A display device, comprising: a display panel including pixels at crossing regions of data lines and scan lines; one or more source drive integrated circuits ICs to supply data voltages to the data lines; a scan driving circuit to supply scan signals to the scan lines; and driving voltage supply lines DVL1, DVL2 crossing test voltage lines TL connected to the output terminal of the source drive integrated circuits, wherein each source drive integrated circuit comprises: a source driving circuit to generate data voltages according to a source timing control signal and digital video data; plural output buffers to which first and second power voltages are supplied to output the data voltages from the source driving circuit to output terminals connected to the data lines; first voltage protection circuits to which first and second power voltages are supplied, connected between the plural output buffers and the output terminals, at least one further output buffer connected to the output terminal in contact with one of the test voltage lines TL and a second voltage protection circuit to which at least one of the voltages delivered by the driving voltage supply lines DVL1, DVL2 is supplied, connected between the at least one further output buffer and the output terminal; wherein the voltages DVL1, DVL2 delivered by the driving voltage supply lines are different to the first and second power voltages; and the at least one voltage supplied to the second voltage protection circuit is applied to the anode of a diode if the cathode of the diode is connected to the test line or to the cathode of the diode if the anode is connected to the test line. a display panel including pixels at crossing regions of data lines and scan lines; one or more source drive integrated circuits ICs to supply data voltages to the data lines; a scan driving circuit to supply scan signals to the scan lines; and driving voltage supply lines DVL1, DVL2 crossing test voltage lines TL connected to the output terminal of the source drive integrated circuits, wherein each source drive integrated circuit comprises: a source driving circuit to generate data voltages according to a source timing control signal and digital video data; plural output buffers to which first and second power voltages are supplied to output the data voltages from the source driving circuit to output terminals connected to the data lines; first voltage protection circuits to which first and second power voltages are supplied, connected between the plural output buffers and the output terminals, at least one further output buffer connected to the output terminal in contact with one of the test voltage lines TL and a second voltage protection circuit to which at least one of the voltages delivered by the driving voltage supply lines DVL1, DVL2 is supplied, connected between the at least one further output buffer and the output terminal; wherein the voltages DVL1, DVL2 delivered by the driving voltage supply lines are different to the first and second power voltages; and the at least one voltage supplied to the second voltage protection circuit is applied to the anode of a diode if the cathode of the diode is connected to the test line or to the cathode of the diode if the anode is connected to the test line. a source driving circuit to generate data voltages according to a source timing control signal and digital video data; plural output buffers to which first and second power voltages are supplied to output the data voltages from the source driving circuit to output terminals connected to the data lines; first voltage protection circuits to which first and second power voltages are supplied, connected between the plural output buffers and the output terminals, at least one further output buffer connected to the output terminal in contact with one of the test voltage lines TL and a second voltage protection circuit to which at least one of the voltages delivered by the driving voltage supply lines DVL1, DVL2 is supplied, connected between the at least one further output buffer and the output terminal; wherein the voltages DVL1, DVL2 delivered by the driving voltage supply lines are different to the first and second power voltages; and the at least one voltage supplied to the second voltage protection circuit is applied to the anode of a diode if the cathode of the diode is connected to the test line or to the cathode of the diode if the anode is connected to the test line.