A resistor is having a fixed, defined electrical resistance which is not adjustable. Fixed resistors are the most commonly used resistors and in general one of the most used electronic components. Fixed resistors are available in axial leaded and surface mount packages as well as more customized packages depending on their application. While axial leaded resistors used to be the most used resistors, nowadays the advantages of surface mount devices make the SMD resistors the most popular. Microhm Electronics manufactures wide range of fixed resistors, including surface mount resistors, axial resistors, radial resistors and more.
 

 

Fixed resistor definition

In an ideal world a perfect resistor would have a constant ohmic resistance under all circumstances. This resistance would be independent of for example frequency, voltage or temperature. In practice no resistor is perfect and all resistors have a certain stray capacitance and inductance, resulting in an impedance value different from the nominal resistance value. The resistor materials have a certain temperature coefficient, resulting in a temperature dependency of the resistor value. The different resistor types and materials determine the dependency of the resistance value on these external factors. Depending on e.g. the required accuracy, power dissipation and noise requirements, the type and material of resistor are selected. 

 

Identifying fixed value resistors

The carbon film is the most common axial leaded resistor which is used for applications where a very good tolerance and temperature coefficient are not necessary. The metal film is the general axial leaded resistor of choice for higher precision applications. For high power applications wirewound resistors are often used, such as NUAL series from Microhm Electronics, the aluminium housing  is often used for power ratings from 10-250W. Surface mount or SMD resistors are in general constructed from thick or thin film material.

 

Fixed resistor symbols

The above resistor symbols are often used to depict resistors with a fixed value. The most used symbol is the international IEC resistor symbol displayed on the left but the American resistor symbol displayed on the right is also still used.