Carbon Film Resistor – Working & Its Applications

• When a resistor uses carbon film to limit the flow of electric current until a particular level it is known as a Carbon Film Resistor.

• The symbol of this resistor is similar to that of the normal resistor.
• Here, the carbon works as the resistive material.

Construction of a Carbon Film Resistor

• A carbon film is deposited on a substrate of ceramic. This carbon film restricts the flow of the current of the resistor.

• The Ceramic rod acts as a substrate and provides insulation to the resistor from electricity and high temperature.
• The helical shape of the resistor helps receive precise resistance from the resistor. Thus, the resistance value can be adjusted by reducing helical path length.
• An epoxy coat is provided to protect the resistor The end caps are connected to the metal lead wire which is mostly made up of copper metal.
• These resistors have a higher(than normal resistors) negative temperature coefficient (NTC)  the resistance produced increases with a decrease in temperature. This is because it uses a pure carbon material.

• The resistance value can be determined by the thickness of the carbon film material.

specifications of Carbon Film Resistor

• The power rating range is from 0.125 W to 5 W(at 70°C).
• Resistance range from 1 ohm to 10 mega ohms.
• The operating temperature ranges from −55 °C to 155 °C.
• The maximum working voltage ranges from 200 to 600 volts.
• Tolerance accessibility is ±2%, ±5%, ±10%, ±20%.
• Max noise is 20 µV/V.
• The temperature coefficient ranges from ±200 to ±1500 ppm/°C.
• The voltage coefficient is 0.0005 %/V.
• Max resistor temperature is 150 °C.

If we compare metal film resistor with carbon film resistor

Metal Film Resistor

• Metal film resistor uses a thin metal film to restrict the flow of current.
• As compared to carbon film resistors, these resistors have high accuracy and high stability.
• These are small in size and less expensive.

Carbon Film Resistor

• A carbon film resistor uses a thin carbon film to restrict the current flow.
• These resistors have less accuracy as compared to metal film resistors and low stability.
• These resistors are not small in size.
• These resistors are expensive as compared to metal film-type resistors.