Practical Electronics: Components and Techniques

Chapter 8. Passive Components

Passive components are the framework on which circuits are built. One way to think of a passive component is as something that only responds to voltage or current; it doesn’t exhibit any active control behavior. Stated more formally, a passive component either dissipates energy (resistors) or stores and releases energy (capacitors and inductors), but does not actively contribute energy.

Unlike transistors and integrated circuits, passive components don’t require a power supply, just whatever happens to be going through the circuit of which they are a part. In other words, a resistor simply resists, and a capacitor or inductor just responds to changes in voltage and frequency to store and release electrons in a consistently predictable way. There is no way, short of physical manipulation, to alter the intrinsic behavior of a passive device (as you’ll see, there are ways to physically manipulate a passive device and alter the behavior in a controlled way).

Something like a transistor, on the other hand, can be used with a control input to modify its response to voltage and current (i.e., it has gain), and active devices can exhibit nonlinear behaviors. An active device can also supply energy to a circuit via an external power source. For these reasons, transistors, and other semiconductor devices, are classified as active components (the subject of Chapter 9).

For an example of how important passive components are, a typical transistor circuit (perhaps ...