An organic light emitting display is provided. The organic light emitting display includes a display unit coupled to scan lines and data lines and including pixels configured to receive first and second power sources, and a DC-DC converter for generating the first and second power sources. The DC-DC converter includes first and second power source generating units for generating the first and second power sources from an input power source and for outputting the first and second power sources to first and second output ends, a controller for controlling driving of the first and second power source generating units, and first and second short sensing units for outputting first and second short sensing signals to the controller when voltages of the first and/or second output ends are greater than or equal to corresponding first and second reference voltages.