What is a Resistor? Overview, Types and Applications

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Resistors are electronic and electrical components that have a specific, always no-changing electrical resistance. The resistor’s resistance controls the flow of electrons through a circuit. They are passive components. They only consume power, cannot generate it. Resistors are typically used in circuits where they complement active components like op-amps, microcontrollers, and other integrated circuits (ICs). Typically, resistors are added to perimeter current, divide voltages and pull-up I/O lines.

Various resistors are used in massive quantities in manufacturing electronic equipment. Actually, the resistor is perhaps the most common type of electronic component used in electrical and electronic applications.

There is a big number of various types of resistors that can be bought and used. These different resistors’ properties vary, and it helps obtain the correct type of resistor for any given design to make sure that the best performance is obtained.

Although many resistors will work in various applications, the type of resistor can be vital in some cases. Consequently, it is necessary to know about the different resistor types and how applications each type of resistor can be used.

What is a resistor?

The resistors are used in practically all electronic circuits and several electrical ones. Resistors, as their name specifies, resist the flow of electricity, which is key to the most operation of most circuits.

There are two vital circuit symbols are made to identify the resistors. The firstborn one is still widely used in North America and consists of a jagged line representing the resistor’s wire. The further resistor circuit symbol is a small rectangle shape.  This is frequently termed the international resistor symbol, and it is more widely used in Europe and Asia.

Overview of a Resistor

  • A resistor regulates electrical current flow in the electronic circuit. Resistors provide a specific voltage for an active device, such as a transistor.
  • In a DC circuit, the current through a resistor is inversely proportional to its resistance and directly proportional to the voltage across it. In the AC circuits, this rule also applies as long as the resistor does not contain inductance or capacitance. This is the well-known Ohm’s Law.
  • The resistors are manufactured in a variety of ways. The most familiar type in electronic devices and systems is the carbon-composition resistor. Fine granulated carbon (graphite) is mixed with clay and hardened. The resistance depends on the proportion of carbon to clay; the higher this ratio, the lower the resistance.
  • Another type of resistor is made from winding Nichrome or similar wire in an insulating form. This component, called a wire-wound resistor, can handle higher currents than a carbon-composition resistor of the same physical size. However, because the wire is wound into a coil, the component acts as inductors and exhibiting resistance. This does not affect DC circuits’ performance but can have an adverse effect on AC circuits because inductance renders the device sensitive to frequency changes.

There are many different types of resistors as well. Some are for different applications like being used as variable resistors, and others are used for surge limitation while others provide a variable resistance with temperature changes.

Even though the component’s actual resistance is of paramount importance. Other characteristics also need to be taken into attention. Power dissipation, inductance, thermal stability, noise, and many other characteristics may all have a bearing on the operation of the circuit in which the resistor is used.

Various materials and different kinds of structures within the resistor can have an important impact. Thus, when selecting a resistor to be used, these characteristics must also be taken into consideration.

The electrical resistance of a resistor is calculated in ohms. The symbol for an ohm is Ω – the Greek capital omega.

The fundamental distinction of resistor types

The first significant categories into which the different types of resistors can be fitted is whether they are fixed or variable. These different resistor types are used for various applications:

       Fixed resistors –

Fixed resistors are most widely used in different applications. They are used in electronics circuits to set the right conditions in a circuit. Their values are determined during the circuit’s design phase, and they should never need to be changed to “adjust” the circuit. There are many different types of resistor which can be used in other circumstances, and these different types of the resistor are described in further detail below.

      Variable resistors –

These resistors consist of a fixed resistor element and a slider that taps onto the main resistor element. This gives three connections to the component: two connected to the fixed factor, and the third is the slider. In this way, the piece acts as a variable potential divider if all three connections are used. It is possible to connect to the slider and one end to provide a resistor with variable resistance.

Carbon film preset potentiometer Variable resistors and potentiometers are widely used for all forms of control: – everything from the volume controls on radios and sliders in audio mixers to a host of areas where variable resistance is required.

Potentiometer & variable resistor are components where a fixed resistor A variable resistor is effectively the same but with the slider linked to one end of the resistor to provide a proper variable resistance.

There are several different types of fixed resistor:

The resistors also suffered from a large and erratic irreversible change in resistance due to heat or age. In addition to this, the granular nature of the carbon and binder leads to high levels of noise being generated when the current flowed.

  • Carbon film –

This type of resistor was introduced during the early days of transistor technology when power levels tended to be lower.

  • Carbon film resistor –

A carbon film resistor is formed by “cracking” a hydrocarbon onto a ceramic former. The resulting deposited film had its resistance set by cutting a helix into the film. This made these resistors highly inductive and of little use for many RF applications. They exhibited a temperature coefficient of between -100 and -900 parts per million per degree Celsius. The carbon film is protected either by a conformal epoxy coating or a ceramic tube.

  • Metal oxide film resistor –

This type of resistor is now the most widely used form of the resistor. Rather than using a carbon film, this resistor type uses a metal oxide film deposited on a ceramic rod. As with the carbon film, the resistance can be adjusted by cutting a helical groove. Again, the film is protected using a conformal epoxy coating. This type of resistor has a temperature coefficient of around + or – 15 parts per million per °Celsius, giving it a far superior performance to that of any carbon-based resistor. Additionally, this type of resistor can be supplied to a much closer tolerance, 5% or even 2% being standard, with 1% versions available. They also exhibit a much lower noise level than carbon types of resistors. However, it has mainly been superseded but the metals film resistor.

Applications of Different Resistors

Resistors are in just about every electronic circuit ever. Here are a few examples of circuits, which heavily depend on our resistor friends.

LED Current Limiting

Resistors are key in ensuring LEDs don’t blow up when power is applied. By connecting a resistor in series with an LED, the current flowing through the two components can be limited to a safe value.

It is repeatedly called a ballast resistor. The ballast resistor is used to limit the current through the LED and to prevent that it burns. If the voltage source is equal to the voltage drop of the LED, no resistor is required.

Voltage Dividers

A voltage divider is a resistor circuit that turns a large voltage into a smaller one. Using just two resistors in series, an output voltage can be created that’s a fraction of the input voltage.

Voltage dividers are convenient for reading resistive sensors, like photocells, flex sensors, and force-sensitive resistors. One-half of the voltage divider is the sensor, and the part is a static resistor. The output voltage between the two components is connected to an ADC converter on a microcontroller (MCU) to read the sensor’s value.

Pull-up Resistors

A pull-up resistor is widely used to bias a microcontroller’s input pin to a known state. One end of the resistor is connected to the MCU’s pin. The other end is allied between  5V or 3.3V.

Without a pull-up resistor, inputs on the MCU could be left floating. There’s no guarantee that a floating pin is either high (5V) or low (0V).

Pull-up resistors are frequently used when interfacing with a button or switch input. The pull-up resistor can bias the input pin when the switch is open. It will give protection to the circuit from a short when the switch is shut down.

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