Deep Analysis of Precision Resistors
Precision resistors are a type of resistor with extremely high precision, low temperature coefficient (TCR), and long-term stability. Their core goal is to maintain high consistency in resistance values in complex environments (such as temperature, humidity, and time changes), meeting the strict requirements for circuit accuracy. Here is its comprehensive analysis:
1、 Basic Definition and Technical Characteristics
Core Features
High precision: The resistance tolerance is extremely small, with common levels of ± 0.1%, ± 0.05%, or even ± 0.01% (such as the Vishay Z1 series).
Low temperature coefficient (TCR): TCR is usually ± 1~± 50 ppm/° C (ordinary resistors are mostly ± 100~± 500 ppm/° C).
Long term stability: The resistance value changes very little during the life cycle (such as an annual drift rate of ≤ 0.01%).
Low noise and low inductance: Optimize structural design to reduce the impact of parasitic parameters on high-frequency circuits.
Materials and processes
Thin film technology: Metal alloys (such as nickel chromium and silicon chromium) are deposited on ceramic substrates through vacuum sputtering or evaporation processes, with precise thickness control (at the nanometer level) to achieve high precision.
Foil resistance technology (such as Vishay Bulk Metal) ® Coil: A special alloy foil is bonded to a substrate and a resistance pattern is formed through photolithography, with a TCR as low as ± 0.2 ppm/° C
Winding technology: using manganese copper or Evanohm alloy wire winding, combined with ceramic skeleton, with high precision but limited frequency characteristics.
2、 Main categories and typical products
|Type | Characteristics | Typical Models and Parameters | Application Scenarios|
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|Metal film precision resistor | Low cost, high cost-effectiveness, tolerance ± 0.1%~± 0.5%, TCR ± 10~± 50 ppm/° C. | Yageo RT series (0.1W~2W, ± 0.1%) | Industrial control, instrumentation|
|Metal foil precision resistor | Ultra high precision and stability, tolerance ± 0.001%, TCR ± 0.2~± 5 ppm/° C. | Vishay VHP100 (0.6W, ± 0.01%) | Metrology calibration, medical equipment|
|Precision wound resistor | resistant to high voltage and high power (up to 100W), but poor high-frequency performance with a tolerance of ± 0.01%~± 0.1%. | Ohmite D100K（50W， ± 0.1%) | Power calibration, power testing|
|SMT precision resistor | miniaturization design, tolerance ± 0.1%~± 0.5%, TCR ± 10~± 25 ppm/° C, supports high-density PCB. |Panasonic ERJ series (0402~2512, ± 0.1%) | Communication equipment, automotive electronics|
|Current detection resistor | Low resistance value (m Ω level), high accuracy (± 0.5%), high current resistance, temperature coefficient matching. |Isabellenh ü tte IVT Series (0.5m Ω, ± 0.5%) | Electric Vehicle BMS, Power Management|
3、 Core performance parameters
Accuracy level (tolerance)
Characterize the deviation range between the nominal resistance value and the actual value, such as ± 0.1% indicating that the actual resistance value fluctuates within ± 0.1% of the nominal value.
Temperature coefficient (TCR)
Unit: ppm/° C (parts per million per degree Celsius).
Calculation formula:
\[
TCR = \frac{R_2 R_1}{R_1 \times (T_2 T_1)} \times 10^6
\]
Among them\ (R1) and (R2) are the resistance values at temperatures of (T1) and (T2).
Long term stability
The resistance change rate after 1000 hours of operation at rated power and temperature is usually ≤ 0.05%.
Load life
Resistance drift after continuous full load operation, such as ± (0.1%+0.005 Ω) (test conditions: 70 ℃/1000 hours).
4、 Typical application scenarios
Precision measuring instruments
The voltage divider/shunt network in multimeters and bridges ensures measurement accuracy (such as Fluke calibration equipment using Vishay foil resistors).
High precision ADC/DAC reference voltage circuit.
Medical Electronics
The signal conditioning circuit of electrocardiograph (ECG) and blood analyzer requires low noise and high stability.
Automotive Electronics
The sensor signal processing in the engine control unit (ECU) requires AECQ200 certification.
Current sampling of battery management system (BMS) (such as 0.5m Ω± 1% detection resistor).
Industrial automation
Analog input/output circuits in PLC modules.
Feedback control of robot servo drivers.
Aerospace
Anti radiation reinforced resistors for satellite communication equipment and flight control systems (such as TE Connectivity RN series).
5、 Selection and usage points
Key factors for selection
Accuracy requirement: Select the tolerance level (such as ± 0.1% or ± 0.01%) based on the circuit error budget.
Temperature range: In high temperature scenarios, a lower TCR resistance (such as TCR ± 5 ppm/° C) should be selected.
Power and packaging: The power of surface mount resistors is usually ≤ 2W, and for high-power requirements, winding or aluminum shell resistors can be selected.
Cost balance: Metal foil resistors have the best performance but are expensive, while metal film resistors offer better cost-effectiveness.
Design considerations
Thermal management: Avoid placing precision resistors near heat sources, and if necessary, use a symmetrical layout to reduce the impact of thermal gradients.
PCB layout: Shorten the wire length to reduce parasitic inductance, and use Kelvin connection for current detection resistors.
Aging pretreatment: Perform electrical aging on ultra-high precision resistors (such as 100 hours @ rated power) to stabilize the resistance value.
Failure prevention
Mechanical stress: Avoid PCB bending that may cause cracking of surface mount resistors (such as choosing anti vibration models for automotive electronics).
Moisture protection: Choose moisture-proof packaging (such as silicone coating or sealed shell) for high humidity environments.
6、 Comparison with ordinary resistors
|Characteristics | Precision Resistors | Ordinary Resistors|
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|Accuracy | ± 0.01%~± 0.5% | ± 1%~± 10%|
| TCR | ±1~±50 ppm/°C | ±100~±500 ppm/°C |
|Long term stability | ≤ 0.05% (annual drift) | ≤ 1%~5% (annual drift)|
|Cost | High (complex materials and processes) | Low (standardized production)|
|Typical Applications | Metrology, Medical, High Precision Control | Consumer Electronics, General Circuits|