For a circuit to be categorized as electronic, it should have at least one component that is an active device. Components that are not capable of controlling currents through another electrical signal are called passive devices. Passive devices include resistors, capacitors, transformers, inductors, and diodes. Active devices include transistors, vacuum tubes, silicon-controlled rectifiers and triacs, which are three-terminal semiconductor devices for directing currents.
When an electronic circuit is made entirely of passive components, it is referred to as a passive circuit. A battery, on the other hand, is an active component because it supplies energy.
The term passive might be somewhat ambiguous, depending on the field of study or engineering that you are involved in. Among analog designers, passive refers to systems that are incrementally passive. Among control system engineers, the term is used when referring to thermodynamically passive systems. You might need to get clarification to find out in what context a person is using the term passive.
If you don’t have much experience with engineering or electronics, the term could be misleading. The term passive is used when referring to circuit network theories and control systems. It refers to a component that uses energy but does not create energy on its own. Following this definition, any source of energy could be classified as active, but components such as resistors, capacitors, and diodes will be considered passive. A circuit designer might refer to the latter type of part as being thermodynamically passive.
A good general definition of passivity is a stable component whose properties are not subject to change. However, the same parts may not remain stable under every possible condition.
It is imperative to understand the difference between the active and passive parts of every electronic system. The difficulty lies in the fact that the definition will change a bit depending on who is describing the system. For help in understanding more about printed circuit board assembly components, talk to the professionals at EMS solutions.