An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components have two or more electrical terminals (or leads), usually connecting to a printed circuit board, to create an electronic circuit. They may be packaged as arrays or networks of like components, or integrated inside of packages such as semiconductor integrated circuits, hybrid integrated circuits, or thick film devices.
A component may be classified as passive, active, or electromechanical. The strict physics definition treats passive components as ones that cannot supply energy themselves, whereas active component act as a source of energy. However, electronic engineers who perform circuit analysis use a more restrictive definition of passivity, (see Wikipedia:Incremental passivity). When only concerned with the energy of electronic signals, it is convenient to ignore the DC circuit and pretend that the power supplying components such as transistors or integrated circuits is absent (as if each such component had its own battery built in). Then, the analysis only concerns the AC circuit. This for instance, lets us view an oscillator as "producing energy" even though in reality the oscillator consumes even more energy from a DC power supply. Under that restriction, the terms as used in circuit analysis are defined as:
- Active components
- Rely on a source of energy and usually can inject power into a circuit. Active components include amplifying components such as transistors, triode vacuum tubes (valves), and tunnel diodes.
- Passive components
- Can't introduce net energy into the circuit. They also can't rely on a source of power, except for what is available from the circuit they are connected to. As a consequence they can't amplify (increase the power of a signal), although they may increase a voltage or current (such as is done by a transformer or resonant circuit). Passive components include two-terminal components such as resistors, capacitors, inductors, and transformers.
- Electromechanical components
- Can carry out electrical operations by using moving parts or by using electrical connections.
Most passive components with more than two terminals can be described in terms of two-port parameters that satisfy the principle of reciprocity, although there are rare exceptions. In contrast, active components (with more than two terminals) generally lack that property..