LR Series Metal Alloy Low-Resistance Resistors
The LR Series is a range of lead-free, halogen-free, RoHS-compliant metal alloy low-resistance resistors in surface-mount format, designed for current sensing and power measurement in compact, high-precision electronic assemblies. Power ratings span 0.5W to 5W and resistance values cover 0.2mΩ to 300mΩ, with tolerance options of ±0.5%, ±1%, ±2%, and ±5%.
The series is offered across nine footprint sizes — 1206, 1210, 2010, 2512, 2512H (with integrated heat sink), 2725, 2728, 4527S (without heat sink), and 4527 — allowing the same electrical specification to be selected at the package size appropriate for the available board area and thermal dissipation requirement. The operating temperature range is −55°C to +170°C.
Temperature coefficient of resistance (TCR) varies by resistance value and package, ranging from ±25ppm/°C at higher resistance values in larger packages up to ±175ppm/°C in the sub-milliohm range of the 1206 package. The 2512H variant adds an integrated heat sink tab to the standard 2512 footprint, extending its usable power range for resistance values in the 10mΩ to 200mΩ band. All variants are qualified to JIS C5201 and MIL-STD environmental test methods and are supplied on tape and reel for automated placement.
What are the LR Series Metal Alloy Low-Resistance Resistors?
The LR Series consists of surface-mount current sensing resistors constructed from precision metal alloy elements. The metal alloy material provides the combination of low base resistance, stable TCR, and long-term resistance stability that distinguishes this class of component from thick-film alternatives, particularly in the sub-5mΩ range where thick-film processes struggle to maintain tight tolerance and low TCR simultaneously.
The two-terminal construction and standard SMD land patterns make the LR Series a direct drop-in for automated PCB assembly. Resistance values are laser-trimmed and marked on the component body using a standardised four-digit code — or a three-digit code for LR2512 values between 0.3mΩ and 4.0mΩ — where the letter ‘m’ denotes the decimal position in milliohms, allowing unambiguous identification of sub-milliohm values in production and inspection.
The nine available case sizes span a wide range of power and current-handling capability. The 1206 and 1210 packages address low-current sensing requirements in space-constrained designs at up to 2W. The 2010 and 2512 packages step up to higher current applications at 1W to 5W. The 2725 and 2728 packages offer wider body geometries that lower thermal resistance and enable stable measurement at resistance values down to 0.2mΩ and power levels up to 5W. The 4527 and 4527S packages provide the largest footprint in the series, rated at 5W, and are suited to high-current sensing in power conversion and battery management circuits. The 2512H variant supplements the standard 2512 with an integral heat sink element, lifting its effective power rating for the higher resistance values in that package where the limiting factor is element self-heating rather than terminal current capacity.
Environmental qualifications cover the full range of PCB manufacturing and field stresses: solder heat resistance at 260°C, solderability at 245°C, 1000-hour high-temperature storage at +170°C, 1000-hour low-temperature storage at −55°C, 1000-cycle temperature cycling from −55°C to +150°C, bias humidity at 85°C and 85% RH, vibration from 10Hz to 55Hz, and a 1000-hour load life test at rated power. Short-time overload is specified at five times rated power for five seconds, with resistance change not exceeding ±0.5% for all types except the 4527 and 4527S, which are rated to ±2%.
LR Series Metal Alloy Low-Resistance Resistors Specifications
A practical overview for engineers and procurement teams evaluating resistive solutions.
Model: LR
Resistor type: Metal alloy
Description: Low resistance
Power Rating: 0.5W~5W
Resistance (Ω): 0.2m~300m
Tolerance (%): ±0.5, ±1, ±2, ±5
TCR (ppm/C): 25-175
Applications of the LR Series Metal Alloy Low-Resistance Resistors
Where RARA metal clad resistors are deployed in the field.
Power supply current sensing — measuring output or input current in switched-mode and linear power supplies for closed-loop regulation, overcurrent protection, and efficiency monitoring.
Battery pack management — charge and discharge current measurement in lithium-ion, NiMH, and lead-acid battery systems for state-of-charge estimation and protection circuit operation.
LED driver circuits — output current sensing in constant-current LED drivers for luminous flux regulation and thermal protection.
Measuring instruments and precision test equipment — shunt resistors in current meters, power analysers, and data acquisition systems where stable, low-TCR elements are required for accuracy over temperature.
Motor drive and variable-speed drive circuits — phase current sensing in inverter and H-bridge stages for torque control, overcurrent detection, and short-circuit protection.
DC-DC converters and voltage regulators — current sensing in synchronous buck, boost, and buck-boost topologies for peak current mode control and load current monitoring.
Automotive electronics — current sensing in on-board chargers, DC-DC converters, and body electronics modules in applications requiring RoHS and halogen-free compliance.
Portable and handheld devices — compact current sensing in smartphones, tablets, and wearables where the 1206 and 1210 footprints provide the smallest available metal alloy shunt in a standard SMD outline.
Industrial automation and control — current feedback in servo drives, programmable logic controllers, and field device power circuits requiring stable measurement across wide ambient temperature ranges.
Related Products of the LR Series Metal Alloy Low-Resistance Resistors
Model: MFF
Resistor type: Metal foil
Description: Low resistance chip
Power Rating: 0.33W~4W
Resistance (Ω): 0.5m~100m
Tolerance (%): ±0.3, ±0.5, ±1
TCR (ppm/C): 30-100
Model: LR2512H
Resistor type: Metal alloy
Description: Low resistance
Power Rating: 2W~3W
Rated Current: 17.3A
Resistance (Ω): 10m~80m
Tolerance (%): ±1, ±2, ±5
TCR (ppm/C): 50
Model: LRE
Resistor type: Metal alloy
Description: Low resistance
Power Rating: 1/6W~1W
Resistance (Ω): 0.2m~300m
Tolerance (%): ±0.5, ±1, ±2, ±5
TCR (ppm/C): 1-175
Model: MR
Resistor type: Metal alloy
Description: Low resistance
Power Rating: 2W, 3W, 5W
Resistance (Ω): 4m~100m
Tolerance (%): ±1, ±2, ±5
TCR (ppm/C): 50, 75, 200
Why Choose RARA Current Sensing Resistors
What sets RARA apart for engineers and procurement managers in industrial and automotive markets.
01
8 Sub-Categories
No other single supplier covers AEC-Q200 chip shunts, milliohm precision types, four-terminal Kelvin shunts, power metering, and 12,000A panel shunts under one ISO-certified roof.
02
Extreme Precision
HPS, UHPS, and PSS precision shunts deliver ±0.05% tolerance and 3 ppm/°C TCR — meeting the accuracy demands of EV battery coulomb counting, precision power analyzers, and billing-grade energy metering.
03
Automotive Qualified
Multiple AEC-Q200 certified models (BCS, LRA, ECS, BWR, TCS, PCBS) with IATF 16949 manufacturing certification — covering EV battery management, motor control, and charging applications.
04
Global Track Record
Trusted by Tesla, GM Korea, Proterra, Siemens, Rockwell, and Schneider Electric — deployed in EV powertrains, industrial drives, and utility metering systems across six continents.
