Abstract:
A DC-DC converter is provided including a switch unit, a coil, and a controller. The switch unit is coupled to an input power supply and is configured to transmit or not to transmit input power from the input power supply in accordance with a switching signal. The coil has a first terminal for receiving current output from the switch unit and a second terminal. The controller is coupled to the coil and is configured to operate or not to operate in accordance with an enable signal. The controller is configured to change a flow of current through the coil such that the second terminal of the coil is at a higher voltage than the first terminal of the coil.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0018314, filed on Feb. 28, 2008, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a direct current to direct current (DC-DC) converter and an organic light emitting display using the same, and more particularly to a DC-DC converter with decreased power consumption and an organic light emitting display using the same. 
         [0004]    2. Description of Related Art 
         [0005]    Recently, various flat panel displays have been developed with reduced weight and volume. The flat panel displays include a liquid crystal display, a field emission display, a plasma display panel, an organic light emitting display, and the like. 
         [0006]    Among others, the organic light emitting display displays an image using organic light emitting diodes (OLEDs) for generating light as a result of the recombination of electrons and holes. 
         [0007]    The OLED includes an anode electrode, a cathode electrode, and a light emitting layer positioned therebetween. If current flows in a direction from the anode electrode to the cathode electrode, the OLED emits light to represent colors. 
         [0008]    The organic light emitting display has various advantages such as an excellent color representation and a thin thickness so that it is widely used in a variety of applications, e.g., a PDA, an MP3, a monitor, and a TV, in addition to a cellular phone. 
         [0009]    When the organic light emitting display is used in a mobile device such as a cellular phone, a PDA, or an MP3 player, the organic light emitting display may be supplied power through a battery. However, if an amount of current consumed in the organic light emitting display is large, the mobile device cannot be used for a long time and the battery should be frequently exchanged. Therefore, it is desirable to reduce current consumption in the organic light emitting display. 
       SUMMARY OF THE INVENTION 
       [0010]    A DC-DC converter and an organic light emitting display using the same are provided with reducing leakage currents and therefore decreased power consumption. 
         [0011]    In an exemplary embodiment of the present invention, a DC-DC converter is provided including a switch unit, a coil, and a controller. The switch unit is coupled to an input power supply and is configured to transmit or not to transmit input power from the input power supply in accordance with a switching signal. The coil has a first terminal for receiving current output from the switch unit and a second terminal. The controller is coupled to the coil and is configured to operate or not to operate in accordance with an enable signal. The controller is configured to change a flow of current through the coil such that the second terminal of the coil is at a higher voltage than the first terminal of the coil. 
         [0012]    In one exemplary embodiment, the switching signal and the enable signal are synchronized with each other. 
         [0013]    In one exemplary embodiment, the switch unit switches the input power in accordance with the switching signal. 
         [0014]    In one exemplary embodiment, the switch unit includes a first input terminal coupled to the input power supply and a second input terminal for receiving the switching signal; a first switch having a first electrode coupled to the first input terminal, a second electrode coupled to a ground, and a gate coupled to the second input terminal; and a second switch having a first electrode coupled to the first input terminal, a second electrode coupled to an output terminal, and a gate coupled to the first input terminal through a resistor. 
         [0015]    In one exemplary embodiment, the input power supply comprises a battery. 
         [0016]    In an exemplary embodiment of the present invention, an organic light emitting display is providing including a display unit for displaying an image corresponding to a data signal and a scan signal; a data driver for providing the data signal to the display unit; a scan driver for providing the scan signal to the display unit; and a DC-DC converter for transferring driving power to the data driver and to the scan driver. The DC-DC converter includes a switch unit coupled to an input power supply and configured to transmit or not to transmit input power from the input power supply in accordance with a switching signal; a coil having a first terminal for receiving current output from the switch unit and a second terminal; and a controller coupled to the coil and configured to operate or not to operate in accordance with an enable signal, the controller configured to change a flow of current through the coil such that the second terminal of the coil is at a higher voltage than the first terminal of the coil. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The accompanying drawings, together with the specification illustrate exemplary embodiments of the present invention and serve to explain the principles of the present invention: 
           [0018]      FIG. 1  is a block diagram of an organic light emitting display according to an exemplary embodiment of the present invention; 
           [0019]      FIG. 2  is a circuit diagram showing a first exemplary embodiment of the DC-DC converter of  FIG. 1 ; 
           [0020]      FIG. 3  is a circuit/block diagram showing a second exemplary embodiment of the DC-DC converter of  FIG. 1 ; and 
           [0021]      FIG. 4  is a circuit diagram showing the switch unit of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereinafter, certain exemplary embodiments according to the present invention will be described with reference to the accompany drawings. Herein, when a first element is described as being coupled to a second element, the first element may be directly coupled to the second element or indirectly coupled to the second element via a third element. Further, some of the elements that are not essential to the complete understanding of the invention are omitted for clarity. Also, like reference numerals may refer to like elements throughout. 
