Different Types of Fixed Resistors and their Functions

Resistors are considered among the most vital components in an electronic circuit. Their function can go from providing power to preventing short circuits. Therefore, resistors are an integral part of every power supply and build with the electronics that you use on a routine basis. 

Fixed Resistors are the most commonly used resistors in electronic circuits as the name indicates, they have fixed resistance values that cannot be varied. In other words, this is ohmic resistance that cannot be adjusted. They are usually available in axial led and surface mount packages and other customized options majorly depending upon their applications. Axial led resistors used to be popular but nowadays the surface mount resistors are making fixed resistors more popular. 

Types of Fixed Resistors

There are different types of fixed resistors available in the market. Some of the main types are as follows:

Wire wound resistors

Carbon composition resistors

Carbon film resistors

Metal film resistors

Metal-oxidede film resistors

Metal glaze resistors

Foil resistors

Wire wound resistors

The wire-wound resistor is a sort of component that is constructed by winding a metal wire around a metal core. The metal wire performs as the resistive element to the electrical current. The resistance is imposed by the metal wire. The metal core performs as the conductive material but it does not let the electric current pass through it. The metal wires are generally either nichrome or manganin because of their high resistance to electric current.

Carbon Composition Resistors

The carbon composition resistor is also a passive component that restricts the electric current to a certain extent. These are constructed from cylindrical resistive elements that feature embedded metal end caps. The cylindrical resistive element is made from a mixture of ceramic and carbon powder. This carbon powder has good electrical conductance properties. These resistors were the most used types in the early 1960s. However, nowadays they rarely used because of their low stability and high cost.

Carbon Film Resistors

Carbon film resistors are popularly used in electric circuits. these resistors are constructed by placing the carbon film on a ceramic substrate. The carbon film has resistive properties due to which it is used as the main resistive element in these resistors. Whereas ceramic functions as the insulating material to the electric current. 

The resistive element has metallic end caps fitted at both of their ends. The leads are constructed from copper and attached to the two ends of the end caps. The carbon film resistors operate by creating less noise than the carbon composition resistors.

Metal Film Resistors

The metal film resistor is a Passive Components that uses a metal film to restrict the flow of electric current to a certain extent. They are similar in construction to the carbon film resistors. The main difference is the material that is used in the composition of the film. The film is constructed from metal for the electric flow adjustment. 

Metal film resistors have a low-temperature Co-efficient of Resistance. The rate at which the resistance of the material goes through some changes with rising temperature is called TCR.

Metal Oxide Film Resistors

The materials used in forming the resistive film are made from metal oxide such as tin oxide. They have a similar construction to the metal film resistors except for the material used for the film. These are less expensive compared to carbon composition resistors. They are known for operating at high temperatures. 

Metal Glaze Resistors

In this resistor, a mixture of metal particles and glass powder is used to restrict the flow of electric current to a certain extent. These Resistors have decreased TCR also known as the temperature Co-efficient of resistance. From TCR we can tell that when the temperature increases, the resistance of the material will also change. Metal glaze resistors commonly used in nuclear devices, IR image converters, communication devices, navigational radar, particle accelerators, voltage dividers, etc.

Foil Resistors

The most precise and stable components that used to restrict current flow are foil resistors. These resistors comparatively generate less noise than other types of Fixed Resistors. Another name used for foil resistors is high-precision resistors and they have reduced TCR. They used in audio components, oil rings, aviation, electronic sales, etc.

Conclusion

After briefly being introduced to the various resistor types you will have some idea about their composition and applications. It is always important to well informed regarding such electronic components before purchasing them as this will help you avoid any wrong purchases. Therefore, make sure that the fixed resistors you choose are suitable for the application you will use them.

Fixed resistor-Types of fixed resistors, definition and symbol

Fixed resistor

Fixed resistors are the most frequently used resistors in the electronic circuits. These resistors have the fixed resistance value. Hence, it is not possible to vary the resistance of the fixed resistor.

Resistance definition

The process of restricting the flow of electric current to certain level is called resistance. The device or component used to restrict the flow of electric current to certain level is called resistor.

The device, which only restricts the flow of electric current to certain level but does not vary or control the flow of electric current is called fixed resistor.

Fixed resistor definition

Fixed resistors are the resistors whose resistance does not change with the change in voltage or temperature. Fixed resistors are available in various shapes and sizes.

