Disclosed herein is a device comprising a protection circuit configured to protect against a polarity reversal of the input DC power supply voltage, the protection circuit comprising an N-channel main transistor having a source coupled to an input terminal and having a drain coupled to an output terminal, a command circuit configured to render the main transistor blocked in the event of a polarity reversal and conducting otherwise, and a control circuit configured to dynamically adjust the bias of substrate regions of respective components connected to the main transistor by connecting the substrate regions either to the source or to the drain of the main transistor according to the value of the voltages present at the source and the drain of the main transistor and the type of conductivity of the substrate regions.