Resistors:

What is a resistor?

Resistors are popular components in electrical networks, electronic circuits and electronic equipment. They are dispensable within integrated circuits.

In electronic circuits, a resistor is a passive two-terminal electrical component that implements electrical resistance. They reduce current flow, adjust signal levels, divide voltages, active bias elements, terminate transmission lines etc. 

Resistors are electronic components with a specific, never-changing electrical resistance that can limit the flow of electrons through a circuit.

These passive components can only consume power to complement active components like op-amps, microcontrollers and other integrated circuits. Usually, resistors are to limit current, divide voltages and pull up I/O lines.


How is a resistor made?

The choice of material technology is specific and varies according to its purpose. It is usually a trade-off between costs, precision and other requirements. 

For example, carbon composition is an ancient technique with low precision but is still used for specific applications where high-energy pulses occur. Carbon composition resistors consist of a body made of fine carbon particles and a non-conductive ceramic. Generally, the carbon film technique has a better tolerance with a non-conductive rod and a thin carbon film layer. The spiral cut is to increase and control the resistance value. 

Metal and metal oxide films are becoming more popular these days as they have better stability and tolerance. Moreover, they are less affected by temperature variations. They are carbon film resistors constructed with a resistive film around a cylindrical body. The metal oxide film provides better durability. 

Wirewound resistors are considered the oldest type with high precision and high power applications. They are durable, accurate and can have a low resistance value. The only drawback is that at high frequencies it suffers from parasitic reactance. 

Metal foil resistors are the choice for high precision and stability as they are made from cementing a special alloy cold-rolled film onto a ceramic substrate.


What are different types of resistors?

Resistors can be classified based on construction type or resistance materials. Some popular types of resistors are listed below:

  • Fixed resistors 

  • Variable resistors, such as Potentiometer, Rheostat and Trimpot.

  • Resistance by physical quantity: Thermistors, Photoresistor, Varistor, Magneto resistor and Strain Gauges.

Another way to categorise resistors is by material and manufacturing process, including carbon composition, carbon film, metal film, metal oxide film, wire wound and foil.

Resistors will also come in one of two termination types: through-hole or surface-mount. The abbreviations for these resistors are either PTH (plated through-hole) or SMD/SMT (surface-mount technology or device).


How does a resistor work?

While making electric or electronic circuits to perform particular tasks, it is crucial to introduce a precise amount of resistance by simply adding a resistor. 

Inside a resistor, the number of copper turns will precisely control the resistance: the higher the resistance is, the more copper turns and the thinner the copper is. Carbon-film resistors are cheap to make with spiral patterns of carbon instead of copper winding. We can see this type of smaller-value resistor in lower-power circuits. Typically, at higher operating temperatures, wire-wound resistors are more stable and more precise.

A resistor's purpose is to protect the components and the circuits from overheating and other damage caused by high current. Without proper resistance, LEDs would burn out quickly.

The resistors usually come with different color codes with 4, 5, or 6 bands. These bands indicate the value and tolerance of a resistor.


What are the applications of a resistor?

High-power resistors can dissipate many watts of electrical power as heat, which is helpful as a part of motor controls, power distribution systems or test loads for generators. Fixed resistors have resistances, which will slightly change, adjusting to its operating voltage, time or temperature. Variable resistors can adjust circuit elements, such as lamp dimmer volume control or sensing devices for heat, light, humidity, force or chemical activity.


Who manufactures resistors?

Some of the most trusted brands that manufacture resistors are Vishay, TE Connectivity, Murata, KOA Speer, ROHM, Yageo, and Panasonic. 


Where to buy resistors?

Purchasing professionals can easily acquire resistors from the manufacturer's websites. However, to have a better price or a quicker service, electronic distributors would be a better choice. BD Electronics Ltd. is a trusted European distributor of electronic components, providing all types of products with prompt delivery and reasonable price.

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