Current sensor operating in accordance with the principle of compensation

A current sensor, comprising:

• a primary coil, through which current to be measured flows, creating a first magnetic field;
• a secondary coil, through which a compensation current flows, generating a magnetic field compensating the first magnetic field of the primary coil;
• a gapped magnetic core, magnetically coupled to the two primary and secondary coils and concentrating the resulting magnetic field in its air gap;
• a terminating resistor connected in series with the secondary coil;
• sensor means located in the air gap and exposed to the resulting magnetic field of the primary and secondary coils;
• and
• a booster circuit connected downstream of the sensor means and feeds the compensation current to the secondary coil via the terminating resistor,
• wherein the booster circuit includes a switched mode amplifier with a pulse width and density modulator that generates a pulse width and density modulated voltage signal which drives the compensation current through the secondary coil winding, and wherein the switching frequency of the modulator is a function of the compensation current such that the switching frequency is high at small currents and low at high currents.