A device for connection between supply buses in mixed power integrated circuits includes a diode in series with a transistor with an active p-ring in a semiconductor substrate. The active p-ring surrounds the source and drain of the transistor with a conductive region having the same conductivity type as the semiconductor substrate. A control circuit coupled to the p-ring applies a bias voltage in response to an ESD event affecting the first and second conductors. The bias voltage tends to inject carriers into the semiconductor substrate which enables discharge of the short voltage pulse via a parasitic SCR in the substrate from the anode of the diode to the source of the transistor.