What is Fixed Resistor : Working & Its Applications

Resistors are one of the most crucial components in any electronic circuit. From providing power to preventing short circuits, resistors are an integral part of every power supply and build with the electronics you use on a daily basis. The Fixed Resistor also known as “linear” or “ohmic” resistors invented by George Westinghouse and William Stanley, Jr. is a resistor that has a solid, fixed value for all their characteristics, like their resistance and power ranking, at all times.

This article will discuss what these fixed resistors do as well as their function in circuits today to help you understand how they work, their types, and how to properly apply them along with their advantages and limitations.

What is Fixed Resistor?/Definition

A fixed resistor is an electrical resistor with a fixed value. Resistors receive a voltage and restrict the amount of current that flows through it, to create a different voltage and reduce power by turning it into heat.

Fixed resistors are the most common type of resistor in electronic circuits. These are mainly for restricting the flow of current, dividing voltages & signal level adjustment. They are also used as current-sensing components for protection circuits and for making corrections for other circuit parameters.
To learn more about the basic properties and applications of standard resistors, check out our article ‘What is a resistor.’

How Does a Fixed Resistor Work?

A fixed resistor is a two-terminal passive component that is used to implement electrical resistance like a circuit element. The flow of current throughout this resistor is directly proportional to the voltage supply across the two terminals of this resistor. So, this relationship can be simply signified by using Ohm’s law:

V = I × R

Where ‘V’ is the voltage across the resistor, ‘I’ is the current through the resistor and ‘R’ is the resistance value. For example, if a 100-ohm resistor is connected across a 10-volt potential difference, then a current of 0.1 amperes flows through that resistor.

Fixed Resistor Construction

A fixed resistor has two main parts: the resistive element, which is usually wire wound into a coil, and the outer casing, which may be made of plastic, ceramic, or metal depending on the application. The resistive element is usually coil-shaped in order to increase its surface area without taking up too much space.

The resistance of the fixed resistor depends on its length, diameter, and material properties. The length and diameter can be adjusted during production or after manufacturing by adding more wire or removing it. The material properties can’t be changed once the resistor is manufactured, although they can be measured and recorded to improve efficiency when designing new products.

Fixed Resistor Symbol

Resistors with a fixed value are often depicted using one of the following symbols. The most commonly used symbol is the international IEC resistor (Left), but the American resistor symbol (right) is also still in use today.

Fixed Resistor Values

Fixed resistors can have values ranging from 0 to 100 Gigaohms.

Fixed resistors come in many varieties and have different values. The value of a resistor is indicated by its color bands, which are arranged in order from the most to the least significant values. The first two bands indicate the first and second digits, while the third band indicates the number of zeros to add after those two digits. For example, a resistor with red, green, yellow bands would be 27000 ohms.

Fixed Resistor Colour Code

The fixed resistor color code is used to indicate the value or magnitude of resistance of a resistor. The fixed resistor is a resistor whose value cannot be adjusted after installation. It is possible to determine the value of resistance by identifying the band colors and then looking up the corresponding values in a table.

Fixed resistors have four bands that are marked with different colors, and each band represents an important piece of information: the first two bands represent the resistance value, while the third band denotes its tolerance. The fourth band is sometimes included on metal-film resistors—however, they can also just be blank or have a gold stripe. So let’s take a closer look at each band and what it means:

• The first and second bands both represent numbers in ohms. For example, if the first band is brown and the second band is black, you know that the resistance value is 100Ω.
• The third band indicates how much variance there is from this nominal resistance value; for example, if the third band is red, then this means that there can be a percent tolerance of 2%.
• The fourth band is either gold or silver; these metals indicate 5% tolerance.
• Sometimes a fifth band can indicate failure rate.

Types of Fixed Resistor

There are several different types of fixed resistors. The most common are:

1). Carbon-composition Resistor.

2). Wirewound Resistor.

3). Thin-film resistor

• Carbon-film Resistor
• Metal Film Resistor

4). Thick film resistor

• Metal Oxide Film Resistor.
• Cermet oxide resistor.
• Fusible resistor.

5). Sand-cast Resistor.

6). Metal glaze resistor.

7). Foil resistor.

8). Precision Wire resistor.

9). Power Wire resistor.

10). Metal Glaze resistor.

Carbon-composition Resistor

They consist of a mixture of graphite and clay that’s molded into a cylindrical shape with two lead wires attached to each end. They come in a variety of resistance values, tolerances, and power ratings.

