have’, ‘include’ and so on are only intended to designate that the features, components, parts, or combinations thereof described in the present disclosure exist, and the use of these terms is not intended to exclude the possibility of the presence or addition of one or more other features, components, parts, or combinations thereof. Expressions such as ‘first’, ‘second’, and so on used in the present disclosure may modify various components regardless of order and/or importance, and are only used to distinguish one component from other components and not used to limit the corresponding components. 
     The expression ‘configured to’ as used in this disclosure may be interchangeably used with, for example, ‘adapted to/for’, ‘having the ability to’, ‘designed to’, ‘modified to’, ‘made to’, ‘capable of’ or the like, according to the context. The term ‘configured to’ may not necessarily mean only ‘specially designed to’ in hardware. Instead, in some circumstances, the expression ‘a device configured to’ may mean that the device is ‘capable of’ with another device or parts. For example, ‘a device configured (or set) to perform the phrase A, B, and C’ may be a dedicated device for performing a corresponding operation or may mean a general-purpose device capable of performing various operations inclusive of the corresponding operation. 
     Although the foregoing description in the present disclosure has been made with respect to specific embodiments, it is to be understood that the present disclosure is not limited to the specific embodiments and encompasses all of the various modifications, equivalents, and/or substitutions of various embodiments.