The Basics of Resistors

Resistors are one of the most common components for electronic circuit assembly, and they come in many shapes and forms to provide a variety of properties and characteristics that may benefit differing applications. In their most simplistic form, resistors are passive electronic parts featuring two-terminals, and they are used to provide electrical resistance to a circuit. While seemingly simple, the variations in resistor types allow them to take on different roles such as reducing current flow, terminating transmission lines, dividing voltages, adjusting signal levels, and much more.

While different resistors will often be characterized by their ohmic value or other performance properties, the first major categories that serve to separate distinct types from one another is whether a resistor is fixed or variable. Fixed resistors are the most common types found within electronic circuits, and they feature set resistance values that are only slightly affected by conditions such as temperature or operating voltages. With variable resistors, circuit elements can be adjusted with the use of a slider.

Carbon composition resistors are an early fixed resistor type that was once one widely used, and they are often constructed by embedding a solid cylindrical resistive element with wire leads or end caps. To produce the resistive element, powdered carbon is mixed with a ceramic or another insulating material, and a resin is used to bind everything together. To protect the resistor’s body, paint or plastic is used to create a shell and color-coating may be implemented to denote the component’s value. As more advanced resistor types have been released over the years, the carbon composition resistor has become less common due to its inability to surpass the performance and cost of other types.

Carbon film resistors are those that are created by depositing carbon film onto an insulating substrate. With the resistive properties of carbon and a variety of shapes available, such resistors are capable of performing well on a wide range of resistance values. When compared to the carbon composition resistor, the carbon film type can operate with lower noise due to its optimal distribution of unbound pure graphite. With their ability to perform on a wider range of resistances, operating temperatures, and working voltages, such resistors are common to applications needing high pulse stability.

The metal oxide film resistor is a type with similar construction to the carbon composition resistor, though its materials consist of metal oxide film that has been deposited on a ceramic rod. With a superior temperature coefficient, close tolerances, and low noise levels, the metal oxide film resistor has currently established itself as the most widely used type.

Metal film resistors are those that use nickel chromium or other metal film materials for deposition. Due to its similar construction to the metal oxide film type, the metal film resistor is capable of achieving similar performance. With its properties and construction, the metal film resistor is most often used in applications requiring a leaded resistor.

When working with high power applications, the wire wound resistor is a reliable choice due to its characteristics. To produce such electronic parts, a metal wire of nichrome or another material is wound around an insulating core before having its ends soldered or welded to caps or rings. With a protective layer of baked enamel, molded plastic, or paint, the resistor is completed. Due to their materials and construction, such resistors are capable of operating in extremely high temperatures. With their winding, however, wire wound resistors suffer in applications that have higher frequencies.


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December 23, 2020

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