A data driving circuit for displaying an image with a desired brightness comprises: a current digital-analog converter for generating a gradation current corresponding to external data, and for receiving a first current corresponding to the gradation current from a pixel via a data line; a current control unit for receiving a pixel current from the pixel via the data line, and for selectively increasing and decreasing a level of the first current in accordance with the received pixel current; and a selection unit for selectively connecting the data line to either the current digital-analog converter or the current control unit. An organic light emitting diode and a method of driving same are similarly configured. With these configurations, an image is displayed with desired brightness.