Current Sense Resistor Calculator

A current sense resistor (also called a shunt resistor) is a small resistor placed in a circuit to measure current by producing a proportional voltage drop — the Current Sense Resistor Calculator works out the exact resistance value you need. Enter your Maximum Current, Desired Sense Voltage, and Supply Voltage to get the required Shunt Resistance. Secondary outputs include Power Dissipation, Recommended Power Rating (based on your chosen derating factor), Voltage Drop, and Sensitivity in mV/A.

A

The maximum current you need to measure

V

The voltage you want across the shunt at maximum current

V

The circuit supply voltage

ppm/°C

Temperature coefficient for accuracy calculations (optional)

°C

Temperature variation from ambient

Safety factor for power rating selection

Results

Shunt Resistance

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Power Dissipation

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Recommended Power Rating

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Voltage Drop

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Sensitivity

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Frequently Asked Questions

What is the optimal sense voltage for a current sense resistor?

The optimal sense voltage is typically between 50mV and 200mV. Lower voltages minimize power loss but reduce signal-to-noise ratio, while higher voltages provide better accuracy but waste more power. 100mV is a common compromise.

How do I account for temperature effects in current sensing?

Temperature affects resistor value through its temperature coefficient (TCR). Use precision resistors with low TCR (typically <100ppm/°C) for critical applications. The calculator considers temperature coefficient to estimate accuracy drift over your operating range.

What power rating should I choose for my shunt resistor?

Choose a power rating 2-10 times higher than the calculated dissipation to avoid overheating and ensure reliability. The calculator recommends a safety factor - use higher factors for critical applications or harsh environments.

Can I use multiple shunt resistors in parallel to increase power handling?

Yes, parallel resistors can increase power handling capability, but they must be well-matched in value and temperature coefficient. The total resistance equals 1/(1/R1 + 1/R2 + ...) and power is distributed among them.

How do I minimize noise in current sense measurements?

Use larger sense voltages when possible, add filtering capacitors across the sense resistor, use differential amplifiers, implement Kelvin connections for precision, and keep sense traces short and away from switching circuits.

What's the difference between current sense resistors and regular resistors?

Current sense resistors are precision devices with tight tolerances (±1% or better), low temperature coefficients, and often four-terminal Kelvin connections. They're designed specifically for measurement applications where accuracy is critical.

How does voltage drop affect my circuit performance?

The voltage drop across the shunt resistor reduces available voltage for your load. Keep this under 1-2% of supply voltage for most applications. Higher drops waste power and may affect circuit regulation.

What are typical applications for current sense resistors?

Current sense resistors are used in power supplies, battery management systems, motor controls, LED drivers, and anywhere precise current monitoring is needed for protection, regulation, or measurement purposes.