RESISTOR'S
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Resistors, ( R ) are the most fundamental and commonly used of all the electronic components, to the point where they are almost taken for granted.There are many different TYPES OF RESISTOR available for the electronics constructor to choose from, from very small surface mount chip resistors up to large wire wound power resistors.
The principal job of a resistor within an electrical or electronic circuit is to “resist” (hence the name Resistor), regulate or to set the flow of electrons (current) through them by using the type of conductive material from which they are composed. Resistors can also be connected together in various series and parallel combinations to form resistor networks which can act as voltage droppers, voltage dividers or current limiters within a circuit.
Resistors are what are called “Passive Devices”, that is they contain no source of power or amplification but only attenuate or reduce the voltage or current signal passing through them. This attenuation results in electrical energy being lost in the form of heat as the resistor resists the flow of electrons through it.
Then a potential difference is required between the two terminals of a resistor for current to flow. This potential difference balances out the energy lost. When used in DC circuits the potential difference, also known as a resistors voltage drop, is measured across the terminals as the circuit current flows through the resistor.
Most types of resistor are linear devices that produce a voltage drop across themselves when an electrical current flows through them because they obey Ohm’s Law, and different values of resistance produces different values of current or voltage. This can be very useful in Electronic circuits by controlling or reducing either the current flow or voltage produced across them we can produce a voltage-to-current and current-to-voltage converter.
There are many thousands of different Types of Resistor and are produced in a variety of forms because their particular characteristics and accuracy suit certain areas of application, such as High Stability, High Voltage, High Current etc, or are used as general purpose resistors where their characteristics are less of a problem.
Some of the common characteristics associated with the humble resistor are; Temperature Coefficient, Voltage Coefficient, Noise, Frequency Response, Power as well as a resistors Temperature Rating, Physical Size and Reliability.
In all Electrical and Electronic circuit diagrams and schematics, the most commonly used symbol for a fixed value resistor is that of a “zig-zag” type line with the value of its resistance given in Ohms, Ω. Resistors have fixed resistance values from less than one ohm, ( <1Ω ) to well over tens of millions of ohms, ( >10MΩ ) in value.
Types of Resistor
· Carbon Composition Resistor – Made of carbon dust or graphite paste, low wattage values
· Film or Cermet Resistor – Made from conductive metal oxide paste, very low wattage values
· Wire-wound Resistor – Metallic bodies for heatsink mounting, very high wattage ratings
· Semiconductor Resistor – High frequency/precision surface mount thin film technology