An ideal fixed resistor provides a constant resistance under all environments. However, the resistance of the practical resistors varies slightly with increase in temperature.

The most frequently used resistance values of the fixed resistors include 100KΩ, 10kΩ, 100Ω, 10Ω.

The cost of fixed resistors is high when compared to the cost of variable resistors, because each time to change the resistance we need to buy a new fixed resistor. In case of variable resistors, we use a single resistor for different resistance values. The resistance of the fixed resistor is measured by using the ammeter.

Symbol of fixed resistor

The IEC (International Electro-technical Commission) standard and American standard fixed resistor symbol is shown in the below figure.

A fixed resistor consists of two terminals. This two terminals are used to connect with the other components in the electronic circuit.

Types of fixed resistors

The different types of fixed resistors include:

Wire wound resistor

The wire wound resistor is a type of passive component, which is made by winding the metal wire around a metal core. The metal wire acts as the resistive element to the electric current. Hence, the metal wire restricts the electric current to certain level. The metal core acts as the non-conductive material. Hence, it does not allow electric current through it.

A manganin or nichrome is generally used as the metal wires because they provide high resistance to the electric current.

Carbon composition resistor

The carbon composition resistor is a type of passive component, which restricts the flow of electric current to certain level.

The carbon composition resistors are made from a cylindrical resistive element with embedded metal end caps. The cylindrical resistive element of the carbon composition resistor is made from the mixture of carbon powder and ceramic. The carbon powder acts as the good conductor of electric current.

The carbon composition resistors are the most frequently used resistors in the 1960’s and earlier. However, now a days these resistors are rarely used because of its high cost and low stability.

Carbon film resistor

Carbon film resistors are the most widely used resistors in the electronic circuits. The carbon film resistors are made by placing the carbon film on a ceramic substrate. The carbon film acts as the resistive element to the electric current and the ceramic substrate acts as the insulating material to the electric current.

The metallic end caps are fitted at both ends of the resistive element. The leads made of copper are joined at two ends of these end caps. The carbon film resistors produce less noise than carbon composition resistor.

Metal film resistor

The metal film resistor is a type of passive component in which metal film is used to restrict the flow of electric current to certain level. The construction of metal film resistor is almost similar to the carbon film resistor. The only difference is the material used for constructing the film. In carbon film resistors, the film is constructed by using carbon whereas in metal film resistors the film is constructed by using nickel chromium or tin and antimony.

Metal film resistors have low TCR (Temperature Co-efficient of Resistance). The rate at which the resistance of the material changes with increase in temperature is called TCR.

Metal oxide film resistor

The metal oxide film resistor is a type of passive component in which metal oxide film is used as the resistive element to restrict the flow of electric current to certain level.

The construction of metal oxide film resistor is almost similar to the metal film resistor. The only difference is the material used for constructing the film. In metal film resistor, the film is constructed by using the metals such as nickel chromium whereas in metal oxide film resistors, the film is constructed by using the metal oxide such as tin oxide.

The cost of metal oxide film resistor is low compared to the carbon composition resistor. These resistors operate at high temperatures.

Metal glaze resistor

The metal glaze resistor is a type of passive component in which glass powder and metal particles mixture is used to restrict the flow of electric current to certain level.

Metal glaze resistors have low TCR (Temperature Co-efficient of Resistance). The rate at which the resistance of the material changes with increase in temperature is called TCR.

Foil resistor

Foil resistors are the most accurate and stable components used to restrict the flow of electric current to certain level. Foil resistors produce low noise compared to the other types of resistors. These resistors are also called high precision resistors. Foil resistors have low TCR (Temperature Co-efficient of Resistance.

Basic Electronics - Fixed Resistors

Basic Electronics - Fixed Resistors

Fixed resistors are one type of linear resistors. A resistor is said to be a fixed resistor, if its value is fixed. The value of fixed resistor can’t be varied like a variable resistor as its value is determined at the time of manufacturing itself. The following figures represent the symbol of a fixed resistor.

The fixed resistors are classified into different types, depending upon their manufacturing processes and the materials used in their manufacturing. The classification is as follows.

Carbon composition

The Carbon composition resistors are a blend of carbon particles, graphite and ceramic dust mixed with a binder substance like clay. This mixture is treated with high pressure and temperature. After the whole thing is molded in a case, the leads are fixed.

