Hall current sensors come in two types: open-loop and closed-loop.

1Open-loop Hall current sensorAlso known as direct discharge Hall current sensor, its working principle is shown in the following figure:

When the primary current IP flows through a long wire, a magnetic field is generated in the annular magnetic core, and the magnitude of this magnetic field is proportional to the current flowing through the wire. The generated magnetic field is concentrated in the magnetic ring, measured and amplified by Hall elements in the air gap of the magnetic ring, and its output voltage VS reflects the primary current IP proportionally.

Due to the proportional relationship between the magnetic induction intensity in the annular magnetic core and the primary current, as long as the primary current is large enough, the annular magnetic core will inevitably saturate.

2闭环式霍尔电流传感器Also known as zero flux transformer or magnetic balance current sensor, its working principle is shown in the following figure:

The magnetic field generated by the primary current Ip in the magnetic core is compensated by the magnetic field generated by the secondary compensation coil current, so that the Hall device is in the working state of detecting zero magnetic flux. The compensation current Is proportionally reflects the primary current Ip. The specific working process is as follows: when a current passes through the main circuit, the magnetic field generated on the wire is concentrated by the magnetic core and induced to the Hall device. The generated signal output is used to drive the power transistor and make it conductive, thereby obtaining a compensation current Is. This current then generates a magnetic field through a multi turn winding, which is exactly opposite to the magnetic field generated by the measured current, thus compensating for the original magnetic field and gradually reducing the output of the Hall device. When the magnetic field generated by multiplying Ip with the number of turns is equal, Is no longer increases. At this point, the Hall device acts as an indicator of zero magnetic flux, and Ip can be tested using Is. When Ip changes, the balance is disrupted, and the Hall device outputs a signal, repeating the above process to reach balance again. Any change in the measured current will disrupt this balance. Once the magnetic field loses balance, the Hall device will output a signal. After power amplification, a corresponding current immediately flows through the secondary winding to compensate for the unbalanced magnetic field. The time required from magnetic field imbalance to re equilibrium is theoretically less than 1 μ s, which is a dynamic equilibrium process.

Therefore, from a macro perspective, the number of ampere turns of the secondary compensation current is always equal to the number of ampere turns of the primary measured current at any time.

When the closed-loop Hall current sensor is working normally, the magnetic flux of its primary winding and secondary winding cancel each other out, achieving magnetic balance, and the actual magnetic flux in the magnetic core is zero. However, this is only an ideal situation. In actual sensors, the output current capability of the secondary winding composed of electronic circuits is always limited. When there is an overload, if the secondary output is limited, the actual output current will be smaller than the theoretical current, and the magnetic balance will be broken. As long as the primary current continues to increase, the iron core will saturate.

Regardless of the type of Hall current sensor, magnetic saturation of the magnetic core may result in residual magnetism, and the output of the Hall sensor is related to the magnetic flux of the magnetic core. Therefore, even in the absence of input, a Hall current sensor with magnetic saturation will still output a certain DC signal.