Fixed resistor

 
Fixed resistor

What is a fixed resistor? Fixed value resistors have a defined ohmic resistance and are 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. Fixed resistor definition A resistor having a fixed, defined electrical resistance which is not adjustable. 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. Some common types of fixed resistors are displayed below. For a complete overview of the basic properties and applications of standard resistors, take a look at the article ‘What is a resistor‘. Identifying fixed value resistors In the following table an overview of general purpose resistors is given. The types listed here are among the most used resistors in general. 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 [… read more]

Resistor types

 
Resistor types

There are a lot of different resistor types, all with their own applications, characteristics and construction. This page lists the different resistor types which are described on the resistor guide. Fixed resistors The fixed resistor type is the most common resistor, when people talk about a resistor they most probably mean a fixed resistor. The picture to the right shows an axial carbon film resistor, the most common type. Fixed resistors have a constant resistance value. Different resistor materials are used for fixed resistors. For all resistor types the used materials has influence on the resistor properties like the tolerance, cost and noise. Fixed resistors are available in axial and SMD packages. Variable resistors There are several variable resistor types, their general property is that the resistance value is adjustable. Most variable resistors are adjusted by mechanical movement (linear or rotary). When they are used as a variable voltage divider, they are called potentiometers. When they are used as a variable resistance to control the current in a circuit, they are called rheostats. Digital potentiometers are controlled electronically instead of by mechanical action. In general variable resistors have a higher tolerance of 20% compared to fixed resistors where 5% is the most common. Thermistors Thermistors are resistors of which the resistance changes significantly when temperature changes. Different thermistor types exist, the two most common types are the NTC and PTC thermistor. NTC thermistors decrease in resistance when the temperature rises, while PTC thermistors increase in resistance when the temperature rises. Thermistors are often used as temperature sensors or thermal protection devices. Varistors Varistors have a non-linear resistance which is dependent on the voltage over the varistor. Above a certain threshold voltage the resistance of a varistor drops very fast. Different varistor types exist, but nowadays the MOV varistor is the [… read more]