Current Sensor Types: Shunt, Hall Effect, and Current Transformer Comparison

A current sensor turns current flowing through a conductor into a signal a circuit can measure. That signal might be a small voltage across a resistor, an output proportional to a magnetic field, or the secondary current of a transformer.

The best type of current sensor depends on the job. A battery monitor must measure DC efficiently. A motor controller may need fast, bidirectional measurements. A mains-current monitor may prioritize isolation. Accuracy, heat, bandwidth, board space, and cost then determine which implementation makes sense. Three common starting points are a shunt resistor, a Hall-effect sensor, and a current transformer (CT).

How Does Current Sensing Work?

Every method observes an effect caused by current:

1. Shunt sensing places a known, low-value resistance in the current path and measures the voltage across it.
2. Magnetic sensing measures the field around a current-carrying conductor. Hall-effect sensors are a common example.
3. Transformer sensing uses changing magnetic flux from an AC conductor to induce a measurable secondary current.

The sensor must measure the section of the conductor whose current you actually want to know. For a single supply feeding several branches, a sensor at the input to the branches indicates a combined current. On the other hand, a sensor located on one branch reports only the current flow within the one branch.

Compare candidate specifications of current sensors using the terminology below:

• Measurement range: The span of current the sensor is designed to measure.
• Sensitivity: How much the sensor’s output changes per ampere of measured current.
• Accuracy: How closely the reported value corresponds to the actual current under specified conditions.
• Offset: The sensor output or apparent current when the actual current is zero.
• Bandwidth: The range of signal frequencies the sensor can measure accurately.
• Response time: How quickly the sensor output responds to a change in current.
• Insertion resistance and power loss: For sensors that place a sensing element in the current path, the added resistance causes voltage drop and power dissipation. Lower values generally reduce the sensor’s effect on the circuit.
• Galvanic isolation: Electrical separation between the measured circuit and the measurement electronics, with no direct conductive path between them.

Shunt Resistor Current Sensors

A shunt is a precision resistor placed in series with the current you want to measure. By Ohm’s law:

V_SHUNT = I × R_SHUNT
P_SHUNT = I² × R_SHUNT

The first equation gives the signal available to measure. The second gives the heat dissipated in the resistor. Suppose 2 A flows through a 0.05 Ω shunt: it develops 0.1 V and dissipates 0.2 W. The power rating must allow for operating temperature and margin, not merely match that calculated value.

A smaller shunt reduces voltage drop and heat but also produces a smaller measurement signal. That makes amplifier offset, electrical noise, trace resistance, and ADC resolution more important. In contrast, a larger shunt generates a voltage value that is easier to read but wastes more power. The right value balances both effects across the full current range.

Most practical designs use a current-sense amplifier or monitor IC to measure and amplify the small differential voltage across the shunt resistor. Check the amplifier’s common-mode range, input offset, gain error, bandwidth, and whether it supports current in one or both directions. Shunt tolerance and temperature coefficient also contribute to measurement error.

Low-side sensing puts the shunt in the return path (after the load). Because the voltage across the shunt is measured close to circuit ground, the measurement circuitry can be simpler. The drawback is that the load ground rises above system ground by the shunt’s voltage drop; low-side sensing can also miss some load-to-ground faults.

High-side sensing puts the shunt between the supply and load. It preserves the load’s ground reference and can reveal certain ground-short faults, but the amplifier must tolerate the supply’s input common-mode voltage. Texas Instruments’ high- and low-side guidance explains this trade-off.

For accurate PCB measurement, use Kelvin connections: separate, closely routed sense traces from the high-current copper carrying the load. A four-terminal shunt makes this especially clear. Otherwise, the voltage drop in pads and power traces can become part of the reading. Analog Devices’ reference design highlights this layout requirement.

A four-terminal shunt typically has four connections:

• Current input (I+): Carries load current into the shunt.
• Current output (I−): Carries load current out of the shunt.
• Sense positive (S+): Provides the voltage measurement point on the positive side of the resistive element.
• Sense negative (S−): Provides the voltage measurement point on the negative side of the resistive element.

Note: A shunt-based current sensor does not measure current directly. The measurement circuitry measures the small voltage drop between S+ and S− and calculates the current using the shunt’s known resistance (I = V/R).

Because the sense terminals are separate from the high-current terminals, voltage drops in PCB traces, solder joints, and terminal contacts are largely excluded from the measurement.

Shunts are often attractive for cost-sensitive DC or AC measurements where a small voltage drop is acceptable. They do not provide inherent galvanic isolation, meaning there is a direct electrical connection between the measured circuit and the measurement circuitry. If electrical separation is required (e.g., to protect low-voltage electronics from a high-voltage circuit), additional isolation circuitry is needed. Such isolation circuitry can include an isolation amplifier or isolated ADC, often together with an isolated power supply and an isolated digital interface.

Hall Effect and Magnetic Current Sensors

Current flowing through a conductor creates a magnetic field around it. A Hall-effect current sensor measures this field and produces an electrical output, typically a voltage proportional to the instantaneous current.

Hall-effect sensors can measure both DC and AC current. With DC, the output settles at a level corresponding to the magnitude and direction of the current. With AC, the output varies over time as the current changes magnitude and direction. Then, measurement circuitry can use this signal to determine values such as instantaneous, peak, or RMS current.

A current transformer (CT) also measures current through its magnetic field, but uses transformer action: changing current in the primary conductor induces a current or voltage in a secondary winding. Because this requires a changing magnetic field, a conventional CT measures AC but not steady DC. This ability to measure DC as well as AC is a key difference between Hall-effect sensors and conventional CTs.

There are several implementations of Hall-effect sensors.

