With the rapid development of industries such as electric vehicles and energy storage, the demand for current detection is also increasing. However, for these scenarios, sensors such as Hall effect sensors, shunt resistors, current transformers (CTs), and Rogowski coils are more commonly used to accomplish the task.

In certain applications that require extreme precision in current measurement, or when the power supply system is in a high-interference magnetic field environment, the high accuracy and interference resistance of fluxgate sensors may make them a valuable choice. Moreover, with the popularization of open-loop fluxgate sensors and the subsequent cost reduction, they are expected to secure a place in power supply design.

Expensive Fluxgate Sensors

In today's electrical equipment, current sensors are very important. These sensors can sense the information of the current being measured and transform this information into an electrical signal or other forms of information output that meet certain standard requirements according to a certain rule. Current sensors have developed into various types, including Hall sensors, shunt resistors, current transformers, and fluxgate sensors, based on different application scenarios and technical requirements.

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Generally speaking, in power supply design, Hall effect sensors are more commonly used as current sensors due to their simplicity, cost-effectiveness, and adaptability. Hall sensors can directly measure the magnetic field caused by the current without complex signal processing, while providing good isolation and safety performance. In addition, the response speed of Hall sensors is fast, making them suitable for current monitoring in high-frequency switching power supplies.

Fluxgate sensors may be used in some current measurement applications that require extreme precision and sensitivity, such as in high-end power management systems that require high-precision current detection. However, they are rarely used in power supply design due to their high cost.

For example, according to some recent public data in the market, the price of an AC/DC zero-flux fluxgate current transformer is about 680 RMB, while the price of a closed-loop fluxgate current transformer is about 75 RMB. The price of a regular Hall sensor ranges from a few cents to several hundred RMB, which means that even a low-end fluxgate sensor may cost many times more than a Hall sensor.

The high cost is partly due to the core component of the fluxgate sensor being a high permeability magnetic core, usually made from special magnetic materials such as giant magnetostrictive alloys (such as Metglas, Permalloy, etc.). These materials have high magnetic permeability and low coercivity, but they are also relatively expensive.

At the same time, fluxgate sensors require precise magnetic circuit design and signal processing circuits, especially closed-loop fluxgate sensors, which include a feedback control loop to keep the magnetic core in an unsaturated state. Closed-loop systems require additional hardware and complex signal processing algorithms, increasing the complexity and cost of design and manufacturing.

Of course, if an open-loop fluxgate sensor design is used, since there is no closed-loop control system, they directly detect the changes in the magnetization state of the magnetic core and then convert it into an electrical signal. This simplified design reduces the number of components required and lowers the complexity of signal processing, thus usually having a lower production cost.Even though open-loop flux gate sensors are not too expensive, their cost is still relatively high. For instance, a low-cost open-loop flux gate current sensor might range from 50 to 200 RMB, while a high-performance open-loop flux gate sensor, which offers higher accuracy and a wider dynamic range, could cost between 500 and 2000 RMB or even more.

Open-loop flux gate sensors have potential for development. Technically, they feature low zero drift and temperature drift because the magnetic core is in an alternating B-H magnetic field, avoiding magnetic bias in the magnetic path. This makes them highly accurate for small current measurements, especially in terms of dynamic characteristics and high resolution.

Through Comsol simulation analysis, the key technology of the magnetic ring design for open-loop flux gate current sensors has been experimentally verified. The magnetic ring can increase the current measurement sensitivity by 15.4 times, with a frequency up to 6.7 kHz, meeting the requirements for complex AC and DC leakage current detection.

This means that open-loop flux gate sensors can be used to measure various AC, DC, pulse, and complex signals. They have a wide range of applications in industrial fields, such as drivers, power supplies, power supply fault detection, new energy, photovoltaic array side human contact protection, etc.

For example, the ±100A busbar current sensor reference design using open-loop flux gate sensors provides a non-invasive (isolated and lossless) current measurement solution up to ±100A, suitable for applications such as BMS, AC driver control modules, servo driver control modules, etc.

Currently, there are also many companies in the market that have launched corresponding flux gate sensor products. For example, TI's TIPD205 reference design uses an open-loop flux gate sensor to accurately measure DC, AC, and pulse currents up to 100A. The DRV425 is a flux gate magnetic field sensor designed specifically for single-axis magnetic field sensing, suitable for electrically isolated high-sensitivity precision DC and AC magnetic field measurement. This sensor has low offset, low drift, and low noise characteristics, and is widely used in fields such as busbar current sensing, wiring current sensing, solar inverters, etc.

There is also the LEM CAB series flux gate current sensor, designed specifically for current measurement in battery packs of electric and hybrid vehicles. For example, the CAB-SF 1500-001 model, with a rated value of 1500A and a measurement range of 1500A, is suitable for open-loop flux gate applications and features high accuracy and a wide temperature range.

Domestic open-loop flux gate products are still in the development stage. The good news is that Fuzhou IoT Open Lab released 12 models of three series of self-developed C01/C02/C03 flux gate current sensors at the end of 2023. This marks China's realization of domestic substitution in the field of flux gate sensors, breaking away from dependence on imported products, and building an independent, controllable, and secure domestic production and supply system.

In addition, Xinjin Electronics launched the first domestic developed and mass-produced flux gate high-precision closed-loop current sensor IC CC6836 in 2024. Although this is a closed-loop version, it also reflects the progress and maturity of domestic enterprises in flux gate sensor technology.The performance of open-loop magnetic flux gate sensors in terms of accuracy, temperature drift, bandwidth, and response time is increasingly valued. Their high precision and low drift characteristics give them great potential in the field of high-precision measurement. With the development of electric vehicles and energy storage technology, there is indeed a growing market demand for high-precision, high-reliability current measurement, which provides a potential growth opportunity for open-loop magnetic flux gate sensors. However, to truly become mainstream in the market, they still need to continuously prove their value in practical applications and demonstrate a clear competitive advantage over traditional sensors.

In summary, relying on a simpler design and relatively lower cost compared to closed-loop magnetic flux gate sensors, coupled with their high precision, low drift, and high sensitivity characteristics, if they can also meet the huge demand for high-precision, high-stability, and high-efficiency current sensors in electric vehicles, energy storage systems, renewable energy, and automation fields, then the future of open-loop magnetic flux gate sensors is promising.