Difference between Open-Loop Electrical Current Sensor and Closed-Loop Electrical Current Sensor

In traditional closed-loop current sensing technology, its high precision has been widely used in industrial and automotive industries. By applying proprietary packaging technology and advanced integrated algorithms in a complex and fully integrated current sensor, manufacturers have developed a brand new magnetic electrical current sensor that achieves near-closed-loop accuracy with an open-loop sensor architecture.

Open-loop Hall Effect Current Sensor

Generally, an open-loop Hall effect current sensor uses a magnetic sensor to generate a voltage proportional to the current being sensed, which is then amplified into an analog signal output proportional to the current in the conductor. Structurally speaking, the conductor passes through the center of a ferromagnetic material to concentrate the magnetic field, while the magnetic sensor is placed in the gap of the ferromagnetic material. In an open-loop architecture, Hall effect current sensors may produce errors due to any nonlinearity and sensitivity drift with temperature.

Closed-loop Hall Effect Current Sensor

A closed-loop Hall effect current sensor uses a coil actively driven by the current sensor to generate a magnetic field opposite to the current in the conductor. This way, the Hall sensor always operates at a zero magnetic field operating point. The output signal is generated by a resistor whose voltage is proportional to the current in the coil, which is also proportional to the current in the magnetic core coil, but lacks translation details.

Open-loop vs. Closed-loop Hall Effect Current Sensor

Closed-loop current sensor requires not only a ferromagnetic core, but also a coil and extra high-power amplifier to drive the coil. Although closed-loop current sensing is more complex than open-loop architecture, it eliminates sensitivity errors related to Hall effect sensors since the system operates only at a zero magnetic field operating point. If designed properly, both closed-loop and open-loop Hall effect current sensors usually have similar zero amp output voltage performance, so their zero amp detection accuracy is very similar. Compared to the open-loop solution, the closed-loop sensor is larger in size and requires more PCB space. Since the closed-loop sensor requires a certain amount of current to drive the compensation coil, it has higher power consumption. In addition, the closed-loop sensor requires additional coils and driving circuits and is more expensive than the open-loop sensor.

The choice between open-loop and closed-loop Hall effect current sensors depends on accuracy and response time. If high accuracy is required, a closed-loop current sensor is usually chosen since it can eliminate the system sensitivity nonlinearity error mentioned above. In some applications, fast response is required to protect semiconductor devices and better control the current in the application. If there is enough accuracy and response time, an open-loop sensor is also an ideal choice due to its inherent advantages in size, power consumption, and other aspects. Advanced manufacturers have developed this brand new open-loop solution, which is smaller in size, high-precision, and fast-response, and more economical than the closed-loop solution.