Resistors are one of the most widely used components in electronic circuits – there are many different types of resistors available having different properties and used in different ways in different circuits.

Resistors of every type are employed in huge quantities in producing equipment.

In fact, the resistor is probably the most common type of electronic component used in electrical and electronic circuits.

There is a large number of different types of resistors that can be bought and used. The properties of these different resistors vary, and it helps to obtain the right type of resistor for any given design to ensure that the best performance is obtained.

Although several electrical devices can add a range of applications the kind of resistor is vital in some cases.

Accordingly, it’s necessary to grasp concerning the various electrical device varieties, and within which applications every style of an electrical device is used.

What is a resistor?

Resistors are used in virtually all electronic circuits and many electrical ones. Resistors, as their name, indicates resist the flow of electricity, and this function is key to the operation of most circuits.
There are two main circuit symbols used for resistors. The oldest one is still widely used in North America and consists of a jagged line representing the wire used in a resistor. The other resistor circuit symbol is a small rectangle, and this is often termed the international resistor symbol and it is more widely used in Europe and Asia.
more widely used in Europe and Asia.
Resistor circuit symbols
The unit or resistance is the Ohm, Ω and resistor values may be seen quoted in terms of Ohms – Ω, thousands of Ohms or kilohms – kΩ and millions of Ohms, megohms, MΩ. When written on circuits values like 10k may be seen meaning 10 kilohms, or 10 kΩ. The Omega sign is often omitted and the decimal point replaced by the multiplier: e.g. 1R5 would be 1.5 Ohms, 100R is 100Ω, 4k7 is 4.7 kΩ, 2M2 is 2.2MΩ and so forth.

Basic distinction of resistor types

The first major classes into that the various styles of resistance will be fitted is into whether or not they square measure mounted or variable.

These completely different resistance sorts square measure used for various applications:

 Fixed resistors:

Fixed resistors are by far the most widely used type of resistor. They are used in electronics circuits to set the right conditions in a circuit.

Their values square measure determined throughout the look section of the circuit, and that they ought to ne’er ought to be modified to “adjust” the circuit.

Their square measure {many completely different many various many alternative} styles of resistance which may be employed in different circumstances and these different kinds of resistance square measure delineate in additional detail below.

Variable resistors:

These resistors consist of a fixed resistor element and a slider that taps onto the main resistor element.

This gives 3 connections to the component: 2 connected to the mounted component, and the third is the slider.

In this method, the element acts as a variable resistance if all 3 connections square measure used.

It is doable to attach to the slider and one finish to supply a resistance 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 Strictly a potentiometer is a component where there is a fixed resistor that has a slider to provide a potential division from the voltage at the top. A variable resistor is effectively the same, but with the slider linked to one end of the resistor so that it provides a true variable resistance.

fixed resistor types

There are a variety of various kinds of mounted resistor:

Carbon composition: The carbon composition resistor is a type of resistor that was once very common – it was the main type of resistor, but are now seldom used

because newer sorts of resistance offer higher performance, they’re smaller and additionally cheaper.

Carbon composition resistors are formed by mixing carbon granules with a binder which was then made into a small rod.

This type of resistance was giant by today’s standards and suffered from an oversized negative temperature constant.

The resistors additionally suffered from oversized and erratic irreversible changes in resistance as a result of heat or age.

In addition to this, the granular nature of the carbon and binder leads to high levels of noise being generated when 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 The 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 created these resistors extremely inductive and of very little use for several RF applications.

They exhibited a temperature constant of between -100 and -900 elements per million per degree Celcius.

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 employing 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 in the film.

Again the film is protected employing a conformal epoxy coating.

This type of resistor has a temperature coefficient of around + or – 15 parts per million per °Celcius, giving it a far superior performance to that of any carbon-based resistor.

Additionally, this kind of resistance are often provided to a far nearer tolerance, 5% or even 2% being standard, with 1% versions available.

They also exhibit a much lower noise level than carbon types of resistor, however, it has mainly been superseded but he metal film resistor.

 Metal film resistor

 The metal film resistor is very similar to the metal oxide film resistor. Visually it is very similar and the performance is also comparable.

Instead of employing a metal compound film, this type of resistor uses a metal film as the name indicates.

Metals such as nickel alloy may be used.

Leaded metal film resistance The metal film resistance is that the kind that’s most generally used once a leaded resistance is required.

Wire wound resistor:

This resistor type is generally reserved for high power applications.

These resistors are created by winding wire with a better than traditional resistance (resistance wire) on a former.

The more expensive varieties are wound on a ceramic former and they may be covered by a vitreous or silicone enamel.

This electrical device kind is suited to high powers and exhibits a high level of reliableness at high powers together with a relatively low level of temperature constant, although this

will depend upon a variety of things together with the previous, wire used, etc.

As wire wound resistors are often intended for high power applications, some varieties are designed so that they can be mounted onto a heat sink to ensure that the power is dissipated into metalwork so it can be carried away.
In view of their wound nature, they are not suitable for operation above low frequencies, although by winding parts of the resistance wire in different directions the inductance can be reduced somewhat.

Surface-mount resistors

Surface mount technology, SMT is now the major format used for electronic components. They are easier to use in automated manufacturing, and they are able to provide very high levels of performance. SMT resistors utilize similar technologies to other forms but in a surface mount format.
Other types of resistors.

Whilst the bulk of resistors ar customary fastened resistors or variable resistors, there is a number of other resistor types that are used in some more niche or specialized applications.

 Light-dependent resistor/photoresistor

 Light-dependent resistors or photoresistors change their resistance with the level of light. They are used in a number of sensor applications and provide a very cost-effective solution in many instances.
Typical leaded light-dependent resistor Light-dependent resistors have a lag in the time taken to respond to light changes, but they are cheap and easy to use.
• Thermistor: As the name indicates, thermistors are heat sensitive resistors. The resistance of the thermistor varies with temperature. Some have a negative temperature coefficient, NTC thermistors, whilst others have a positive temperature coefficient, PTC thermistors.
• Varistor: Varistors are available in a number of forms. Essentially these electronic components vary their resistance with the applied voltage and as a result, they find uses for spike and surge protection. Often they may be seen described as Movistors, which is a contraction of the words

Metal Oxide Varistor.

Selection of leaded varistors Varistors are the devices that are widely used in surge or transient protected mains extension leads and used to protect computers. It should be remembered that each time the varistor receives a spike its properties change slightly.

Although resistors could also be thought of as straightforward natural philosophy parts to use, there are a number of parameters that need to be considered when choosing the correct resistor type.

Parameters apart from just the resistance are important.

Voltage face up to, power dissipation and therefore the actual sort of electrical device itself all has an effect on the performance.

With a variety of resistor types available, it is necessary to choose the correct type for any particular application. In this way, the best performance can be assured.



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