Current Sensing Beyond Shunt Resistors for Modern Electronics

Accurate current sensing is crucial in modern electronic systems, from electric vehicles to industrial robots. It enables efficient power management, precise motor control, overcurrent protection, and robust battery monitoring. For decades, shunt resistors have been the primary current measurement solution, using Ohm's Law to convert current into a measurable voltage drop. While shunt resistors are straightforward and cost-effective for basic applications, the increasing demands of high-performance, high-efficiency, and safety-critical systems highlight their inherent limitations.

Limitations of Shunt Resistors

Shunt resistors operate by inserting a small, known resistance into the current path, measuring the voltage drop, and calculating the current. This straightforward method has several drawbacks. Any resistance in the current path dissipates power as heat. In high-current applications, this power loss can be substantial, causing energy inefficiency and requiring robust thermal management. Heat can also cause resistance drift, affecting accuracy.

Shunt resistors lack electrical isolation between the high-current path and low-voltage measurement circuitry. This requires additional, often costly, isolation components like opto-isolators or isolation amplifiers, increasing bill-of-materials (BOM), board space, and design complexity, especially in high-voltage systems where safety is critical. The small voltage signals from shunts often need significant amplification, making them susceptible to noise. Maintaining high accuracy across wide temperature ranges and varying current levels is challenging due to temperature-induced voltage generation. For higher currents, shunts become physically larger to manage power dissipation, consuming valuable board space in compact designs. Finally, in applications with fast switching transients (high dV/dt), parasitic inductance can cause measurement inaccuracies and ringing. These limitations indicate a need for alternative current sensing technologies that offer better performance, integration, and efficiency.

Hall-Effect Current Sensors: An Alternative

Hall-effect current sensors offer an alternative to shunts which combine performance and integration. These sensors operate on the principle that a current-carrying conductor produces a magnetic field proportional to the current. A Hall element in this field generates a voltage proportional to the magnetic field strength, and thus, to the current. A primary advantage is galvanic isolation, as the Hall element is electrically separate from the current path. This isolation simplifies design, reduces component count, and enhances safety in high-voltage applications.

Modern Hall-effect current sensors address many shunt drawbacks by providing integrated solutions. For automotive applications needing high accuracy and fast response in noisy environments, the ACS71240 uses differential Hall sensing to reject common-mode magnetic fields, an improvement over shunts susceptible to external magnetic interference. The ACS71240 provides overcurrent fault detection in 1.5 µs, offering protection that often requires complex additional circuitry with shunts.

For higher current applications needing high efficiency and robust inrush current capability, the ACS37220 features ultra-low primary conductor resistance (less than 100 μΩ). This significantly reduces power dissipation and heat generation compared to high-power shunts, leading to higher system efficiency and less need for bulky thermal management. Its integrated features, including temperature compensation and a configurable overcurrent fault output, simplify system design and enhance reliability. This is particularly beneficial in automotive environments like battery management systems and motor control, where shunt-based solutions would create significant thermal challenges and complexity.

Allegro also offers the ACS37041 and ACS37042, small, integrated current sensors for cost-optimized and space-constrained applications. These devices provide a galvanically isolated voltage output (100 VRMS functional for ACS37041, 285 VRMS basic for ACS37042), removing the external isolation components shunts require in high-voltage systems. Their low 1.6 mΩ conductor resistance minimizes power dissipation, a key advantage over lossy shunt resistors in low-power designs. These sensors can sense bidirectional currents up to 30 A with a 125 kHz bandwidth and come in a compact 5-pin SOT23-W package. This integration streamlines design and enhances reliability by reducing the need for multiple external components.

These examples show how magnetic current sensors, with their galvanic isolation, reduced power loss, improved noise performance, faster response times, and integrated packages, address the limitations of traditional shunt resistors.

Current Sensing: Efficiency, Precision, and Safety

As e-mobility, energy infrastructure, automation, and robotics expand, advanced current sensing technologies will become increasingly important. The move from traditional shunt resistors is driven by the need for greater efficiency, higher accuracy, enhanced safety, and more compact designs. Magnetic current sensing solutions, especially Hall-effect-based sensors, offer advantages that meet these needs. These capabilities allow engineers to design more efficient, reliable, and safer systems in power electronics and control. Adopting these alternatives helps the industry optimize current measurements, achieve new levels of performance and support the next generation of intelligent and sustainable technologies.

For more information on how magnetic current sensors can improve designs and replace traditional shunt resistors, visit: https://www.allegromicro.com/en/products/emerging-technologies/replace-the-shunt