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Carbon film resistors are known for being cheap and available in a wide range of values. Standard tolerance is typically ±5%, though ±2% versions exist. The temperature coefficient of resistance (TCR) is generally higher than that of metal films, usually in the range of -200 to -500 ppm/°C. This means the resistance value drifts more as the component heats up or cools down. The noise characteristics are also inferior to metal film. Carbon film resistors exhibit higher thermal and current noise, making them a poor choice for sensitive analog circuits such as audio preamplifiers or precision instrumentation.
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Parameter
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Carbon Film Resistor
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Metal Film Resistor
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Tolerance
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±5% (standard), ±2% (available) | ±1% (standard), ±0.1% to ±0.01% (precision) |
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Temperature Coefficient (TCR)
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-200 to -500 ppm/°C | ±50 to ±100 ppm/°C |
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Noise (Current Noise Index)
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Moderate to high (-12 to -6 dB) | Very low (-40 to -30 dB) |
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Long-Term Stability
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1-3% drift over 1,000 hours | 0.1-0.5% drift over 1,000 hours |
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Max Operating Temp
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155°C (typical) | 155°C to 175°C (typical) |
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Pulse Load Handling
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Good | Moderate (film can crack under extreme pulses) |
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High-Frequency Performance
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Poor (capacitive effects) | Better (lower parasitic capacitance) |
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Price (1/4W, 1kΩ, volume)
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$0.02 – $0.05 | $0.05 – $0.15 |
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Typical Use Case
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Consumer electronics, general purpose | Precision analog, audio, medical, test equipment |
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Application Category
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Recommended Type
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Typical Tolerance Needed
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Why This Type
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| Pull-up / pull-down resistors | Carbon Film | ±5% | Value not critical, cost matters |
| LED current limiting | Carbon Film | ±5% | LED Vf variation dominates anyway |
| General voltage dividers | Carbon Film | ±5% | Ratio accuracy usually not critical |
| Op-amp feedback networks | Metal Film | ±1% or better | Gain accuracy depends on ratio |
| Audio signal path | Metal Film | ±1% | Low noise required |
| Current sense (precision) | Metal Film | ±1% or better | Drift affects current limit accuracy |
| Active filters (Sallen-Key, etc.) | Metal Film | ±1% | Cutoff frequency depends on RC product |
| Wheatstone bridge circuits | Metal Film | ±1% or matched | Balance depends on ratio matching |
| Reference voltage dividers | Metal Film | ±0.1% or better | Output voltage depends on divider ratio |
| Snubber / bleeder / discharge | Carbon Film | ±5% | Pulse handling and cost matter |
| RF circuits (above 10 MHz) | Neither (use thin-film chip) | ±1% | Parasitics too high for axial types |
| Medical instrumentation | Metal Film | ±1% or better | Stability and low noise are regulatory requirements |
| Automotive sensors | Metal Film | ±1% | Temperature stability over -40°C to +125°C |
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Symptom
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Most Likely Cause
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Solution
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| Resistor body is discolored or charred | Power rating exceeded; resistor running too hot | Recalculate power dissipation (P = I²R or V²/R); use higher wattage or multiple resistors in parallel |
| Resistance value has drifted high over time | Carbon film oxidation; thermal stress from overload | Switch to metal film for better stability; add derating margin (use at ≤50% rated power) |
| Circuit noise floor is unexpectedly high | Carbon film resistors in sensitive signal path | Replace signal-path resistors with metal film or thin-film chip resistors |
| Voltage divider output drifts with temperature | High TCR carbon film resistors in temperature-varying environment | Replace with metal film (±50 ppm/°C) or matched resistor network |
| Resistor fails open after power surge | Pulse overload cracked metal film; insufficient pulse rating | Use carbon film for better pulse tolerance, or select pulse-rated metal film series |
| Gain error in op-amp circuit varies with temperature | Feedback resistor TCR too high; mismatch between input and feedback resistors | Use metal film with matched TCRs; consider integrated thin-film resistor networks |