What Is a Carbon Film Resistor?
Carbon film resistors BTS50085-1TMA are made by evaporating and decomposing hydrocarbons at high temperature in a vacuum to form a carbon crystal conductive film. They have the characteristics of good resistance stability, wide resistance range, good high-frequency characteristics, low noise, and low price.
Description
Carbon film resistors BTS50085-1TMA are a type of film resistors. They are made by using high-temperature vacuum coating technology to tightly attach carbon to the surface of a porcelain rod to form a carbon film, then adding appropriate joints and cutting, and coating the surface with epoxy resin for sealing and protection. The surface is often coated with green protective paint.
Working Principle
The working principle of a carbon film resistor BTS50085-1TMA is based on the resistive properties of carbon. A thin layer of carbon is deposited on an insulating ceramic substrate through a process called pyrolysis, where a hydrocarbon gas is decomposed at high temperatures to form the carbon film. This film acts as the resistive element. The resistance value is precisely controlled by cutting a helical groove along the length of the carbon film. This groove increases the length of the path that the current must travel, thereby increasing resistance.
When an electric current passes through the resistor, the carbon film opposes the flow of electrons, converting some of the electrical energy into heat. The resistance of carbon film is uniform and stable, providing consistent performance. The amount of resistance is determined by the thickness of the carbon film, the width and depth of the helical groove, and the overall length of the resistive path.
Structure
Carbon film resistors are manufactured by using specialized equipment to decompose gaseous hydrocarbons in a high-temperature and vacuum environment. The decomposed carbon is evenly deposited on the circumferential surface of a ceramic cylinder or tube, forming a layer of crystalline carbon film.
To achieve the desired resistance value, the thickness of the carbon film is adjusted, and the spiral groove pitch is selected to determine the appropriate cross-sectional area and length of the carbon film. Following this, copper end caps are attached, leads are soldered, and the surface is coated with paint for packaging.
The width of the carbon film is inversely proportional to the resistance value, while the effective length of the carbon film is proportional to it. Additionally, the thinner the carbon film, the higher the resistance value. Carbon film resistors typically have low precision, with a maximum tolerance of ±5%. These resistors exhibit a negative temperature coefficient, meaning their resistance decreases as the temperature increases.
Features
Offers high precision with 2% or 5% accuracy
Broad resistance ranges typically from 2.1Ω to 10MΩ.
Capable of withstanding high voltages
Minimal resistance change due to voltage variations
Features a negative temperature coefficient.
Available in tape and bulk packaging options.
Low inherent noise electromotive force below 10μV/V.
Available in various power ratings including 1/8W, 1/4W, 1/2W, 1W, 2W, 5W, and 10W
Carbon Film Resistor vs. Metal Film Resistors
| Carbon Film Resistor | Metal Film Resistor | |
| Material Composition | Organic compound carbon film on ceramic rod | Nickel-chromium or similar alloy on ceramic rod |
| Manufacturing Process | High-temperature vacuum deposition, sealed with epoxy | Vacuum deposition, cut for precise resistance values |
| Precision | Low precision (±5%) | High precision (±1%) |
| Tolerance | Wider tolerance range | Narrower tolerance range |
| Appearance | Typically four color bands, usually tan or other colors | Typically five color bands, usually blue |
| Temperature Coefficient | Higher temperature coefficient | Lower temperature coefficient |
| Application | Used widely in consumer electronics, cost-effective | Used in precision applications, including fusing |
| Resistance Change | Resistance value changes significantly with temperature | Resistance value changes minimally with temperature |
| Color of Exposed Film | Black | Bright white |
| Stability | High reliability in general use | Higher stability and reliability in precision applications |