Carbon-composition resistors work well when they’re used at low frequencies and low power levels, but they aren’t ideal for high frequencies or high power levels because they tend to absorb moisture from the air. They also tend to be noisier than other types of resistors (i.e., produce more voltage noise).

Wirewound Resistor

A wire-wound resistor consists of a rectangular length of a ceramic-coated glass rod with a wound metal wire running through its center. The wire is connected at both ends to copper terminals that extend from the top and bottom of the ceramic case.

The two primary types of wire wound fixed resistors are precision wire wound resistors and power wire wound resistors.

Thin Film Resistor

The thin-film resistor is generally made with a resistive material and also a high grid ceramic rod. These resistors have a thin resistive layer that is located on top of a ceramic base.

The main difference between thin and thick film resistors is the width of the resistive layer. These resistors have around 0.1 microns thickness. These resistors are available in two types carbon film and metal film.

Carbon-film Resistor

A carbon-film resistor is one type of fixed resistor that uses a carbon film as its resistive element. This is made by coating the surface of a ceramic core with carbon powder and then baking it at a high temperature. The resistive value is controlled by varying the length and thickness of the film, and also by laser trimming it during post-production.

Carbon-film resistors are inexpensive and widely available. They are typically used for applications that require a resistance between 100 ohms and 1 megaohm (1,000,000 ohms).

Metal Film Resistor

Metal film resistors are made using a process similar to that used for carbon film resistors, but instead of applying the resistor element as a carbon film, it is applied as a metal film. Metal film resistors are used in applications where stability is important, such as in audio equipment.

They also have a low level of noise and temperature coefficients. Because they’re made from metals instead of carbon, they tend to be more durable than carbon film resistors. Metal film resistors are the most common type of resistor on the market.

Thick Film Resistor

The design of Thick film resistors is similar to thin-film except for the resistive material layer like thick film. These resistors are available in three types metal oxide, fusible and cermet film resistor.

Metal Oxide Film Resistor

This is a type of fixed resistor that uses a resistive element like thin metal oxide film. It is similar in construction to the carbon film resistor, but the metal oxide material provides higher temperature stability and lowers noise characteristics. They’re more stable than carbon and metal film resistors and provide excellent temperature performance.

Metal oxide resistors are often used in low-power applications, such as audio electronics and small power supplies, where their performance qualities make them preferable to cheaper carbon film resistors.

Cermet Oxide Resistor

These resistors are also known as network resistors. In these types of resistors, the inside region mainly includes ceramic insulation materials, and a metal alloy or carbon film layer is wrapped around the cermet resistor. These resistors are designed in a rectangular or square shape & the terminals are used for connecting in PCBs (printed circuit boards) easily. These resistors offer a stable operation within maximum temperature as their resistance values do not vary when the temperature changes.

Fusible Resistor

This is a special kind of resistor that is used to protect any circuit. The material used to make this resistor has fusing characteristics without surplus heat generation or flames once the current load moves suddenly more than necessary. These resistors are used in highly sensitive circuits where the surge handling, as well as overload requirement, is not very severe. Please refer to this link to know more about the fusible resistor.

Precision Wire Wound Resistor

Precision wire wound resistors feature a low resistance value ranging from less than 1 ohm to approximately 100 Kilo ohms with a low tolerance rating, typically no greater than 1%. The power rating for this type of fixed resistor is relatively low with typical ratings ranging from less than 1 watt to approximately 20 watts.

Power Wire Wound Resistor

Power wire wound resistors also feature limited resistance values; however, their resistance values range from less than 1 ohm to several megaohms. The power rating for this type of fixed resistor is much higher than those offered by precision wire wound resistors with typical ratings ranging from 10 watts to hundreds of watts or more.

Metal Glaze Resistor

This is one kind of passive component where the mixture of metal particles & glass powder is mainly used to limit the electric current flow to a fixed level. These resistors have less temperature coefficient of resistance or TCR. Here TCR is when the temperature increases then the resistance of the material changes.

Metal glaze resistors are used in IR image converters, nuclear devices, navigational radars, communication devices, voltage dividers, particle accelerators, etc.

Foil Resistor

The most stable and precise components are Foil resistors which are used to limit the current flow to a certain range. As compared to other types of resistors, these resistors generate less low noise. An alternate name of this resistor is a high precision resistor and these resistors have less TCR. The applications of foil resistors mainly include aviation, oil rings, audio components, electronic scales, etc.

Differences between Fixed Resistor and Variable Resistor

The main difference between a fixed resistor and a variable resistor is discussed below.

