What Is an Inductor (Coil)?
An inductor (coil) is a passive component that stores energy in the magnetic field created by the current through it and resists sudden changes in that current. Along with the resistor and capacitor, it's one of the three basic passive elements.
How Does It Work?
When current flows through a coil formed by winding a conductor, a magnetic field arises around it. When the current tries to change, the coil produces a voltage that opposes the change and resists it; that is, it "smooths" the current. This property is called inductance, and its unit is the henry (H).
What Does Inductance Depend On?
The number of turns, the coil's area and the core material set the inductance. A ferrite or iron core concentrates the magnetic field, giving much higher inductance in the same size.
| Property | Behavior |
|---|---|
| At DC | Low resistance (like a short) |
| At AC | Resistance rising with frequency (reactance) |
| Energy | Stored in the magnetic field |
Difference From a Capacitor
A capacitor stores energy in the electric field (as voltage) and resists voltage changes; an inductor stores energy in the magnetic field (as current) and resists current changes. The two form resonance together in LC circuits.
Where Is It Used?
DC-DC converters, power filters, RF circuits, EMI suppression and audio pass/block filters. For high-current switching power circuits a dedicated power inductor is used.
Common Mistakes
- Ignoring saturation: when the core saturates the inductance collapses; the current rises uncontrollably.
- Overlooking DCR: the winding wire's resistance produces loss and heat.
- Current rating: an inductor beyond its rated current heats up and performance drops.
Frequently Asked Questions
What is the unit of inductance?+
Why does a coil pass DC but block AC?+
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