What is a Film Resistor : Working & Its Applications

A resistor is an essential component in electrical and electronic circuits. There are different types of resistors available in the market which can be made with different materials like wire wound resistors, carbon composition resistors, film resistors, carbon film, metal film, fusible, surface mount, thermistors, etc. These resistors have their own benefits and drawbacks. So this article discusses one of the types of resistor namely film resistor – working, types and its applications.

What is a Film Resistor?

The definition of a film resistor is; a fixed resistor that has the resistance element like a thin conductive material layer in an insulated form is known as a film resistor. The conductive material does not include insulating material or binders. The function of a film resistor is to restrict some amount of current within a circuit. These resistors are applicable where a more accurate value or high tolerance is required. So these are used in filter circuits, less noise analog signal circuits & bridge circuits.

Construction & Working

The construction of a film resistor can be done by depositing very pure materials on the substrate or an insulating ceramic such as nickel or oxide film like tin-oxide. These resistors are usually designed with small ceramic rods which are coated with metal like a nickel alloy or a metal oxide like tin oxide. Here, the resistance value can be controlled by the width of the coating layer. So if the layer is thicker then the resistance value will be low. The resistance of the film resistor ranges from 1 ohm to 10 megaohms.

Types of Film Resistors

Film resistors are available in different types like metal film, carbon film, metal oxide film, thick film, and thin-film resistors where each type is discussed below.

Carbon Film Resistor

Fixed types of resistor that uses a carbon film to limit the flow of current at a fixed level are known as carbon film resistor. These resistors are extensively used in different electronic circuits. The construction of this resistor can be done by arranging the carbon film over a ceramic substrate. So carbon film material works as the resistive material to the flow of current. Thus, this material blocks some amount of current.

The ceramic substrate of this resistor works as the insulating material to the electricity or heat. So, the ceramic substrate restricts heat throughout them. These types of resistors can resist temperatures without any harm. As compared to carbon composition resistors, these resistors are frequently used because the carbon film resistors generate low noise.

Metal Film Resistor

The resistor that uses a thin metal layer on a non-conducting body as the resistive element is known as a metal film resistor. These resistors are made with small ceramic coated roads with metal like nickel alloy. These resistors are very expensive as compared to carbon film-type resistors.

The construction of these resistors can be done by placing a homogeneous pure carbon film over a ceramic, glass otherwise other insulating core material. The resistance value of this resistor can be simply controlled through the width of the coating layer. These resistors are used where a more accurate or high tolerance value is required.

Metal Oxide Film Resistor

A fixed resistor that uses a metal oxide film material as the resistive element to restrict the current flow in a circuit to a fixed level is known as a metal oxide film resistor. The construction of this resistor is almost the same as the metal film type resistors except for the material used. In this type of resistor, the film can be designed through metal oxide material like tin oxide.

So this resistor can be constructed by the ceramic core coating through metal oxide like tin oxide. The resistivity can be increased by adding antimony oxide to the tin oxide material.

In this type of resistor, the required resistance can be attained by slashing the metal oxide film within a helical form. Once the required resistance value is obtained, then metal oxide film slashing can be stopped. Here, the laser is used to cut metal oxide film in a helical manner.

Thick Film Resistor

These resistors are designed by applying a mixture of glass, paste, or resistive film & conductive materials to a substrate. The technology of Thick-film permits high resistance values which can be marked on a flat or cylindrical substrate either enclosed completely otherwise in a variety of patterns. They can also be printed in a serpentine design to reduce inductance, so these are applicable where steady frequencies are used.

Thin Film Resistor

The resistor that uses a thin resistive layer on a ceramic base resistor is known as a thin-film resistor. The thickness of the resistive layer of this resistor is approximately 0.1 microns. Generally, these resistors are more stable and accurate which allows them to be utilized within high precision technologies.

Film Resistor Color Code

Generally, resistors are color-coded with different colors to recognize their resistance value, % of tolerance & wattage rating. Usually, these three values are printed on the resistor body. When the resistor has letters or numbers on the body then called a large power resistor.

The resistor color code can be calculated through different color bands. These color bands will denote the values of resistance, tolerance & sometimes failure rate, or reliability. The color bands on the resistor vary from a minimum of two bands to six bands.

Please refer to this link to know more about Resistor Color Code Calculation.

Advantages and Disadvantages

The advantages of Film Resistor include the following.

• Caron film resistor advantages are; small size, stability, reliability, and low tolerance.
• Metal film resistor advantages are; low noise, good temperature stability, tolerance is better and accessibility for an extensive range of power ratings.
• The advantages of metal oxide film resistors are; less cost, small size, high reliability & stability, and less noise & operation at high temperatures.
• Thick film resistors provide high resistance values, are more resistant to dampness, are small in size, economical, etc.
• Thin-film resistors achieve low tolerances, less noise, lower capacitance & parasitic inductance, etc.

The disadvantages of Film Resistor include the following.

• Caron film resistors involve in high temperature & high voltage based applications like power supplies, X-rays, RADAR, etc
• Metal film resistors are used where high accuracy and tolerance values are required within a circuit. These are used in filter circuits, bridge circuits & less noise analog signal circuits.
• Metal oxide film resistors are used where the requirements of power dissipation are > 1 W & maximum stability is necessary.
• Thick film resistors are literally applicable in each type of electrical device which uses an AC plug or battery.
• Thin Film resistors are normally used where; high accuracy, low noise, or high stability is required like monitoring equipment, test & measurement equipment, audio applications, medical equipment, instrumentation, etc.

Thus, this is all about an overview of a film resistor – its types, and its working with applications. Generally, film resistor characteristics are; stability, TCR, and tolerance. These resistors feature high linearity & fewer noise properties due to less voltage coefficient. Here is a question for you, what is a power resistor?