Resistors and types of resistors

Resistors and types of resistors
Resistors and types of resistors

In this article, we are going to learn about electrical resistors, types, and their applications, both at an industrial and commercial level. Resistors, also technically called resistors, are devices that offer certain opposition to the passage of current and voltage. They are used to regulate the current and voltage in a certain circuit.

Resistors are the most common electronic component. They are a critical piece in almost every circuit and play a very important role in our favorite equation, Ohm’s Law.

The symbol for resistance is the ohm, which is represented by the Greek letter omega (Ω).

The resistance uses sub-multiples such as:

  • kilo-ohmio(1K Ω)=1000Ω.
  • Mega-ohmio(1MΩ)=1 000 000Ω.

Note: They are only manufactured up to mega-ohm, there are no resistors with values ​​higher than this.

If we want to regulate the current we must place it in series and if, on the other hand, we want to regulate the voltage we would have to place it in parallel with the device we want to protect.

The main function of resistors is to protect devices that cannot withstand certain voltages or currents produced by the power supply.

Types of resistors

A) Resistors of fixed values.

  1. Carbon or film resistance.
  2. Fuse alloy resistance.
  3. Wound or wire resistors.
electrical resistors types and applications
Fixed value resistors

B) Resistors of variable values.

  1. Varistor/s.
  2. Thermistor or thermistors.
  3. Potentiometer or rheostat.
Resistors of variable values

Carbon or film resistance

This resistance uses a color code to be able to be interpreted, internally they are composed of a very thin film wrapped in a reel or a carbonaceous or graphite material, which depending on its purities to that same extent will carry out the opposition.

Carbon or film resistance
Carbon or film resistance

Resistance Alloy Fuse

This type of resistance is made of a fluxing material, which turns into ashes under sudden changes in temperature. Unlike the previous resistance, it has its value printed on its body. Fusible alloy resistors are always installed at the input of a signal, to protect a circuit.

Alloy Fuse Resistance

Wound or wire resistors

It is the resistor that has the greatest power capacity in electrical and electronic circuits. It usually works against alternating current, since its power is from 0.5 to 27 volts, depending on the capacity of the circuit.Its body is made of ceramic and like the fuse alloy, it also has its values ​​printed on its body.

Resistance windings or wire


It is a two-terminal resistor with infinite ohmic value, which under sudden changes in voltage and current, at a given moment can conduct in both directions. This occurs when the winding voltage (maximum) exceeds the infinite level of the varistor capacity.

It works combined with the alternating protection fuse. The fuse protects from sudden changes in current and the varistor from voltage changes.

Note: The varistor returns the excess voltage back and a node is formed, increasing the voltage and blowing the fuse.

If the equipment supports 120 volts and the voltage rises to 180 volts, the varistor returns 60 volts, this voltage is added to the 180 volts, resulting in 240 volts.

When a node is formed, the varistor remains in a short circuit, therefore for the equipment to turn on, one terminal of the varistor must be lifted, just to test, then it must be replaced.

Thermistor or thermistors

This device has a physical structure similar to the varistor, it differs from it in that it produces variations with respect to the current, because it is installed in series with respect to the load. There are two categories regarding this resistance:

A) The negative temperature coefficient (NTC): Works for cold areas or cooling currents.

B) Positive temperature coefficient, works for hot or positive areas (NTC).


Potentiometer or rheostat

It is a three-terminal mechanical resistor that varies both voltage and current.

It makes voltage variations when it works as a potentiometer and current variations when it works as a rheostat.

Basic Resistors

Resistors are electronic components that have a specific electrical resistivity that never changes. The resistivity of the resistor  limits the flow of electrons  in a circuit.

Resistors are  passive components,  which means that they only consume energy (and cannot generate it). Resistors are generally added to circuits as a complement to  active components such  as operational amplifiers, microcontrollers, and other integrated circuits. and Resistors are generally used to limit current, divide voltages, and as pull-up resistors on the input and output (I/O) lines.

Resistance Units

Electrical resistance is measured in  ohms. The symbol for ohm is the uppercase Greek letter omega: Ω. The definition of 1 Ω is the resistance between two points where 1 volt (1V) of applied potential energy can push 1 ampere (1A) of current.

Larger or smaller values ​​can be used with prefixes such as kilo-, mega-, or giga-, for example, to make them easier to interpret. It is very common to find resistances in the order of kilo ohm (kΩ) and mega ohm (MΩ). It is less common to see resistances in the milli ohm (mΩ) range. For example, a 4,700 Ω resistor is equivalent to a 4.7 kΩ resistor. A 5,600,000Ω resistor can be written as 5,600kΩ or more commonly as 5.6MΩ.

Schematic Symbol

All resistors have  two terminals,  one connection at each end of the resistor. When modeled on a schematic, a resistor will appear as one of two symbols:

Two common schematic symbols for resistors.  R1 is a 1kΩ resistor in the American style, and R2 is a 47kΩ resistor in the international style
Two common schematic symbols for resistors. R1 is a 1kΩ resistor in the American style, and R2 is a 47kΩ resistor in the international style.


The terminals of the resistors are each of the lines that extend from the zigzag (or rectangle). That’s what connects the resistor to the rest of the circuit.

Resistor symbols usually carry a resistance value and a name. The value displayed in ohms is obviously critical for both evaluation and circuit construction. The name of the resistor is usually   followed by a number. Each resistor in a circuit should have a unique name/number. For example, below are some resistors needed to run a 555 timer circuit:

In this circuit, resistors play a key role in setting the frequency of the 555 timer output. Another resistor (R3) limits the amount of current that passes through the LED.

In this circuit, resistors play a key role in setting the frequency of the output of the 555 timer. The resistor (R3) limits the amount of current that passes through the LED.

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