Inductor Symbols
Circuit symbols provide a simple and standardised way of representing inductors in electronic schematics. Although different drawing standards such as IEC and ANSI may vary slightly in appearance, they all represent the same electrical component and function. Understanding these symbols is essential when reading, designing or repairing electronic circuits.
Standard Inductor Symbol
The basic inductor is represented by a series of curved loops that resemble a coil of wire.
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This symbol represents a general-purpose inductor where the core material is not specified.
Air-Core Inductor
Air-core inductors have no magnetic core and are commonly used in RF circuits because they have low core losses at high frequencies.
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Since there is no magnetic core, the standard coil symbol is sufficient.
Iron-Core Inductor
Iron-core inductors are represented by adding two parallel lines beside the coil to indicate the magnetic core.
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Iron-core inductors provide higher inductance than air-core designs and are commonly used in power and low-frequency applications.
Ferrite-Core Inductor
Ferrite-core inductors are often drawn using the same core symbol as other magnetic-core inductors.
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Ferrite materials are widely used in switch-mode power supplies and high-frequency filters.
Variable Inductor
A variable inductor includes an adjustable core or movable winding to change its inductance.
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↗
The diagonal arrow indicates that the inductance can be adjusted.
Tapped Inductor
Some inductors have one or more electrical taps along the winding.
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Tapped inductors are used for impedance matching, oscillators and tuned RF circuits.
Transformer Symbol
A transformer consists of two or more inductive windings that are magnetically coupled.
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Although transformers are separate components, their symbols are based on two inductors sharing a common magnetic core.
Common-Mode Choke
A common-mode choke contains two windings on a shared magnetic core.
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These devices are widely used for EMI suppression in power supplies and data communication equipment.
Symbol Comparison
| Symbol | Represents |
|---|---|
| )))))) | General or air-core inductor. |
| )))))) + core lines | Iron-core or ferrite-core inductor. |
| )))))) + arrow | Variable inductor. |
| )))●))) | Tapped inductor. |
| )))║║((( | Transformer or common-mode choke. |
Where These Symbols Are Used
- Electronic schematics.
- PCB design software.
- Service manuals.
- Circuit diagrams.
- Power supply documentation.
- Audio crossover designs.
- Radio-frequency circuit diagrams.
Reading Circuit Diagrams
Inductors are usually identified by the reference designator L, followed by a number.
| Reference | Example |
|---|---|
| L1 | Input filter inductor. |
| L2 | Power converter inductor. |
| L3 | Audio crossover inductor. |
| T1 | Transformer. |
| FL1 | Ferrite bead or EMI filter. |
Interesting Facts
- The letter L is used because the symbol I is already reserved for electric current.
- Most modern schematic software supports both IEC and ANSI inductor symbols.
- Core lines indicate a magnetic material but usually do not specify the exact core type.
- Transformers are represented by multiple inductive windings rather than a single coil.
Key Points
- The coil symbol represents an inductor.
- Core lines indicate a magnetic core.
- An arrow indicates an adjustable or variable inductor.
- Transformers and chokes use multiple coupled windings.
- Most inductors are identified by the reference letter L in circuit diagrams.