Active vs. Passive Electronic Components: Understanding Their Roles

Passive Devices

Passive devices are components that cannot modulate current using an external electrical signal. Classic examples include resistors, capacitors, inductors, transformers, and even diodes.

Active Devices

An active device can electrically control the flow of charge—essentially, it lets electricity control other electricity. For a circuit to be truly electronic, it must contain at least one active component. Typical examples are vacuum tubes, transistors, silicon‑controlled rectifiers (SCRs), and TRIACs.

Although a saturable reactor can modulate AC current with DC, it is rarely categorized as active. Detailed discussions of each active device’s operation appear in later chapters.

Functions of Active Devices

All active devices regulate electric charge flow. Some use a voltage to control the current (voltage‑controlled devices), while others use one current to control another (current‑controlled devices).

For instance, vacuum tubes are voltage‑controlled, whereas transistors can be either voltage‑controlled or current‑controlled. The first transistor demonstrated was a current‑controlled device.

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