Resistors

Electrical resistors are one of the most widely used passive electronic components in all types of circuits, from industrial applications and power systems to consumer electronic devices.

Their main function is to limit the flow of current and cause a voltage drop proportional to their ohmic value, thus regulating the circuit’s operation. An electrical resistor is designed to provide opposition to current flow and is key to protecting sensitive components, adjusting signals, dividing voltages, or controlling gain in electronic stages.

Types of Resistors

Depending on their construction, application, and behavior, there are different types of electronic resistors:

Resistencias fijas
Fixed ResistorsThey have a fixed ohmic value determined by the manufacturer that does not change. These are the most common in electronic circuits.
Variable Resistors
Allow manual adjustment of their resistance, such as potentiometers or trimmers.
Resistors Dependent on Physical Factors
Change their resistance based on temperature (NTC, PTC), light (LDR), or other parameters.

They can also be classified according to their mounting format:

Through-Hole Resistors (THT): feature leads that are inserted into the PCB and soldered on the underside. They are identified by a color code indicating their ohmic value, tolerance, and thermal coefficient.
SMD Resistors (Surface Mount Device): designed for surface mounting on high-density electronic boards. Their value is represented by a printed three- or four-digit numeric code.

How to read the value of an electrical resistor

The value of an electrical resistor can be determined in different ways, depending on the type:

• • In through-hole resistors, a color band code is used. Each color represents a number and is interpreted using a standard chart that defines the significant figures, multiplier, and tolerance.

• In SMD resistors, a printed numerical code is used. For example, the code “102” equals 1,000 ohms (10 × 10²). If “471” appears, it indicates 470 ohms (47 × 10¹).

The most common units are:

• • Ohms (Ω) for low values
• • Kilohms (kΩ) = 1,000 ohms
• • Megaohms (MΩ) = 1,000,000 ohms
  
  

Applications of electrical resistors

Resistors are present in virtually every electronic system. Some of their most common applications include:

• • Current limiting in LEDs and other devices
• • Voltage division in resistive networks
• • Passive filters in analog circuits
• • Gain control in amplifiers
• • Protection and adjustment of sensors
• • Test loads and simulation of operating conditions

Their reliability, low cost, and versatility make electronic resistors essential in sectors such as automotive, telecommunications, industrial control, medicine, home automation, and renewable energy.