Electric current sensor with wide passband

Electric current sensor for measuring a current flowing through a primary conductor, this sensor comprising:

• a magnetic circuit arranged to be coupled with said primary conductor,
• a secondary winding electromagnetically coupled with this magnetic circuit, each extremity of said secondary winding comprising a terminal, a damping resistance of said secondary winding, having a determined value and being connected between said terminals,
• a magnetic field detector arranged within an air gap of said magnetic circuit,
• a current supply device, controlled by the magnetic field detector and connected to a first terminal of said secondary winding so as to feed to the secondary winding a compensating current seeking to eliminate the magnetic field created in the air gap by the current flowing in the primary conductor, and
• a measuring resistor connected in series with the secondary winding, between the second terminal of said secondary winding and the ground, where the voltage drop across this resistors forms the measuring signal of the sensor,
• wherein the sensor further comprises:
• an auxiliary resistor which has the same value of resistance as the ohmic damping resistance of the secondary winding, having one extremity connected to said second terminal and another extremity connected to a differential amplifier
• said differential amplifier block arranged so as to measure the voltage appearing at the terminals of the secondary winding and to apply to said other extremity of said auxiliary resistor a voltage of the same size but opposite in direction to that appearing at the terminals of the secondary winding.