Fundamentals of Resistor and Electrical Resistance in Electronic Devices and Power Supply Circuits
Resistor Definition:
A resistor, or an electrical resistor, is a two-terminal passive electronic device that provides a predetermined amount of resistance to an electrical circuit. Its main objective is to resist or restrict the passage of electric current, thus helping to control and regulate the current in different sections of a circuit. Resistors are basic electronic components in analog and digital systems, serving significant functions like regulation of current, voltage division, active device biasing like a transistor, and protection of components from voltage surge or current bursts. Resistors find applications across simple LED-based circuits to very sophisticated microprocessors, and for this reason alone, they represent one of the most ubiquitous components in electronic development.
A Resistor can be recognized by its four-band color pattern as shown in the image below:
● Band A depicts the 1st significant digit.
● Band B indicates the 2nd significant digit.
● Band C symbolizes a Multiplexer.
● Band D defines the % of Tolerance.
Electrical Resistance Definition:
The ability of an electrical conductor to create obstruction in electric current flow is known as electrical resistance, which signifies the fact that higher the resistance value lower will be the amount of current passing through the material.
Resistance is denoted by capital (R) and is measured in Ohms (Ω). According to Ohm’s law, the current flowing through a conductor is directly proportional to the potential difference (voltage) across it, assuming the temperature and other physical conditions remain constant.
V = IR
Where,
V = Potential difference across the conductor (measured in Volts)
I = Current flowing through the conductor (measured in Amperes)
R(Resistance) = Constant of proportionality (measured in Ohms).
Difference between Resistor and Resistance:
● The Resistor is a two-terminal passive electrical or electronic component designed to restrict the current flow, whereas Resistance refers to the property of the material opposing the flow of current.
● A resistor is constructed from discrete devices having specific resistance properties, whereas Resistance signifies the extent to which a material obstructs the flow of electrons.
Electrical Resistor Circuit Symbol:
Electrical Resistors consist of two main circuit symbols. In the USA, the ANSI standard is commonly used which represents a fixed resistor as a zigzag line. The international IEC symbol is a rectangular shape with leads at each end widely used in Europe and Asia.
Types of Resistors
According to the property of linearity, resistors can be classified into two types:
● Linear Resistors
● Non-Linear Resistors
According to the value of resistance, Linear Resistors are categorized into the following two types i.e., Fixed Resistors and Variable Resistors
Linear Resistors
Linear Resistors are the most widely used resistors in electronic circuits, which adhere to Ohm's Law and provide a linear relationship between voltage and current.
Linear Resistors can be subdivided into Fixed Resistors and Variable Resistors.
1. Fixed Resistors: Fixed resistors belong to a class of Linear resistors, following a constant range of resistance values. However, their temperature coefficient is very large, resulting in less stability.
Types of Fixed Resistors:
● Carbon Film Resistor, also known as carbon composition resistance, which is made from a mixture of carbon and ceramic, and is less accurate but cheaper.
● Wire Wound Resistor, these resistors are constructed by coiling the metal wire around a ceramic core, and they provide high strength with high accuracy.
● Metal Film Resistor , made with a thin metal film on a ceramic substrate, provides high precision and stability.
● Foil Resistors , use metal foil on a ceramic substrate, which offers excellent precision and stability.
2. Variable Resistors: Variable Resistors exhibit the property to modify the resistance value mechanically. Potentiometers and Rheostats tend to be prominent instances of variable resistors, enabling resistance adjustments within a specific range. Applications obligating variable resistance, such as radio receivers, sensor applications, and volume controls, are the primary uses for variable resistors.
● Potentiometer – A dial or knob is commonly employed for regulating such types of resistors. They comprise of three terminals along with a moving contact connected to a control shaft. By twisting the control shaft, the voltage across the resistor can be changed. Applications include transducers and audio/visual equipment.
● Rheostat – Wire-wounded resistors serve as the core of the resistor and these tapped resistors make use of sliding contact for voltage adjustments. They serve their purpose in transducers and audio-video equipment.
● Trimmer Resistor – By rotating a screw, a trimmer resistor can be precisely "trimmed" to the desired resistance.
Non-Linear Resistors
Ohm's Law does not apply to nonlinear resistors. The resistance of nonlinear resistors changes with variations in voltage, current, or other factors like temperature or light, causing a nonlinear relationship between the two variables.
Examples of Non-Linear Resistors include:
● Thermistors – Thermistors are temperature-sensitive resistors where the resistance tends to be a function of temperature. Types include NTC (Negative Temperature Coefficient) and PTC (Positive Temperature Coefficient).
● Varistors – the resistance is a function of voltage.
● Light Dependent Resistor (LDR) or Photo Resistors – the resistance is a function of light level.
● Magneto Resistors – Also known as Magnetic Field Dependent Resistors, where the resistance is a function of the magnetic field.
● surface mount resistors – The primary function of an SMR is to limit or regulate the current flow, reduce voltage levels, and divide voltages.
The unikeyicElectronics website sells most types of resistors, including Surface-Mount Resistors, Photo Resistors, Varistors, PTC and NTC Thermistors, Through-Hole Resistors, Potentiometers, and other fixed resistor types. The website also offers additional resistor varieties.
Resistor Color Code
To find the value of any resistor or determine the value of the resistance, we use various color-coded bands known as the Resistor Color Code.
Mnemonic of Resistor Color Code: BB ROY of Great Britain has a Very Good Wife
Applications of Resistors
A few common uses of resistors are listed below:
● In Differential Amplifiers, the resistor is used to balance input and output impedances.
● The resistor is employed in producing heat from electrical power in resistance heating.
● Resistors can be used to match the impedance of different parts of a circuit to minimize signal reflection.
● Resistors are also employed to safeguard sensitive electronic components such as transistors, LEDs, etc., from overcurrent and overvoltage.
