Tutorial 2
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We have familiarized ourselves with the basics of resistors and its application. In this article, we will learn about different types of Resistors and basic guidelines for choosing resistors based on different applications.
Before going into the detail about different types of resistors, let us revisit and understand again what is Electric Resistance.
Definition of ResistanceThe property of materials that opposes the flow of electric current through it is called resistance, in simple words resistance is an inherent property of materials that opposes the flow of current. We have covered about how resistors works in our previous tutorial.
Different Types of ResistorsWe know resistors are extensively used in different electronic circuits. Different types of resistors possess different characteristics and properties. Three major characteristics of resistance are ohms, power rating, and tolerance. The resistance of a resistor is measured in Ohms and its power rating is measured in Watt and the deviation from the manufactured value is known as tolerance.
Here, we will see in detail about different types of resistors. Based on working principle, material composition, and application use, we can divide resistors into two major types.
There are different types of resistors, Linear Resistors are such types of resistors whose resistance does not vary no matter how much voltage or current is applied. More formally we can define linear resistor as a type of resistor where the relationship between voltage and current obeys Ohms Law.
In simple words, in linear resistors, if we increase the voltage, the current increases in the same proportion, however, the resistor resistance value remains the same.
Furthermore, these are different types of resistors however, in broad case there are two major types of linear Resistors :
Fixed resistors are the most widely used resistors among different types of resistors in electronic devices. Fixed resistors are those whose resistance value does not change with the change in voltage or current. In simple words, its resistance remains constant and we cannot change it.
However, we find some deviation in the resistance of fixed resister with the temperature change. The symbol of a fixed resistor is shown below.
These fixed resistors are also further classified into different types based on the manufacturing process and the material used.
Carbon composition resistors are one type among the different types of resistors that fall under the category of fixed resistor. They are manufactured using resistive elements made by mixing carbon powder with some binder and compressed into the shape of a cylinder. Small metal leads are attached to the end and the entire body is coated with some protective materials.
Such resistors are available in the range of few ohms to mega ohms. They are still extensively used in electronic devices; however, their tolerance range is often between ±5% to ±20%. Among the different types of resistors, carbon composition resistors tend to generate more electrical noise, making them less preferred for high-precision applications.
Wire Wound ResistorsAmong different types of resistors, Wire wound resistors are a type of resistors made by winding a wire, typically made from an alloy of high-resistance materials around an insulating core. Such resistors have high accuracy and stability and offer excellent precision and tight tolerance levels.
These resistors generate very little electrical noise and are excellent for low-signal circuits. However, due to coil wire structure, wire wound resistors are not preferred in high-frequency applications as they may exhibit inductive behavior.
These resistors are available in the range of 2 watts up to 100 watts or more and can operate safely up to C or more.
Major Application of Wire Wound ResistorSince wire wound resistors can withstand large currents they are often used as dumb loads to dissipate large amounts of power.
Wire wound resistors are commonly used in precision measurement devices and high-accuracy analog sensors due to their stability over a long time.
These types of resistors can withstand a higher range of temperatures making them useful in temperature-sensitive applications.
Thin Film ResistorThin film resistors are more precision resistors and are manufactured by depositing a very thin resistive material layer overlaid on insulating materials usually a ceramic substrate. This layer thickness is usually in the range of a few nanometers up to micrometers making it suitable for highly accurate resistance value.
Since a thin coating of film is deposited on the insulating substrate, they are unable to handle large amounts of power.
Major Application of Film ResistorsThin film resistors are extensively used in medical devices and high-precision measurement equipment due to their high accuracy and stability.
Unlike wire wound resistors these resistors do not exhibit inductive behavior and due to low noise and stable performance they are preferred in high-frequency applications. They are often used in Radio Frequency circuits and communication devices.
Based on the composition nature these thin film resistors are further divided into two types
Among different types of resistors, the carbon film resistors are manufactured by depositing a thin layer of carbon on an insulated substrate. This kind of resistors is widely used in electronic circuits as they have tighter tolerance, and are more stable as compared to carbon resistors.
