Passive Electronic Components 101: How They Work and Their Role in Circuits

Passive electronic components are essential in electrical circuitry. They are not only an integral part of a circuit’s physical structure, but they also help illuminate how electricity works in complex electrical systems. Printed circuit boards (PCBs) and integrated circuits often contain these components that operate on their own – or discretely – within these devices. These are then used to convert and stabilize power, filter electrical current and configure integrated circuits. Since all circuit boards contain a certain amount of passive electronic components, designers of modern PCBs need to understand how these components will interact with electrical current.

Basics of Passive Electronic Components

Passive electronic parts do not control the current coming from external sources. They neither augment nor amplify electrical signals. 

All passive electronic components have these two properties:  

  1. They do not generate electrical power, but rather dissipate or store it. 
  2. They function without a power source, influencing the flow of power so that electrical output cannot be adjusted externally. 

Modern electronics categorizes electronics as either active or passive, and circuits as either linear or nonlinear in their response. 

Active & Passive Electronic Components 

Unlike passive electronic components, active ones require power to work. These active devices include integrated circuits, transistors and amplifiers. Additionally, the way in which components respond to electrical current – in a linear or nonlinear manner – distinguishes their relationship to electrical signals. When graphing output and input signals, a straight-lined graph represents input signal levels for linear circuits, whereas output graphed for nonlinear circuits presents itself as a curved line when graphed. 

Passive electronic components can, however, respond in either a linear or nonlinear fashion. Diodes, for example, use nonlinear current when voltage drops across it. Yet diodes are passive, as they require no power source. However, though active electronic components tend to be nonlinear, not all nonlinear components can be active, as some nonlinear circuits are also passive. 

These active components either generate power themselves or require power sources in order to operate. The change in the level of power then alters the output coming from active components. Transistors are perhaps the most commonly used active electronic components, which require a certain amount of current to turn on these devices. 

Types of Passive Electronic Components

The most common types of passive components are resistors, capacitors and coil inductors. 

In brief, the three main components that make up a circuit work as follows: 

  • Capacitors are made from two conductive plates, separated by insulating material, that continually stores and releases electrical charges, allowing alternating current (AC) to pass through it while blocking direct current (DC). Using an electrical field, capacitors control current fluctuations within circuits to keep a signal from becoming distorted. 
  • Inductors – also known as coils – use wiring coiled into a loop that forms around its core, which produces a magnetic field that temporarily stores electricity and restricts the flow of AC as DC passes through them. This stored energy returns to the circuit, which helps filter out unwanted frequencies and reduces current spiking. 
  • Resistors feature two interchangeable leads that restrict current flow, precisely controlling the amount of current flowing through circuits while also managing voltage. Within circuits, resistors often have specialized functions; for example, a termination resistor prevents a pulse signal along a transmission line from reflecting back, so it will not interfere with the next pulse. 

Other passive components include:  

  • Antennas
  • Assembly modules
  • Cables
  • Circuit protection devices
  • Crystals
  • Detectors
  • Diodes
  • Memristors 
  • PCBs (Printed circuit boards)
  • Piezoelectric devices
  • Resonators
  • Sensors
  • Switches
  • Terminals and connectors
  • Thermistors 
  • Transducers
  • Transducers
  • Transformers
  • Varactors 

These components are used to build various types of electronic circuits, with many and varied applications. Their functions within circuits include use as high-frequency filters, in power decoupling networks featuring multiple capacitors, for network termination or to match impedance between power sources convert electricity into another form of energy. PCB designers often use passive circuit elements when making sub-circuits and models that describe the behavior of electricity on the board. As such, they serve as both a physical component as well as tools that assist in creating ever more innovative PCBs. 

Using Passive Electronic Components in Circuits

Passive components are often used in electrical devices, either individually or in tandem. When connected within a circuit, they can work in parallel or in series, providing feedback or phase-shifting to the signal. However, since they cannot gain power, passive components are unable to multiply this signal. 

Being bi-directional, passive components connect either way within a circuit, unless their polarity is exact, as is the case with electrolytic capacitors. The predictable flow of electrical current from the positive to negative terminals determines the polarity of the voltage. 

Passive Components & PCB Manufacturing

As passive electronic components are incorporated into new PCB designs, finding accurate PCB footprints and understanding how to use them is imperative. Sometimes it makes sense to reuse existing footprints for newly designed boards, though these must be within appropriate tolerances to match the board’s land patterns. 

Fabricating PCBs involves a packaging technique in which certain components are attached to the circuit board via these through-holes. Modern computer chips are mostly surface-mounted, but passive components like capacitors and resistors are still mounted with through-holes. These allow the computer chips and discrete components to be attached with pins through the PCB. These are then soldered from below. This technique requires extra drilling and means losing a certain amount of space, though through-holed devices tend to have a stronger bond to the board. 

However, footprints for components that are either through-holed or surface-mounted must follow specific standards, which are time-consuming when done by hand. For this reason, finding the best PCB footprints for passive components with standard package sizes makes sense. This saves time that can then be better spent developing new electronic creations. 

To learn more about passive electronic components, please contact us at Solid State Inc. today!