A Magnetic-Ring-Free TMR Current Sensor Eliminating Geomagnetic Influence for Noncontact Current Detection

In compact power electronic devices, magnetic-ring-free current sensors are increasingly preferred due to their compact size and lightweight nature. However, in high-precision small current measurements, the geomagnetic field can introduce substantial errors. To address this issue, a sensor chip using a bridge structure composed of four highly sensitive tunnel magnetoresistance (TMR) elements was employed, and a novel magnetic-ring-free current sensor was designed that eliminates geomagnetic field interference, thereby achieving precise small current measurements. This sensor operates in a zero-magnetic-flux state for the geomagnetic field, where the geomagnetic signal is fed back through a feedback coil, effectively canceling the geomagnetic field with the magnetic field generated in the feedback coil. This design enables the current sensor to achieve high-precision measurements. The experimental results showed that the current sensor achieved a sensitivity of 3.808 V/A and a measurement accuracy of ±1.854% within a sensing range of ±1.8 A. These findings offer a novel design strategy for future current sensors.