Metal Film ResistorsThe only difference between the carbon film and metal film resistor is the film coating. In a metal film resistor instead of carbon film a thin metallic substrate is coated on the insulating material to form a metal film resistor.
Metal film resistors are tiny, cheap, and reliable in operation. Compared to carbon film resistors metal film resistors offer several advantages: tighter tolerances, less sensitivity to temperature change, and lower noise.
Thick Metal Film ResistorsThick metal Film resistors are another variation of metal film resistors designed with a thicker layer of resistive metal material. Unlike thin film resistors, the deposition layer in thick metal film resistors is significantly thicker. This thicker deposition layer provides several advantages viz durability, high power handling, and stable performance.
Thick Film resistors are further divided into the following types:
Metal Oxide Resistors are manufactured by depositing a thick film of the Tin Chloride layer on a ceramic substrate. These resistors are available in a wide range and are known for their high-temperature stability, reliability, and high power compared to carbon-based resistors.
Cermet Oxide Resistors (Network Resistors)The word Cer-Met comes from two words Cermic and Resistor. This resistors are made from the composition of metal and ceramic. This composition of metal and ceramic provides the advantage: of high-temperature resistance and gradual wear of resistance. In such resistors multiple resistors are integrated into a single package, making it more compact. This saves space and makes it easier for fabrication in printed circuit boards.
Fusible ResistorsFusible resistors are almost similar to wire wound resistors, however, they come with a built-in fuse, hence the name fusible resistors. They are designed to operate similarly to the conventional resistor however, when the current flows above the power rating then the resistor is fused, i.e. it breaks the flow of current. This property makes them usable in overload protection.
They are widely used in power supplies, consumer electronics, and other expensive electronic circuits to protect against overcurrent or short-circuit situations. Such resistors generally have low ohmic values of less than 10 ohms.
Variable ResistorsAs the name indicates, variable resistors are among different types of resistors whose resistance value can be adjusted over a defined range. Most variable resistors have a movable dial, knob, or screw to manually adjust the required range. They consist of a fixed resistive element and a sliding contact (or wiper) that moves across the resistive material.
This design typically results in three terminals: one connected to the sliding arm and the other two to the fixed resistor. When all three terminals are used, the device functions as a variable resistor. Among the different types of resistors, these resistors are commonly used where it is necessary to adjust the resistance dynamically to control parameters like voltage current or signal.
This adjustability makes variable resistors useful in various applications, such as volume controls, light dimmer circuits, and sensor calibrations.
Working Principle of Variable ResistorsAlthough there are various types of variable resistors, their working mechanism remains fundamentally the same. When closely examined, variable resistors have a fixed resistance between terminals 1 and 3, known as the resistor track. The third terminal (terminal 2) is connected to a knob that has a wiper attached to it. This wiper moves freely across the resistive track as the knob is adjusted.
By changing the position of the knob, the wiper shifts along the resistive element, effectively dividing the track into two parts. This movement alters the resistance between terminal 2 and the other two terminals (1 and 3). As the wiper moves closer to one end of the track, the resistance between the wiper and that terminal decreases, while the resistance to the other terminal increases. In this way, adjusting the knob allows for different resistance values to be achieved within the circuit, providing precise control over the flow of current or voltage.
This simple yet effective mechanism makes variable resistors ideal for applications such as volume control, LCD brightness control, and sensor calibration where real-time adjustments are necessary.
Variable Resistors are further divided into the following major types:
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Potentiometers are three-terminal variable resistors commonly used for adjusting voltage levels within a circuit. They work by varying the resistance between two points along a resistive element, thereby allowing the creation of an adjustable voltage output.
Fixed Resistance: The resistance between the two terminals (Terminals 1 and 3) remains constant and acts like a fixed resistor.
Variable Resistance: The third terminal(Terminal 2), often attached with knob moves along the fixed resistive track (formed by terminals 1 and 2). By rotating this knob we can adjust resistance and output voltage.
