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Current sensing is one of the most common measurement tasks in power electronics, yet there is no single best method. Shunt resistors, current transformers and Hall effect sensors each measure current in a different way, and each has a completely different profile of cost, accuracy, isolation and bandwidth. Choosing the wrong method means either overpaying, losing accuracy, or discovering a safety problem only at the certification stage.
This article compares the three mainstream current sensing technologies and gives a practical framework for choosing the right one.
Why Accurate Current Sensing Matters
Current measurement is used for:
- Overcurrent and short-circuit protection
- Closed-loop current control in motor drives and power converters
- Power and energy metering
- Battery charging and state-of-charge estimation
- Fault detection and diagnostics
- Power factor and efficiency monitoring
The required accuracy, isolation and response speed differ for every one of these tasks — which is exactly why the sensing technology must be matched to the application.
The Three Technologies at a Glance
Shunt Resistors
A shunt resistor converts current into a small voltage drop, which is measured by an amplifier or an isolated amplifier. The voltage is proportional to the current via Ohm’s law: V = I × R.
- Measures both AC and DC
- Very low cost and small size
- Very wide bandwidth
- No galvanic isolation — the measurement circuit is at the rail voltage
- Dissipates power proportional to I² × R, so it is inefficient at high current
- Accuracy depends on resistor tolerance, temperature coefficient and the amplifier offset
Shunts are the natural choice for low-current, cost-sensitive designs where isolation is not required — for example, low-side current sensing in DC-DC converters.
Current Transformers (CTs)
A current transformer is a magnetic component: the measured conductor forms the primary (often a single turn), and a multi-turn secondary drives a burden resistor. The secondary current is a fixed ratio of the primary current.
- Measures AC only (no DC component)
- Inherent galvanic isolation
- Low insertion loss — no resistive drop in the primary path
- Capable of very high currents
- Bandwidth covers mains frequencies and well beyond, depending on the core
- Saturation limits accuracy at very high fault currents and DC bias
CTs excel in AC power metering, protection, and high-current AC applications where isolation and efficiency matter more than DC capability.
Hall Effect Sensors
Hall effect sensors measure the magnetic field produced by the current, either directly around a conductor or inside a magnetic core, and convert it to a proportional output voltage or current signal.
- Measures both AC and DC, including DC offset and mixed waveforms
- Inherent galvanic isolation
- Two families:
- Open-loop sensors: the Hall element output is amplified directly. Simpler and lower cost; accuracy is affected by the core and amplifier drift.
- Closed-loop (compensated) sensors: a secondary winding cancels the primary field with a feedback current. Higher accuracy and better linearity, lower temperature drift, higher cost.
- Wide bandwidth (DC to hundreds of kHz for many parts)
- No insertion loss in the primary path
Hall effect sensors are the standard choice for motor drives, EV traction, battery systems and any application that needs isolated DC-capable sensing with good accuracy.
Comparison Table
| Property | Shunt Resistor | Current Transformer | Hall Effect Sensor |
|---|---|---|---|
| Measures DC | Yes | No | Yes |
| Measures AC | Yes | Yes | Yes |
| Galvanic isolation | No | Yes | Yes |
| Insertion loss | I²R power loss | Very low | Very low |
| Bandwidth | Very wide | Wide (AC) | Wide (DC to ~hundreds kHz) |
| Accuracy (typical) | High (needs precision amp) | Good | Open-loop: moderate; Closed-loop: high |
| Linearity | Very good | Good | Open-loop: good; Closed-loop: excellent |
| Cost | Low | Low–moderate | Moderate–high |
| Size at high current | Large (heat sink needed) | Moderate | Moderate–small |
| Typical use | Low-side sensing, DC-DC converters | AC metering, protection | Motor drives, EV, battery, inverters |
Choosing by Application
Motor drives and servo drives — need DC-capable, isolated, wide-bandwidth sensing with fast overload response. Use Hall effect sensors (closed-loop for high accuracy, open-loop for cost-sensitive drives).
EV traction and battery management — DC plus high fault currents, galvanic isolation and thermal robustness. Use Hall effect sensors, often closed-loop for the traction inverter and open-loop for battery monitoring.
AC power metering and energy monitoring — current is sinusoidal and can be very high. Use current transformers for cost and isolation; add a shunt-based approach where DC measurement or very low cost is required.
DC-DC converters and point-of-load modules — small currents, no isolation needed at low side, cost-critical. Use shunt resistors with an integrated amplifier.
Solar inverters and UPS systems — mixed AC/DC paths and high efficiency requirements. Use Hall effect sensors on the DC side and current transformers or Hall sensors on the AC side.
Protection and fault detection — needs fast response and robustness to faults. Current transformers handle high fault currents naturally; Hall effect sensors give fast DC-aware response; shunts need careful amplifier protection.
Custom Current Sensor Solutions from Sirui-Tech
Current sensing is only as good as the magnetic component at its heart. Shaanxi SiRui Technology Co., Ltd manufactures custom current transformers and current sensor magnetics — split-core and solid-core types, miniature PCB types, and zero-phase current transformers — with the core material, turns ratio and package matched to your measurement circuit.
With OEM & ODM support, free samples, 100% pre-shipment inspection and RoHS/REACH compliance, we help you get the sensing accuracy and isolation your design needs, at the cost your BOM can afford. Send us your requirements and we will recommend the right sensing solution.
FAQ
Can a current transformer measure DC current?
No. A current transformer only responds to changes in current. For DC or mixed AC/DC measurements, use a Hall effect sensor or a shunt resistor.
Why is a shunt not used at very high currents?
Power loss grows with the square of the current. At hundreds of amps, the shunt would need to dissipate large amounts of heat and its size and cost would become unreasonable — an isolated sensor with no insertion loss is usually better.
Open-loop or closed-loop Hall sensor?
Choose open-loop when cost and size dominate and moderate accuracy (a few percent) is acceptable. Choose closed-loop when you need high accuracy, low temperature drift and fast response for control loops.
Which method is best for a DC-DC converter under 5 A?
A low-side shunt with an integrated current sense amplifier is usually the most cost-effective, accurate and compact option when the converter has no isolation requirement.
About Shaanxi SiRui Technology Co., Ltd
Shaanxi SiRui Technology Co., Ltd (Sirui-Tech) is a professional magnetic components manufacturer specializing in electrical transformers, power inductors, current sensors and magnetic cores. We offer OEM & ODM services with free samples, fast lead times and 100% pre-shipment inspection. Browse our products or contact us for a quote.