Thermal mass of the carbon composition resistor is higher so as to withstand high energy pulses.

These resistors have low stability and high noise which is a disadvantage.

The following figure shows an image of carbon composition resistor.

Carbon composition resistors are used in Surge protection, Current limiting, and High voltage power supplies.

Wire wound

A Wire wound resistor is formed by wounding a wire made up of a resistive material around a core. The metallic core acts as a non-conductive material while the resistive wire conducts, but with some resistance. The image of a wire wound resistor is as shown below.

Usually a nichrome wire or a manganin wire is used to wind the core because they offer high resistance. Whereas plastic, ceramic or glass is used for core.

Wire wound resistors are very accurate.

They work excellently for low resistance values and high power ratings.

These are the oldest type of fixed resistors, but are being used even now.

Thick Film

The film resistors have a resistive layer on a ceramic base, whose thickness defines the type they belong to. The thickness of resistive layer on thick film resistors is much higher than thin film resistors. Thick film resistors are produced by firing a special paste, which is a mixture of glass and metal oxides, onto the substrate.

There are three main types in thick film resistors like Fusible resistors, Cermet film resistors, and Metal oxide film resistors.

Fusible Resistors

The Fusible resistors are similar to wire wound resistors. But these resistors along with providing resistance, act as a fuse. The image of a fusible resistor is as shown below.

In this resistor, the current flows through a spring loaded connection, which is placed closely to the body of the resistor. The blob that is attached to the spring wire of the resistor takes the heat generated by the resistor due to the current flow. If this heat is increased, the attachment to the blob gets melted up and opens the connection.

Hence we can say that, these resistors limit the current, but if the circuit power rating exceeds a specified value, these resistors act as a fuse to open or break the circuit. The value of these resistors is usually of less than 10 Ohms. These resistors are generally used in TV sets, amplifiers and other expensive electronic circuits.

Cermet Film Resistors

The Cermet film resistors are the film resistors made up of a special material called Cermet. Cermet is a composite alloy made by combining Ceramic and Metal. This combination provides the advantages in both of these materials like high temperature resistance and wear resistance of ceramic along with flexibility and electrical conductivity of a metal.

A metal film layer is wrapped around a resistive material and is fixed in a ceramic metal or cermet substrate. Leads are taken to make the connections easy while fixing on a PCB. They offer high stability as temperature cannot affect their performance.

Metal Oxide film resistors

A Metal oxide film resistor is formed by oxidizing a thick film of Tin chloride on a heated glass rod, which is a substrate. They have high temperature stability and can be used at high voltages. These resistors have low operating noise.

Metal oxide film resistors differ with metal film ones only regarding the type of film coated. Metal oxide is a metallic compound like tin with oxygen to form tin oxide, which is coated as a film on the resistor. The resistivity of this resistor depends upon the amount of antimony oxide added to the tin oxide.

Thin Film

Thin film resistors have a resistive layer of width 0.1 micrometer or smaller on the ceramic base. Thin film resistors have a metallic film that is vacuum deposited on an insulating substrate.

Thin film resistors are more accurate and have better temperature coefficient and is more stable. The thin film resistors are further divided into two types such as −

Carbon film resistors

Metal film resistors

Carbon film resistor

A Carbon film resistor is made by depositing a carbon film layer on a ceramic substrate. The carbon film acts as the resistive material to the current and the ceramic substance acts as an insulating substance. Metallic caps are fixed at both the ends and copper leads are drawn out.

The following figure shows the construction of a carbon film resistor.

The main advantages of these resistors are their high stability, wide operating range, low noise, and low cost. The carbon film resistors are the most preferred ones over carbon composition resistors due to their low noise.

Metal Film Resistors

The film coating makes the difference between metal oxide film resistors and metal film resistors. A thin film of metallic substance such as nickel chromium is used to coat the resistor in a metal film resistor whereas a film of metal oxide like tin oxide is used to coat the resistor in a metal oxide resistor.

Metal film resistors have low temperature coefficient of resistance, which means the resistance is less affected by the temperature.

Wattage

While using a resistor, if the flow of current increases, the resistor dissipates some heat. If this value crosses a certain critical value, the resistor may get damaged. The wattage rating of a resistor is printed on some higher value resistors in order to avoid such situation.

Wattage is the amount of electric power expressed in watts. Electric power is the rate of transfer of electrical energy.

Power P = VI = I2R

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