What Is a Carbon Film Resistor?
A carbon film resistor is a cheap, general-purpose resistor made by coating a ceramic body with a thin carbon film. For years it was the most common leaded resistor.
Its Structure
A carbon film is deposited on a ceramic rod and etched into a spiral to set the desired resistance. Connection leads are added at the ends.
Properties
| Property | Value |
|---|---|
| Tolerance | Usually ±5% |
| Noise | Relatively high |
| Temperature stability | Medium |
Advantages and Disadvantages
It's very cheap and adequate for general-purpose use; but for precision circuits it isn't as stable and low-noise as metal film.
Where Is It Used?
In general circuits where precision isn't critical, hobby projects and educational applications. Its value is read from color bands.
Power Ratings
Leaded carbon film resistors are most common at 1/4 W and 1/2 W; the larger the body, the more power it can carry. Calculating the dissipated power and choosing the right wattage (power selection) prevents overheating and value drift.
Common Mistakes
- Using it where precision matters: in measurement/reference circuits the tolerance and noise fall short.
- Exceeding the power rating: above the nominal wattage it overheats and its value drifts.
- Ignoring the temperature coefficient: the value can change with temperature.
Frequently Asked Questions
Carbon film or metal film?+
Are carbon film resistors still used?+
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