         [0023]    Hereinafter, exemplary embodiments according to the present invention will be described with reference to the accompanying drawings. 
         [0024]      FIG. 1  is a block diagram of an organic light emitting display according to an exemplary embodiment of the present invention. The organic light emitting display according to an exemplary embodiment of the present invention includes a display unit  100 , a data driver  110 , a scan driver  120 , a DC-DC converter  130 , and a battery  140 . 
         [0025]    The display unit  100  includes a plurality of pixels  101 , wherein each pixel  101  includes an OLED for emitting light corresponding to a flow of current. The display unit  100  is arranged with a plurality of scan lines S 1 , S 2 , . . . , Sn- 1 , and Sn extending in a row direction for transferring scan signals, and a plurality of data lines D 1 , D 2 , . . . , Dm- 1 , and Dm extending in a column direction for transferring data signals. Also, the display unit  100  receives first power ELVDD and second power ELVSS. 
         [0026]    The data driver  110  receives RGB video data having red, blue, and green components to generate data signals. Further, the data driver  110  applies the generated data signals to the display unit  100  via the coupled data lines D 1 , D 2 , . . . , Dm- 1 , and Dm. 
         [0027]    The scan driver  120  transfers the scan signals to a specific row of the display unit  100 . The scan driver  120  applies the generated scan signals to the display unit  100  via the coupled scan lines S 1 , S 2 , . . . , Sn- 1 , and Sn. The pixel  101  receives the scan signals output from the scan driver  120  and the data signals output from the data driver  110 , and a driving current is generated in the pixel  101  for the OLED. 
         [0028]    The DC-DC converter  130  transfers the first power ELVDD and the second power ELVSS to the display unit  100 , and transfers driving voltage VDD to the data driver  110  and the scan driver  120 . The DC-DC converter  130  boosts and/or inverts voltage Vbat input from the battery  140  to generate the first power ELVDD and the second power ELVSS. 
         [0029]    The battery  140  supplies current having a voltage (e.g., a predetermined voltage) to the DC-DC converter  130  for a time period (e.g., a predetermined time period) to enable the organic light emitting display to be used without being coupled to a separate external power source. 
         [0030]      FIG. 2  is a circuit diagram showing a first exemplary embodiment of the DC-DC converter of  FIG. 1 . The DC-DC converter  130  includes an input terminal  210 , an output terminal  230 , and a controller  220  coupled therebetween. 
         [0031]    The input terminal  210  is coupled to battery  140  to receive input power from the battery  140 . The controller  220  includes a coil L 1  and generates electromotive force from the coil L 1  by switching power transferred from the input terminal  210 . The operation or non-operation of the controller  220  is controlled by an enable signal EN. The output terminal  230  receives current generated from the coil L 1  and outputs the current. 
         [0032]    If the operation of the controller  220  is stopped using the enable signal EN in order to stop the operation of the DC-DC converter  130 , the operation to block or to pass the current flowing through the coil L 1  is stopped. Because the current output from the battery  140  is direct current, the coil L 1  functions as a wire. Therefore, the current from the battery  140  passes through the coil L 1  to be output to the output terminal  230 . 
         [0033]    If the current is output through the output terminal  230 , the current is transferred to the data driver  110  and/or the scan driver  120  and the transferred current flows through the data driver  110  and/or the scan driver  120 . 
