discrete component
a component with just one circuit element, either passive (resistor, capacitor, inductor) or active (transistor or vacuum tube).
discrete component: one function, one package, one wire
A discrete component is a single electrical element packaged and sold as a standalone unit. It performs one specific function: a resistor limits current; a capacitor stores charge; a transistor amplifies or switches; a diode conducts in one direction. Unlike integrated circuits, which contain thousands or millions of elements etched onto silicon, a discrete component does one job in one package.
Discrete passives dominate industrial electronics. A carbon film resistor is just a thin film of carbon deposited on a ceramic tube, with leads soldered to each end. Film capacitors use plastic film as the dielectric, rolled tightly with metal electrodes. Inductors are wire wound on a ferrite or iron core. These components are measured by their primary parameter: resistors in ohms, capacitors in farads, inductors in henries. Tolerances matter. A 10 kilohm resistor might be rated at plus or minus 5 percent or plus or minus 1 percent, and the tighter tolerance costs more and delivers accuracy where circuits demand it.
Active discretes, mainly semiconductors, include signal transistors (small-signal BJTs and MOSFETs for amplification and logic), power transistors (for heavier loads), and diodes (rectifiers, Zener diodes for voltage regulation, photodiodes for sensing). A 2N3904 NPN transistor or an IRF520N MOSFET are staples in industrial control and power supplies. Each semiconductor device has a datasheet specifying gain, voltage ratings, current handling, and switching speed.
Why discrete components still matter: integrated circuits are cheaper and smaller at high volume, but discrete components offer flexibility, repairability, and thermal management that ICs cannot match. A failed resistor in a large industrial cabinet can be unsoldered and replaced in minutes. Discrete power transistors can be bolted to heatsinks rated for hundreds of watts. Designers also use discretes to tune performance: swap a 100 microfarad capacitor for a 47 microfarad one and change the circuit's response in seconds.
The term "discrete" means separate or distinct, emphasizing that each component is a separate, replaceable unit. This contrasts with integrated circuits where components are fabricated together and cannot be separated. In PCB assembly, discrete components are still hand-placed or machine-placed individually, even in modern factories, whereas ICs come as prefabricated modules. Sourcing remains fragmented: thousands of suppliers stock commodity resistors and capacitors, but specialized discretes like high-voltage diodes or precision inductors demand relationships with specialists.