Recommended SMT alloy resistors: Yineng EMA series
Surface Mount Alloy Resistors are surface mount resistors made of alloy materials such as manganese copper, nickel chromium, iron chromium aluminum, etc. They have the characteristics of low resistance, high precision, low temperature drift, and high power carrying capacity. They are designed specifically for current detection, power distribution, and high reliability scenarios. The following is a detailed analysis of its technical principles, core advantages, and typical applications:
1、 Basic Definition and Material Characteristics
Core concepts
Alloy material: resistance body is made of metal alloy (such as manganese copper NiCr, constantan, iron chromium aluminum FeCrAl), which has low resistivity, high stability and anti-aging characteristics.
Surface mount packaging: Using standard surface mount (SMD) packaging (such as 0805, 1206, 2512, etc.), it facilitates automated production and high-density PCB layout.
Material advantages
Low resistivity: The resistivity of alloy materials is usually 10100 Ω· cm, which is 1-2 orders of magnitude lower than conventional thick film resistors and suitable for manufacturing milliohm level low resistance resistors.
Low temperature drift coefficient (TCR): TCR can be as low as ± 15ppm/℃, significantly better than thick film resistors (± 200~± 500ppm/℃).
Resistance to vulcanization and corrosion: Alloy materials are naturally resistant to vulcanization, combined with epoxy coatings or ceramic substrates, suitable for humid and corrosive environments.
2、 Structure and Technical Characteristics
Core structure design
Alloy resistance layer: Precision resistors are formed through sputtering, etching, or stamping processes.
Copper terminals and electrodes: Nickel/tin or gold plated copper terminals are used to reduce contact resistance and thermoelectric potential (EMF).
Kelvin connection: Some models support a four pin design, separating the current path and voltage detection path to improve sampling accuracy (such as the Wangquan LRE series).
Key performance parameters
Resistance range: Typical values are 1m Ω~100m Ω (such as 2m Ω~19m Ω for the Wangquan RN series).
Accuracy: ± 0.1%~± 1%, high-precision models can reach ± 0.05%.
Rated power: 1W~5W (surface mount packaging), with improved heat dissipation capability through wide electrodes or metal substrates.
Temperature range: 55 ℃~+155 ℃, meeting the requirements of automotive grade working environment.
3、 Core advantages
High precision and low-temperature drift
The stable molecular structure of alloy materials ensures minimal changes in resistance with temperature, making them suitable for precision current detection (such as BMS in new energy vehicles).
Low thermal electromotive force (EMF)
The matching design between copper terminals and alloy resistors reduces parasitic voltage caused by temperature differences (typical EMF<1 μ V/℃).
High power density
By optimizing the heat dissipation design (such as large-area electrodes and ceramic substrates), surface mount packaging can carry higher currents (such as 2512 package support) 5W@25 ℃).
Resistance to mechanical stress and long lifespan
Alloy materials are resistant to vibration and impact, certified by AECQ200, and suitable for high reliability scenarios such as automotive electronics.
4、 Typical application scenarios
New energy vehicles
Battery Management System (BMS): detects battery charging and discharging currents, achieves SOC estimation and overcurrent protection (such as the Wangquan RN series).
Motor driver: Real time monitoring of motor phase current and optimization of control algorithms (such as FOC vector control).
Industrial power and energy systems
DCDC converter: Output current sampling, achieving closed-loop voltage regulation and overload protection.
Photovoltaic inverter: DC side current detection to improve MPPT efficiency.
Consumer Electronics
Fast charging device: Current detection in USB PD protocol ensures safe charging.
Smart home appliances: current monitoring of motor drive circuits (such as air conditioning compressors).
5、 Selection and Design Points
Matching resistance and power
Formula calculation: Select the resistance value (R=V_sense/I2) based on the maximum current (I2), and ensure that the power P=I ² R ≤ 70% of the rated power (derating design).
Example: When detecting 50A current, a 1m Ω resistor with a voltage drop of 0.05V and a power consumption of 2.5W should be selected, and a model with a rated power of ≥ 3.5W should be chosen.
Packaging and heat dissipation optimization
Surface mount packaging: 0805/1206 is suitable for compact spaces, 2512/3720 is suitable for high-power scenarios.
PCB design: Large area copper plating, adding heat dissipation vias to reduce the impact of temperature rise on accuracy.
Signal chain design
Differential amplifier: requires high common mode rejection ratio (CMRR>100dB) to suppress noise.
Filter circuit: Parallel 0.1 μ F ceramic capacitors are used to filter out high-frequency interference (such as switch power supply noise).
6、 Example of RALEC surface mount alloy resistors
LRE series (automotive grade)
Resistance range: 2m Ω~100m Ω, accuracy ± 0.5%, TCR ± 50ppm/℃.
Package: 0805/1206, supports four wire connection, anti sulfurization design.
Application: BMS current detection, on-board DCDC converter.
RN series (high power)
Features: 2512 package, power 3W@70 ℃, resistance as low as 2m Ω, in compliance with AECQ200 standard.
7、 Common Problems and Solutions
Temperature rise causes resistance drift
Optimize heat dissipation design (such as adding heat dissipation pads), or choose models with lower TCR (such as ± 15ppm/℃).
The sampling signal has high noise
Adopt differential routing and parallel RC low-pass filter (such as 10 Ω+1nF) at the sampling end.
Resistance deviation after welding
To avoid prolonged high-temperature welding time, it is recommended to use reflow soldering technology and choose high-temperature resistant alloy materials.
Surface mount alloy resistors, with alloy materials and precision manufacturing processes as their core, have become key components for high-precision current detection and high current power control. Its low resistance, low temperature drift, and high reliability make it irreplaceable in fields such as automotive electronics, new energy, and industrial power supplies. When selecting, special attention should be paid to the accuracy of resistance values TCR、 Optimize heat dissipation and signal chain design based on power margin and environmental adaptability, combined with system requirements, to achieve optimal performance and lifespan.