This way, Potentiometers can be used as a voltage divider and these resistors are called variable composition resistors. They are available for up to 10 Mega Ohms. However, due to mechanical movement, the wiper can wear out, leading to degradation in performance.
Such manually adjustable Potentiometers are further divided into two broad types:
A rheostat is a type of variable resistor, which can have two or three terminals similar to potentiometers but are specially designed to control current. Unlike potentiometers which are used for voltage control, rheostats are extensively used to control the flow of current.
They are used for applications like motor speed control, heater regulation, and light dimmer circuits. Rheostats are also known as tapped resistors or variable wire wound resistors. Rheostats work similarly to the potentiometer but alter the effective resistance with the help of a wiper.
When the wiper moves closer to the start of the track this decreases the resistance allowing more current to flow. Similarly, moving the wiper further along the track increases the resistance hence reducing the flow of current.
So, what is the main difference between a Potentiometer and a Rheostat then?Although there are different types of resistors, the major types of variable resistors are potentiometer and rheostats. The potentiometer and rheostats are similar in all respects however, the main difference between them lies in their function, configuration, and typical application. The potentiometer is primarily used to adjust voltage while the rheostat is focused on regulating current flow.
Key FeaturesPotentiometersRheostatsPrimary UseVoltage Control(acts as a voltage divider)Current Control(varies resistance across the track)Number of TerminalsThey have three terminals (two fixed and one wiper)Mostly, they have two terminals sometimes three.Major ApplicationExtensively used in lower power circuits (e.g. Audio Control, Brightness control of Display).Extensively used for High-power circuits ( Speed control of motors, Light dimmer circuits)Principle of OperationAdjust voltage by dividing the resistive track.Adjust the current by varying the length of the resistive wire.Common UseVolume control and Sensor calibrationMotor Speed control and heater regulation. Trimpot or TrimmersA Trimpot or trimmer is a small potentiometer that is specially used for fine-tuning or calibration in the circuit. They are also known as preset resistors and are often set once during initial setup and are only adjusted by experts or for fine adjustment in the circuit.
Normally trimmers can be adjusted using a screwdriver. They can be of single-turn or multi-turn types. Single-turn is used in cases where a resolution of one turn is sufficient, however, when extreme fine-tuning is necessary multi-turn trimmers are preferred.
Non-Linear ResistorsTill now, among the different types of resistors, we have covered linear resistors. Now, lets talk about Non-linear resistors.
Non-linear resistors are types of resistors whose value does not remain constant but varies with changes in voltage, current, temperature, or other environmental conditions. Unlike linear resistors, non-linear resistors do not follow Ohm's law and exhibit a more complex relationship between current and voltage. There are many types of Non-linear resistors however most common types are :
As the name implies Varistor is composed of two words: variable and resistors ' so varistors are a type of voltage-dependent resistors. Resistance of the varistor decreases with the increase in voltage. In case of excessive voltage, the resistance drops drastically. This behavior makes them most suitable for surge protection and voltage clamping in power supplies.
The most common types of Varistors are
Thermistors are a special type of resistors whose resistance changes significantly with temperature variations. The word thermistor is composed of two words 'thermal' and 'resistors'.
So, in simple language, we can define a thermistor as a type of resistor whose resistance value is directly influenced by the temperature. Thermistors are further of two types:
PTC thermistors have a positive temperature coefficient which means their resistance increases non-linearly with the temperature rise, however, NTC thermistors have a negative temperature coefficient which means their resistance decreases non-linearly with the temperature rise.
Major Application of ThermistorsTemperature Monitoring
Thermistors are extensively used in digital thermometers or temperature-measuring devices as they are sensitive to changes in temperature.
Fire Alarm
Since the resistance of the thermistors is influenced by the change in temperature, this feature of the thermistor can be utilized in developing Fire Alarm circuits.
Over Current Protection
When the current exceeds a certain limit through an electronic circuit or devices, it generates heat. The thermistor can be used to detect such overcurrent and can be used as protection in the circuit to prevent over-exceeding of the current.