Fixed  Resistor	Variable Resistor
The fixed resistor has a fixed value of resistance.	The variable resistor has a varying value of resistance.
Fixed resistors have their values printed on them so they cannot be changed	Variable resistors can have their values changed as they are not printed on them.
These resistors are available in different types like thin film, thick film, surface mount, wire wound, metal film chip & metal oxide resistors.	These resistors are available in three types trimmer, potentiometer, and rheostat.
This resistor includes two terminals that are used to connect different components in a circuit.	Variable resistor includes three terminals where two terminals are fixed and another terminal is movable which is called the wiper.
The materials used in this resistor are a manganin wire or nichrome wire for winding the core because they provide high resistance and glass, ceramic, or plastic are used for the core.	A variable resistor includes a resistance track that is made with carbon, cermet, or a wire coil.
These resistors restrict the current flow in a circuit at a certain level.	These resistors are used to regulate the voltage or current values in a circuit.
A fixed resistor is used in amplifiers, TV sets & other costly electronic circuits.	A variable resistor is used in a dimmer switch for light & the knob for volume control on a radio.
The resistance values of these resistors mainly include 10Ω, 100Ω,10kΩ & 100KΩ.	The resistance values of the variable resistor range from ‘0’ to a certain highest value.

Advantages & Disadvantages

The advantages of a fixed resistor are discussed below.

• Lower Cost—high power and high-performance carbon film resistors are inexpensive.
• Low Noise—carbon film resistors result in low noise levels compared with other types of resistors.
• Small Size—carbon film resistors, particularly thick film, and thin-film types have small sizes compared with other types of resistors.
• High Stability—carbon film resistors are more stable than metal oxide resistors because they are not affected by changes in temperature and humidity levels.

The disadvantages of a fixed resistor are discussed below.

• Low Power Rating – carbon film resistors have low power ratings. The maximum power rating is usually 1/8 watt or less.
• Decreased Accuracy—carbon film resistors are not as accurate as metal oxide resistors or wire wound resistors.
• Fixed Resistance Value – Resistance values can’t be adjusted once the resistors have been manufactured.
• They are not waterproof and cannot be used underwater.
• They can only withstand up to 1 volt per second.
• They are prone to noise and interference, especially if there is a lot of electromagnetic radiation around, due to their low resistance.

Applications/Uses

The applications of fixed resistors include the following.

• They are used in power supplies to reduce the incoming voltage, they can also be used in circuits to limit the flow of current, and they are used in heaters that need to dissipate heat energy.
• Fixed resistors are often used for biasing transistors and diodes, which means that they are used to set the working point (also known as Q-point) of active devices such as diodes and transistors.
• The fixed resistor may be placed at various points throughout the circuit, depending on its desired effect on the overall operation of the circuit.
• They are commonly used as pull-up resistors in digital circuits because they help prevent floating inputs from changing state due to noise or other interference.

What is the Main Purpose of a Fixed Resistor?

The main purpose of a fixed resistor is to control or limit the flow of electrical current in an electronic circuit. They are usually used with one or more other components such as capacitors, inductors, and transistors to form electronic circuits.

What are the Features of a Fixed Resistor?

Features of fixed resistors include:

• High stability and reliability.
• A wide range of resistance values, from very small to a gigaohm.
• Can be used in various environments and conditions, such as temperature, humidity, pressure, vibration, and radiation.
• Low noise generation.
• Low power consumption

Why are Fixed Resistors Ohmic?

Fixed resistors are ohmic because they have a fixed resistance or a resistance that’s not dependent on the amount of current flowing through the component.

This means that the same amount of voltage (V) will always turn into the same amount of current (I) when passing through a fixed resistor. The formula for this relationship is V = I x R, where R represents the fixed resistance.

Is Potentiometer a Fixed Resistor?

A fixed resistor is a type of resistor that has a fixed value. A potentiometer is also a type of resistor, but it’s not a fixed resistor. Instead, it has a variable value: the value changes according to whether you’re at the top or bottom of its range.

Both types of resistors help regulate the flow of electricity in a circuit, which can help protect the circuit from damage.

Thus, this is an overview of a fixed resistor which includes its types, differences, advantages, disadvantages, and applications. The two main characteristics of the fixed resistor are; nominal resistance value & maximum dissipation. The nominal resistance value is color-coded otherwise printed on the resistor body. Usually, the maximum dissipation is not marked on the resistor body, but the resistor’s specification will have its maximum dissipation by using these values like 0.125 W, 0.25 W, 0.5 W, etc. Here is a question for you, what is the tolerance value of a fixed resistor?