Table of Contents
Resistors may be defined as a passive two-terminal electrical component that is known for implementing electrical resistance as a circuit element. Resistors are used for reducing the flow of current in electronic circuits, adjusting signal levels, dividing voltages, and terminating the transmission lines.
The high-power resistors are known for dissipating watts of electrical power in the form of heat which may further be utilized as motor controls, test loads in generators, and power distributing systems. Fixed resistors are known for having resistances that change slightly with time, operating voltage, and temperature.
The variable resistors are the ones that may be used for adjusting the circuit elements such as a lamp dimmer or a volume controller. These may further be used for sensing devices for light, force, heat, chemical activity, or humidity.
Resistors are basically commonly known elements of electronic circuits and electrical networks and are ubiquitous in electronic equipment. The practical resistors are the discrete components that may be composed of different compounds and forms.
These are known for being implemented within the integrated circuits. In resistors, resistance specifies the electrical function. The common commercial resistors are known to be manufactured across a set of more than 9 magnitude orders. The resistance’s nominal value is known for falling within the area of manufacturing tolerance which is indicated on the component.
Classification of Resistor
Resistors are known for being commonly used in electronic circuits; these are mainly fixed resistors and potentiometers. On the basis of different processes and materials, fixed resistors may be divided into solid core resistance, special resistor, metal wire wound resistor, and film resistors. Let’s understand the classification of resistors in detail in the following types of resistors.
Types of Resistor
There are various types of resistors for electronics constructor which are available to choose from. These are present in different sizes ranging from large wire-wound power resistors to tiny surface-mount chip resistors.
There are different types of resistors that are produced in various forms as a result of their specific characteristics and accuracy that suit different areas of its application such as high current, high voltage, high stability, and so on. These are used for general purposes where their characteristics don’t create a problem.
A resistor is known for installing electrical resistance in the electronic circuit. These are basically two-terminal passive components which are of two types namely fixed resistors and variable resistors.
Types of resistors commonly used include carbon film resistor, carbon resistor, metal film resistor, light-dependent resistor, non-linear resistor, thermistor, carbon composition resistor, carbon film potentiometer, wire wound resistor, and wire-wound potentiometer.
Fixed Resistors
Resistors with resistance that doesn’t change with any change in the temperature or voltage may be termed fixed resistors. These resistors are available in different sizes and shapes. Any resistor providing constant resistance in different environments is considered an ideal fixed resistor.
Variable Resistors
A resistor whose electric resistance value may be adjusted is termed a variable resistor. It may be considered as an electromechanical transducer which generally works by a sliding wiper over the resistive element. A potentiometer is a variable resistor used as a potential divider by bringing in use 3 terminals.
Metal Film Resistor
A metal film resistor or a carbon film resistor is constructed as a result of the deposition of a thin film constituted of a conductive material such as a metal or pure carbon on an insulating core.
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The required resistance value of these resistors may be easily obtained by cutting helical grooves of pitch along the length or trimming the thickness layer. The metallic contact caps are fitted at resistor’s both ends. The caps are generally in contact with the helical grooves or conductive film with the lead wire welded to the caps’ end.
Light Dependent Resistor
An LDR or light-dependent resistor varies in resistance depending on its intensity of falling light. It is made up of cadmium sulfide which comprises a few electrons when it is not illuminated.
Every time a ray of light falls, electrons are ejected leading to an increase in its conductivity. Therefore, it is known for offering low resistance each time the light falls and delivering high resistance in the dark.
Non-Linear Resistor
Non-linear resistors or varistors are popular for having the characteristic curve which is a non-linear V-I. Its resistance is neither uniform nor it obeys the ohms law. These are made up of materials consisting of zinc oxide and silicon carbides. These are generally divided into three types which are silicon carbide disc type varistor, silicon carbide rod type varistor, and zinc oxide type varistor.
Thermistor
Thermistor refers to a thermal resistor. The resistance value of these resistors changes with the temperature change. Mostly, thermistors are known for having a negative temperature coefficient which means that there is a downfall in their resistance with the increase in temperature.
Thermistors are made up of semiconductor materials and are capable of providing a few megaohms. They are used for the purpose of detecting minor temperature changes. When the temperature changes, no matter how small it is, a large change occurs in the resistance value.
Carbon Composition Resistor
A carbon resistor or carbon composition resistor is a very popular and commonly used resistor. Constructed of a carbon clay composition, covered with a plastic case, these are low in cost and are constructed very easily. The lead of this type of resistor is made up of tinned copper.
Some of its main advantages include its easy availability, durability, and its low cost. This type of resistor exists in a wide range of values beginning from 1 Ω to 22 Mega Ω. These resistors have various color bands on their cylindrical body representing color codes for the resistance value of resistors in addition to their tolerance range.
Carbon Film Potentiometer
A carbon film potentiometer is an electronic component that is a variable resistor. It is used as a voltage divider which is known for providing variable output voltage. This potentiometer is known for using carbon as a resistive element.
There are various types of it such as ceramic type and the wire wound type which are based on the usage of distinct materials on the resistive element.
Wire Wound Resistor
A wire of constantan or manganin is wound around an insulated material cylinder in a wire wound resistor. The temperature coefficient of resistance of constantan and manganin is nearly zero. This is why the temperature resistance variation of these resistors is insignificant.