Temperature Control
These thermistors can be used to control the heating element to maintain preset temperature and when it exceeds the set limit it breaks the supply to re-establish the original preset temperature.
Photo Resistor or LDR (Light Dependent Resistors)Photo Resistors are also known as Light Dependent Resistors(LDR). As the name suggests, these types of resistors are responsive to the intensity of light. As light intensity increases, the resistance of such resistors decreases, and as light intensity decreases the resistance of such resistors increases in a non-linear fashion. In simple words, they show a negative correlation with the light intensity.
Major Application of LDRAutomatic Lighting Systems.
LDRs are responsive to the intensity of light. This feature of LDR can be used to develop an automatic street lighting system. The lamp will glow as soon as the intensity of the light decreases and switch off when the intensity of light increases.
Brightness Control
They are also used in different gadgets to automatically adjust the brightness of the display according to the surroundings.
Solar Tracking
LDRs are also used in devices that need to track the position of the sun and are frequently used in devices for such applications.
Important Parameters of ResistorsWe have gathered a lot of information about types of resistors, now let's see some of the important parameters of resistors before going into summary guidelines on the selection of resistors.
It is always the best approach to refer datasheet of resistors before choosing resistors for a particular application. However, for general applications, it is essential to look for some of the essential key parameters to ensure compatibility and performance. Some of the most important parameters of resistors are:
Choosing the right resistor for a particular task can be challenging. Since there are different types of resistors each with diverse construction materials and characterstics. Several factors need to be considered while choosing the right resistor for a particular project. Here, is a general guideline on how to choose the right resistor among the different types of resistors for a particular project.
Since, we have studied about different types of resistors, there arrises great confusion on how to choose perfect resistors among different types of resistors. In this article we have discussed about different types of resistors their manufacturing process and uses. From fixed resistors like carbon composition and metal film resistors as well as variable resistors like potentiometers and presets. We have studied about different types of resistors which operates in linear and non-linear fashion.
In addition, we have also studied about non-linear resistors like LDR, Thermistor, and Varistor. There are different factors that need to be taken in to consideration while making a proper choice among different types of resistors. We have studied all of them in detail and also listed a table for quick reference. By considering all these factors like resistance value, its typical use and application purpose we can ensure optimal choice among different types of resistors and ensure that the performance and realibility of our circuit is meet.
Release: -03-28, Update: -08-24, M.P.
Carbon film resistors, commonly called "carbon resistors," use a carbon-based baked film. They have the lowest cost and are available in a wide range of resistance values. Since their temperature coefficient is not very good, they are not used in applications requiring high accuracy. Carbon film resistors have become the mainstream type of general resistors due to their low cost and performance aspect.
Solid resistors use a baked kneaded mixture of a carbon-based resistive material and ceramic, etc., as the resistive element. These resistors have the feature of being robust and capable of being used in harsh conditions. Ultra-small resistors such as 1/16 W types can be produced, and in addition, a wide range of resistance values can be covered. However, from the cost aspect and overall characteristics aspect, carbon film resistors are better.
There are two types of metal film resistors: Thick film types in which the resistive element is a heated and fired metal-based paste, and thin-film types that use a metal vapor deposition film as the resistive element. They have relatively high accuracy (around ±1%) and better characteristics than carbon film resistors. However, they are somewhat expensive and cost 2 to 3 times as much as carbon film resistors.
Metal oxide film resistors use a film in which metal oxides are mixed into the resistive element. They are used in relatively intermediate power applications of around several watts, and are inexpensive. The temperature characteristics are inferior to metal film resistors at about ±350 ppm/°C, which is not very good.
Wire-wound resistors are resistors made by winding a thin metal wire around a ceramic bobbin. Since the structure of winding a wire around a bobbin is the same as a coil, these resistors have an inductance.
A resistor network is a type of composite component consisting of several resistors in a single package. It has the merits of reducing the number of components, saving labor, having high density, etc.
A variable-resistance resistor (trimmer) which is intended to be adjusted in the factory. It can be adjusted by turning with an adjustment screwdriver.
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