A carbon film fixed resistor produced by BEC is an entry-level passive electronic component with a non-adjustable resistance value, constructed by depositing a thin, uniform film of carbon (graphite) onto an insulating ceramic substrate. It is the most widely used and cost-effective film resistor type, designed for non-precision, low-to-moderate power, and mild-environment circuits where performance requirements are basic (e.g., general biasing, current limiting, switching). It trades off precision, thermal stability, and low noise for ultra-low cost and ease of manufacturing-making it a staple in consumer electronics, basic industrial circuits, and hobbyist projects.
Basic Parameters
|
Product Category |
Carbon film fixed resistor |
|
Resistance Range |
0.1Ω~100MΩ |
|
Rated Power |
1/6W~7W |
|
T/C |
±350ppm/℃~±1500ppm/℃ |
|
Tolerance |
±2%. ±5%, ±10% |
|
Certificate |
RoHS, REACH |
|
Applications |
Power supplies, telecom equipment, medical devices, industrial applications, consumer electronics |
Characteristics
Substrate: Low-to-medium purity alumina (Al₂O₃) ceramic (or carbon core for legacy variants) - provides basic electrical insulation and minimal thermal conductivity (only for low-power heat dissipation).
Resistive Layer: A thin (5–20μm) film of amorphous carbon/graphite deposited via thermal decomposition of hydrocarbon gas (e.g., methane) - the film's thickness and density set the base resistance; no expensive alloys or oxides are used.
Trimming: A helical groove is cut into the carbon film (mechanical trimming for 99% of grades, laser trimming for rare ±1% precision variants) to calibrate resistance to target tolerance-mechanical trimming is slower but far cheaper than laser.
Terminations: Basic nickel-copper or tin-plated steel end caps with no corrosion/barrier layers (a key cost cut) - fitted with axial lead wires (THT) (dominant form factor) or simple tin-plated solder contacts (SMD variants).
Protective Coating: Thin epoxy or phenolic resin coating (vs. glass/glass-epoxy for metal/metal oxide film) - shields the carbon film from minor dust/moisture but is permeable to humidity and low heat-resistant. Laser-printed resistance, tolerance, and power ratings are applied here (on THT variants).
Production Process
Parts of Our Production Facilities
FAQ
Q1: What tolerance and TCR values are standard for carbon film fixed resistors?
A1: Tolerance (precision) and TCR (Temperature Coefficient of Resistance) are cost
optimized-no tight-precision options (a deliberate tradeoff for low cost):
Tolerance
±5%: Standard grade (most widely used) - for basic circuits where small resistance variations don't matter.
±10%: Cost-optimized grade - for the cheapest non-critical circuits (e.g., disposable electronics).
±1%: Special order only (rare) - not cost-effective, as metal film resistors are a better choice for tight tolerance.
TCR: ±150 → ±600 ppm/°C (negative TCR is dominant) - poor thermal stability, meaning resistance shifts significantly with temperature (e.g., a 1kΩ resistor with ±300 ppm/°C changes by 0.3Ω over a 100°C temperature swing).
Q2: What is the maximum operating voltage for a carbon film fixed resistor?
A2: Moderate voltage capability (package/power-dependent), derated proportionally with current/power draw (no high-voltage specialized grades):100V (1/8W) → 500V (5W) - suitable for low-to-moderate voltage basic circuits (e.g., 12V/24V consumer/industrial control).
Q3: Why do carbon film fixed resistors have higher noise, and does it matter?
A3: Carbon film resistors have high current noise (~-10dB at 1kHz) because the amorphous carbon film has microscopic molecular gaps and irregularities-these gaps create small voltage fluctuations (noise) when current flows through the resistor.
Noise only matters for low-level signal paths (e.g., high-end audio, medical ECG/EKG, sensor biasing)-in these circuits, carbon film noise will corrupt weak signals and ruin performance. For basic circuits (LED current limiting, transistor biasing, switching), signal levels are high, and noise is completely negligible.
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