In these resistors, the wounded wire is protected with an insulating cover such as baked enamel. This cover which is made up of an insulating heat resistible material resists the effect caused by temperature variation. These resistors are available in different sizes and ratings which becomes possible with the use of diverse diameters and lengths of the wire.
Wire Wound Potentiometer
It is similar to a slide-wire potentiometer, the only difference being that the resistance wire is wound on a form with contact made with a slider. The wire-wound potentiometer is wound on a ring skeleton using a resistance wire. It is basically characterized by a small resistance range and huge power.
How Resistors Work
It’s time to read about how resistors work, let’s get started. The main work of a resistor present in an electronic or electrical circuit is to “resist” which is why it is termed as a resistor. It not only resists but also regulates or sets the flow of the current or electrons via them by utilizing various types of conductive material they are composed of.
These may be connected in various types of series and parallel combinations for forming resistor networks. These further act as voltage dividers, voltage droppers, or current limiters within the circuit. Resistors are known as passive devices as they have no amplification or power source and mainly reduce or attenuate the current or voltage signal going through them.
This reduction results in the loss of electrical energy as heat because the resistor resists the electron flow.
Uses of Resistors
Resistors are mainly used for controlling the current flow. The electrons present in a resistor have collisions with ions which is known for slowing down the electricity flow. It further produces heat and lowers the current. If a resistor is known for its high resistance then this means that its current flow is less with the available voltage.
Some of the areas of use of resistors include dividing voltage, LEDs, transistors, heating, circuit functions, frequency, and timing. Let’s read about all these in detail.
Application in Diving Voltage:
The diving voltage works when the components are required to work with voltage less than that supplied in the input voltage. The resistors connected in a series help in dropping the voltage across every single resistor in equal proportion. This assists the appliances that are used for working in such conditions.
Usage for Heating:
During current conduction, heat is generated which is why resistors are used in the toaster, electric stove, heater, microwave, and other heating appliances. It has been observed that the metal filament glows white-hot in a light bulb as a result of the high temperature. This high temperature is produced from the resistance when the electricity passes through it.
Application in Circuit Functions:
There are different types of resistors that perform work in accordance with the usage range. The resistance may be set by using a feature that resembles a knob. The change in resistance gets affected by the flow of current present inside the circuit. This resistor is used for controlling the motor speed, amplifier loudness, and the pitch of a musical tone.
Particular Timing and Certain Frequency Function:
Resistors are used in electronic sirens, light flashers, blinking lights in airplanes, and tall towers which all act as a measure for collision avoidance. These work on the principle of current filling up to a specific time leading to light discharge.
Here, the resistors are known for deciding the amount of current which is to be passed in accordance with the allotted time. If an increase in the resistance happens, the discharge time of the current in the circuit increases as well.
Application in Transistors and LEDs
If too much current passes through a transistor or LED, it might be dangerous as they are considered sensitive to the electric current. In a circuit, the use of resistors helps the transistors and LEDs along with various semiconductors to function in the required current range that is ideal for them.
Resistor Colour Codes
The wires and components are coded with colors so that the values and functions may be easily identified. The resistor color codes utilize colorful bands which quickly identify the resistive value of resistors. Not only this, the tolerance percentage of the resistors along with the physical size of the resistor indicates the wattage rating.
Generally speaking, the tolerance, resistance value, and wattage rating are printed on the resistor body as letters or numbers. This happens when the body of resistors is big enough to easily read the print such as in the case of large power resistors. In cases of the small resistor, the print is small too and cannot be read easily. Therefore, the specifications are shown in a different manner.
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The colors red, blue, green, brown, and violet may be used in the form of tolerance codes on five-band resistors. These resistors use a color tolerance band. Any blank band or the one which is 20% blank is used with a 4-band code comprising of 3 colored bands in addition to a blank band.
A yellow violet orange-gold color code is 47 kΩ having a tolerance of +/- 5%. A green-red gold silver color code is 5.2 kΩ having a tolerance of +/- 10%. A white violet black color code is 97 kΩ having a tolerance of +/- 20%. When three color bands are visible on a resistor, it is a 4-band code with a 20% blank space.
An orange black brown violet color code is 3.3 kΩ with tolerance of +/- 0.1%. A brown green grey silver red color code is 1.58 kΩ with a tolerance of +/- 2%. A blue brown green silver-blue color code is 6.15 kΩ with a tolerance of +/- 0.2%. Hope you now have an idea of what resistor color codes are all about.
Advantages of Resistors
Resistors are small which makes carrying it easily from one place to the other. They are usually cheap and can be easily replaced. They do not depend on any of the external sources of voltage which is why any energy or external voltage is not required for operating resistors. Here are some more advantages of resistors.
The resistors that are composed of carbon are smaller in size in comparison to the wire-wound resistors. It offers a wide range of resistance range and is considered the cheapest one. They are known for delivering fine RF performance.
Disadvantages of Resistors
Let’s read about some disadvantages of resistors. Resistors are known for having high resistance which opposes the large volume of electric current. This is why a large amount of energy gets wasted in the heat form. The resistors that are composed of carbon have a high tolerance with no precision. Such resistors may be heated very easily and crackdown when soldered.
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