What Is a Shunt / Current Sense Resistor?
A shunt resistor (current sense) is a special, very low-value (usually milliohm-level) resistor used to measure the current flowing through a circuit.
How Does It Work?
The current flows through the shunt and drops a small voltage across it: V = I × R. By measuring this voltage we calculate the current indirectly.
Why Such a Low Value?
| Goal | Reason |
|---|---|
| Low resistance | Affects the circuit little (low voltage loss) |
| Low power loss | Little heating |
| Accurate reading | The small voltage is read with an amplifier |
Where Is It Used?
To monitor current in battery-charging circuits, motor drives, power supplies and overcurrent protection circuits.
Material and Stability
Shunt resistors are made of special alloys (e.g. manganin) whose value changes very little with temperature. Because the accuracy of the current measurement depends directly on the resistor's stability; a resistor whose value drifts when it heats up gives a wrong current reading.
Common Mistakes
- Choosing too high a value: causes needless voltage loss and heating in the circuit.
- Skipping the Kelvin connection: a 4-terminal (Kelvin) connection is essential for precise measurement.
- Forgetting the power rating: at high current even a small resistor dissipates significant power.
Frequently Asked Questions
Why is a shunt resistor at the milliohm level?+
What is a Kelvin connection?+
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