The Difference Between Fixed, Wirewound, Foil, and Semiconductor Resistors

Resistors are common electrical components found in circuitry, serving to implement electrical resistance. Resistors can play multiple roles within a circuit, commonly acting to reduce current flow, divide voltages, manage signal levels, bias active elements, terminate transmission lines, and much more. As a longstanding technology, a number of variations have come about to accommodate particular application requirements or needs. Wirewound, foil, and semiconductor resistors are three common types, each of which have their own unique construction and capabilities that benefit varying needs. In this blog, we will discuss each type, allowing you to best understand their design and applications.

A fixed resistor is a basic type of resistor component, featuring a designated electrical resistance that is unable to be adjusted. As a general category for varying resistors, common fixed types include carbon film, metal film, wirewound, and surface mount resistors. As each type will often have different characteristics that can benefit certain applications, it is important to be aware of the variations between each and how they may be used.

The wirewound resistor is a type that may be constructed by winding a resistive wire around a non-conductive core. Generally, the wire may be produced from Nichrome or Manganin alloy, while the core is a ceramic material or fiberglass rod. Once the wire has been wound, an insulating coating is placed over the component. While wirewound resistors are often considered to have low values of resistance, they are well capable of dissipating a large amount of heat and are optimal for high precision or high power applications. Wirewound resistors are also capable of featuring a tolerance level of 0.01%, though their tolerance is typically dictated by their resistance and will have a higher tolerance level for higher resistance levels. Frequency response and noise are another two important characteristics of resistor components, and the wirewound resistor is unable to optimally serve high-frequency applications though has low noise levels. With their robust construction and high reliability, wirewound resistors are most commonly found in high precision applications where they are bolted to a metal chassis with a metallic case or placed in a PCB mount arrangement.

Foil resistors are a type that are constructed through the cementing of a metallic foil onto a ceramic substrate. With the foil often being a few micrometers thick, foil resistors are commonly known to be the most stable and precise option out of the common types. Despite such benefits, foil resistors often lack high resistances and as such are limited in implementation for common circuits. Instead, they are typically relied on for high precision applications that are below 5 Watt. Other advantages of the foil resistor include their low noise and high frequency response. While optimal for certain high precision applications with limited resistance, they are not beneficial in regular circuits, high power applications, or areas where they may be exposed to harsh environments.

A semiconductor resistor is a type that is constructed through the deposition of a thin resistive film onto a ceramic substrate. To achieve a specific resistance value, laser systems are used to cut the resistive coating as needed. Each individual component may vary in its construction, sometimes featuring either a single resistor or an array. Additionally, they may also be referred to by other various names such as SMT resistors, IC resistors, or chip resistors. With their various characteristics, semiconductor resistor components are most beneficial for surface mount applications that are low power and high frequency.

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February 8, 2022

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