1. Field
An aspect of embodiments of the present invention relates to a DC-DC converter and an organic light emitting display using the same.
2. Description of the Related Art
Recently, various types of flat panel display devices have been developed that have reduced the weight and volume compared to cathode ray tube display devices. The flat panel display devices include a liquid crystal display, a field emission display, a plasma display panel, an organic light emitting display, and the like. Among these flat panel display devices, the organic light emitting display device displays images using organic light emitting diodes (OLEDs).
An organic light emitting diode includes an anode electrode, a cathode electrode and a light emitting layer positioned between the anode and cathode electrodes. When current flows in the direction from the anode electrode to the cathode electrode, the OLED emits light, so that a color can be expressed.
By employing organic light emitting diodes that are self-luminescent elements, the organic light emitting display device has several beneficial characteristics, including excellent color reproduction, thin thickness, and the like. Accordingly, the application fields for such devices have been widely extended to markets of mobile phones, PDAs, MP3 players and the like.
FIG. 1 is a graph showing changes in saturation point based on changes in the amount of current in an organic light emitting diode. The horizontal axis of the graph denotes the voltage of a ground power source, and the vertical axis of the graph denotes the amount of current that flows in the direction from an anode electrode to a cathode electrode of the organic light emitting diode.
Referring to FIG. 1, when saturation current is 150 mA, the voltage of the cathode electrode at a point where the OLED reaches a saturation point is 0 to −1 V. When the saturation current is 200 mA, the voltage of the cathode electrode at the point where the OLED reaches the saturation point is −1 to −2 V. When the saturation current is 250 mA, the voltage of the cathode electrode at the point where the OLED reaches the saturation point is below −2 V.
That is, the voltage of the cathode electrode is varied depending on the amount of saturation current. However, in an organic light emitting display, the voltage of the cathode electrode is generally fixed to a voltage corresponding to when the saturation current is greatest. That is, although it is less likely that images displayed in the organic light emitting display are all represented with the maximum gray level, the voltage of the cathode electrode is fixed to the voltage corresponding to when the saturation current is greatest. Therefore, waste of driving voltage, i.e., power consumption, is increased.
If the driving voltage is rapidly changed, noise is generated based on the change in driving voltage.