         [0034]    Therefore, the current stored in the battery  140  is continuously consumed. Thus, the current charged in the battery  140  is consumed even when the organic light emitting display is not used so that use time of the organic light emitting display is shortened. 
         [0035]      FIG. 3  is a circuitblock diagram showing a second exemplary embodiment of the DC-DC converter of  FIG. 1 . The DC-DC converter  130  includes an input terminal  310 , a controller  330 , an output terminal  340 , and a switch unit  320 . 
         [0036]    The input terminal  310  is coupled to battery  140  to receive input power from the battery  140 . The controller  330  includes a coil L 2  and generates electromotive force from the coil L 2  by switching power transferred from the input terminal  310 . The operation or non-operation of controller  330  is controlled through an enable signal EN. The output terminal  340  receives current generated from the coil L 2  and outputs the current. 
         [0037]    The switch unit  320  is coupled between the input terminal  310  and the controller  330  of the DC-DC converter  130 . In other words, the current output from the battery  140  is blocked from passing through the switch unit  320  or is allowed to pass through the switch unit  320 . If the current output from the battery  140  is allowed to pass through the switch unit  320 , the current is provided to the coil L 2  of the DC-DC converter  130 . Switch unit  320  receives a switching signal synchronized with the enable signal EN to perform a switching operation. Therefore, if the controller  330  operates by the enable signal EN, the switch unit  320  is turned on by the switching signal to transfer power from the battery  140  to the coil L 2 . If the operation of the controller  330  is stopped by the enable signal EN, the switch unit is turned off by the switching signal to block power output from the battery  140 , thereby preventing the power output from the battery  140  from being transferred to the coil L 2 . Therefore, when the operation of the controller  330  stops, the current generated from the battery  140  can be prevented from flowing through the coil L 2  so that power consumption in the organic light emitting display is reduced. 
         [0038]      FIG. 4  is a circuit diagram showing the switch unit of  FIG. 3 . The switch unit  320  includes a first switch Q 1  and a second switch Q 2 . 
         [0039]    A drain of the first switch Q 1  is coupled to a first node N 1 , a source of the first switch Q 1  is coupled to a ground voltage, and a gate of the first switch Q 1  is coupled to a switching signal such that the first switch Q 1  performs a switching operation by the switching signal. The first switch Q 1  is implemented as an NMOS transistor. 
         [0040]    If the switching signal is input in a high state, the first switch Q 1  is turned on. Accordingly, the first node N 1  is coupled to the ground voltage so that voltage of the first node N 1  becomes the ground voltage. Because the enable signal EN is synchronized with the switching signal, the enable signal EN becomes a high state and the controller  330  therefore operates. If the switching signal is input in a low state, the first switch Q 1  is turned off so that the first node N 1  becomes the voltage Vbat of the battery  140 . Because the enable signal EN is synchronized with the switching signal, the enable signal EN becomes a low state and the operation of the controller  330  therefore stops. 
         [0041]    A source of the second switch Q 2  is coupled to the battery  140  to receive voltage Vbat from the battery  140 , a drain of the second switch Q 2  is coupled to an output terminal Vout, and a gate of the second switch Q 2  is coupled to the first node N 1 . The second switch Q 2  is implemented as a PMOS transistor. 
         [0042]    If the voltage of the first node N 1  becomes the ground voltage by the first switch Q 1 , the second switch Q 2  is turned on. If the voltage of the first node N 1  becomes the voltage Vbat of the battery, the second switch Q 2  is turned off. In other words, the second switch Q 2  is turned on if the switching signal is in a high state, and the second switch Q 2  is turned off if the switching signal is in a low state. 
         [0043]    If the second switch Q 2  is turned on, power is transferred from the battery  140  to the output terminal Vout. If the second switch Q 2  is turned off, power from the battery  140  is blocked from being provided to the output terminal Vout. 
         [0044]    Therefore, when the controller  330  operates, the switch unit  320  transfers power from the battery  140  to the coil L 2 . When the controller  330  does not operate, the switch unit  320  prevents power from the battery  140  from being transferred to the coil L 2 . Therefore, power consumption is reduced by reducing a leakage current (i.e., current consumption). 
         [0045]    While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.