Patent ID: 8698485
Filing Date: 2014-04-15
Classification: G01R

Abstract:
1. 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.