Current-Sense Resistor

Also called a “shunt” in higher-current applications, the current-sense resistor remains the most accurate and cheapest way to measure DC and AC current from milliamps to thousands of amps. The value is chosen as a compromise: too low and the sense voltage drowns in noise and offset; too high and resistor dissipation P = I² × R becomes wasteful and the resistor heats up.

Key selection parameters are tolerance (often ±1 % or tighter), TCR (≤ 50 ppm/K to keep gain stable over temperature, with Manganin ≈ 15 ppm/K, Zeranin ≈ 5 ppm/K), thermal EMF (low thermal-couple voltage at the terminals), power rating (must accept I_max² × R continuously), and parasitic inductance (matters above 10 kHz). Four-wire Kelvin connections eliminate contact resistance errors at the sub-milliohm level.

Applications include over-current protection in switching power supplies, motor current control in inverters and servo drives, battery management systems for state-of-charge estimation, hot-swap controllers, and laboratory DMMs. For pulse current sensing in IGBT gate drivers and battery loads, low-inductance constructions (Kelvin shunts, four-terminal SMD, foil shunts) are mandatory. Datasheet “sense” parts from manufacturers reach ±0.1 % tolerance and ±2 ppm/K TCR for laboratory-grade measurement.