The present invention is related to a device (1) for the detection of direct and/or alternating current to be used in the realisation of highly sensitive amperometric measuring instruments or for the detection of differential faults along with automatic switches. The inventive device comprises a magnetic core (5) disposed in such a manner to surround at least one current-carrying conductor (6). A winding (10) surrounds the magnetic core (5) and is electrically connected to an electrical resistance (60). A voltage source (40) generates a drive voltage (Vexcit) which permits the circulation of a pick-up current (Iexcit) in the said winding (10) and in the said core (5). Amplification means (20) are used to detect the voltage (Vsense) at the terminals of the resistance (60) in order to generate a first signal (Vampl) which is representative of the above defined current (lexcit). The inventive device (1) also comprises a feedback adjustment circuit block (70) which acquires the first input signal (Vampl) in order to generate a second signal which inverts the said drive voltage (Vexcit) when the pick-up current (Iexcit) reaches preset values.