• An open-loop Hall sensor measures the magnetic field produced by the current directly. It is comparatively simple and typically requires less power and cost.
• A closed-loop Hall sensor uses a compensation winding to generate a magnetic field that opposes the field produced by the measured current. Measuring the current required to create this opposing field can improve accuracy, linearity, and response, but generally adds size, power consumption, and cost.

Then, independently, Hall-effect sensors can be integrated or discrete, and core or coreless.

• Integrated vs. discrete: An integrated Hall sensor IC combines the current-carrying conductor, Hall element, and measurement electronics in a single package, simplifying PCB integration. A discrete implementation uses separate components, which can provide greater flexibility in conductor geometry, sensing range, and physical arrangement.
• Core-based vs. coreless: A core-based Hall sensor uses a magnetic core or concentrator to direct and strengthen the magnetic field at the Hall element. A coreless sensor measures the field without a large magnetic core, which can reduce size and weight but requires a design capable of accurately sensing the weaker, less concentrated field.

Beyond architecture, consider how the sensing method affects the current path and power loss. A magnetic sensor can reduce insertion loss compared with a shunt, especially at higher current, because the current path need not rely on a deliberately resistive element. It is not lossless: an integrated package has conductor resistance, so check its current rating, temperature rise, and board-copper requirements.

Hall-effect sensors can be particularly useful for motor phases, battery paths, and bidirectional current. Some devices provide galvanic isolation between the high-current conductor and the low-voltage output, but do not assume every Hall sensor is safety-rated for isolation. Check the specific device’s working voltage, insulation rating, clearance, and certification. TI’s Hall-effect current-sensor documentation shows that isolation and bandwidth differ among devices.

Offset, noise, sensitivity drift, and ambient temperature also matter. A sensor suitable for tens of amperes may have too much zero-current uncertainty for a few-milliamp measurement. Compare accuracy at the current you care about, not only the full-scale rating, and decide whether the system can perform a zero-current calibration.

Current Transformers and Other AC Current Sensors

A conventional current transformer (CT) surrounds or includes a conductor carrying AC. That conductor acts as the primary winding; changing magnetic flux induces current in the CT’s secondary winding. The secondary signal is related to the primary current by the turns ratio and is typically measured through a specified burden resistor.

The CT does not need to insert a resistor into the main current path and can provide galvanic isolation. This makes CTs useful for AC energy monitoring and mains-current measurement. A conventional CT cannot measure steady DC: without changing flux, it does not produce a continuing secondary signal. Its usable frequency range, phase error, core saturation, turns ratio, and burden all affect the measurement.

CT safety needs deliberate attention. An energized CT secondary must not be casually left open: hazardous voltage can develop across its terminals. Follow the manufacturer’s burden, termination, and service procedures. Schneider Electric’s CT guidance and ABB’s installation instructions both warn about open-secondary operation. Mains designs require qualified review against the applicable safety requirements.

Other magnetic technologies can be useful in narrower cases.

• A Rogowski coil senses changing current and uses an integrator to recover the waveform. It suits some high-current AC measurements but not steady DC.
• Fluxgate sensors can provide precise DC-capable magnetic measurement at greater complexity.
• Magnetoresistive sensors offer another way to measure field changes. These are worth evaluating when the main three options fail a particular accuracy, range, size, or bandwidth requirement.

How to Choose a Current Sensor for Your Design

Use the comparison below to shortlist technologies, then compare actual parts and reference circuits. Performance varies substantially within each category.

Current Sensing: Shunt resistor vs. Hall-Effect Sensor vs. Current Transformer

• For monitoring the current from a battery (battery monitoring), start with a shunt and a low-power monitor when precision and board space matter, then compare it with a Hall option if isolation or higher current changes the trade-off.
• For motor control, bandwidth, bidirectional operation, switching noise, and fault response may matter more than lowest component cost.
• For power supplies and voltage-regulator systems, current sensing can serve several purposes. It may provide feedback for regulating the output, report current consumption for monitoring or telemetry, or detect excessive current so the circuit can limit or shut down the output. These functions place different demands on the sensor: protection generally requires a fast response, while telemetry may prioritize measurement accuracy over speed.
• For solar and energy systems, separate DC-bus measurement from AC-output measurement before choosing a sensor.
• For mains-current monitoring, a suitably rated CT may be attractive, but its burden and open-secondary protection require careful design.
• For industrial equipment, consider using an isolated Hall solution where DC measurement and separation from a high-energy conductor are both required.

These are starting points, not universal recommendations.

The current sensor does not operate independently of its PCB layout. Because current measurement often involves small voltages, high-current paths, or magnetic fields, PCB routing and component placement can directly affect measurement accuracy, thermal performance, and electrical safety.

On the PCB, keep low-level measurement traces short and away from noisy switching nodes. Route Kelvin sense connections independently of the high-current path. Size copper and connectors for the full operating and fault conditions, account for shunt or package heating, and maintain the required isolation and creepage distances. Follow the selected manufacturer’s reference layout rather than improvising around a sensitive analog front end. Our PCB routing guide covers related layout fundamentals.

In Flux, you can compare candidate components, draw the shunt, Hall, or CT signal chain in the schematic editor, and review how the measurement path enters the PCB layout. Keep the current range, isolation target, thermal assumptions, and calibration plan beside the design so reviewers can judge the circuit against its real requirements.

FAQs

What are the main current sensor types?

What is the most accurate way to measure current?

Shunt versus Hall effect: what is the key difference?

Can a Hall-effect sensor measure DC?

Can a current transformer measure DC?

High-side versus low-side sensing?

How do you select a shunt?

Which current sensor provides galvanic isolation?