Resistors.

Resistors,
(resistors can look differently as well).


Definition.

A resistor is an electrical component that implements electrical resistance as a circuit element.

When choosing a resistor, four factors can be considered:
- value in Ohms (Ω),
- tolerance, for example: +/- 5%,
- power rate, maximum power which can be developed in a resistor without occuring damage by overheating,
- stability, ability to keep the same value with changes of temperature & with age.


Resistor Types.

- Fixed Resistors.

With fixed resistance & tolerance.

- Variable resistors.

Their resistance can be set, they also have tolerance - more or less precise.

- NTC Thermistors.

Negative Temperature Coefficient Resistors. Their resistance lowers with temperature's rise.

Usually their resistance is shown for temperature of 20 ^oC.

There are thermistors that are self-heated by an electric current's flow, so resistance depends also on electric current.

There are also thermistors through which small enough current is flowing, so the heat from the electricity is neglient & only outside heating counts as far as resistance is considered.

- PTC Thermistors.

Positive Temperature Coefficient Resistors. Their resistance rises with temperature's rise.

Most PTC thermistors are of the 'switching' type, which means that their resistance rises suddenly at a certain critical temperature.

- Varistors.

Also called VDR - Voltage Dependent Resistors.

Their resistance lowers strongly as Voltage rises.