Inductor / Coil Symbol
Definition: The Inductor (Coil) symbol represents a passive component that stores energy in a magnetic field — drawn as a series of arched loops or humps (ANSI Y32.2 / IEEE 315) or as a filled rectangle (IEC 60617) — that opposes changes in current through electromagnetic induction, with inductance measured in henries (H, mH, or µH); inductors are designated L in schematics, as defined in IEC 60617-04 and ANSI Y32.2 / IEEE 315, and have two terminals labelled A and B.
Also known as: inductor symbol, coil symbol, choke symbol, inductor coil symbol, L symbol schematic, solenoid coil symbol, reactor symbol, inductor schematic symbol.
What the Inductor / Coil symbol means
The Inductor / Coil symbol in a circuit diagram marks a component that stores energy in a magnetic field proportional to the current flowing through it. When current through the inductor changes, the inductor generates a back-EMF (electromotive force) opposing that change — a property described by Faraday's law of induction (V = L × dI/dt). This behaviour makes inductors fundamental in filtering, energy storage, and resonant circuits. The symbol's series of loops or humps visually represents the physical wire coils wound around a former or core that constitute the component.
Inductor symbols may be modified to indicate the core material: the basic looped symbol with no core lines indicates an air-core inductor; two parallel lines above (IEC) or to the side of the loops indicate a ferromagnetic (iron or ferrite) core; a dashed line indicates a powdered-iron or ferrite core with specific permeability. A variable inductor symbol adds an arrow through the coil loops. When two inductors share a magnetic core — as in a transformer or a coupled choke — the symbols are drawn side by side with coupling lines or dots indicating polarity, and may be annotated with a mutual inductance value M.
How to identify the Inductor / Coil symbol
In the ANSI Y32.2 / IEEE 315 convention, the inductor symbol is drawn as a row of three to six arched loops (humps) in series along the signal line, each hump representing one turn of the winding. The overall shape resembles a series of connected semi-circles sitting above the horizontal conductor line, with terminal A at the left end and terminal B at the right end. In IEC 60617 (symbol group 04, passive components), the inductor is drawn as a plain filled rectangle, similar in outline to the IEC resistor symbol — the distinction being context (the designator L vs R) and, where shown, adjacent core lines. No internal division marks appear in either symbol for a simple air-core inductor.
Function in a circuit
An inductor opposes changes in the current flowing through it by storing energy in its surrounding magnetic field when current increases, and releasing that energy back into the circuit when current decreases. At DC steady-state, an ideal inductor acts as a short circuit (only its winding resistance limits current). At AC frequencies, an inductor's opposition to current — its inductive reactance XL = 2πfL (ohms) — increases linearly with frequency, making it a high-frequency blocker and low-frequency pass-through element. This frequency-selective behaviour is exploited in LC filters, power-factor correction circuits, energy-storage inductors in DC-DC converters, and RF chokes blocking high-frequency interference from DC supply lines.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-04 (passive components) defines the inductor symbol as a rectangle with terminal lines at each end (identical in outline to the IEC resistor rectangle). Core modifications — two lines above the rectangle for iron core, a dashed line for ferrite — are specified in the same section. The designator letter is L and inductance is expressed in henries (H), as defined in IEC 80000-6. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 (R1989) / IEEE 315-1975, section 3.6, defines the inductor symbol as a series of arched loops (humps) along the conductor line. The number of humps (typically three to four) is not strictly prescribed. Core lines are shown above or below the loops for iron-core inductors. The designator is L. |
| Key difference | The IEC 60617 inductor symbol is a plain rectangle — visually identical to the IEC resistor; the component type is distinguished solely by the designator (L vs R) and context. The ANSI Y32.2 inductor symbol is the well-known series of arched loops/humps, making it instantly visually distinct from any other ANSI symbol. This is the most significant IEC vs ANSI difference for inductors: a rectangle (IEC) versus humps (ANSI). |
Terminals / pins
| Pin | Name |
|---|---|
| a | A |
| b | B |
Typical values
Inductance range: 1 nH (RF chip inductors) to several henries (mains filter chokes). Common ranges by application: RF circuits 1 nH–1 µH; switched-mode power supply output chokes 1 µH–2.2 mH; mains power-factor correction 1 mH–100 mH; audio crossover chokes 0.1 mH–10 mH. Current rating: 10 mA–100 A depending on size and core. DC resistance (DCR): 1 mΩ–50 Ω. Tolerance: ±5%, ±10%, ±20%.
Where the Inductor / Coil symbol is used
- Switch-mode power supply (SMPS) output filters — 10 µH–470 µH choke in the LC output filter of a buck, boost, or buck-boost converter to smooth the switched current waveform
- EMI/RFI suppression — common-mode and differential-mode chokes on power supply input lines to block high-frequency interference from reaching mains wiring
- LC resonant circuits — inductor paired with a capacitor in series or parallel to form a bandpass, band-reject, or tuned RF filter
- RF circuits — small air-core inductors (1 nH–100 nH) used in impedance-matching networks, VCO tank circuits, and antenna matching on PCBs
- Power-factor correction (PFC) — large boost inductors (100 µH–2 mH) in active PFC front-end stages of AC-DC converters
- Audio crossover networks — series inductors in passive loudspeaker crossover low-pass filters blocking treble frequencies from woofers
- Energy storage inductors in inductive charging — Qi wireless charging transmitter coils and receiver coils shown as air-core inductors with coupling annotation
Example
In a 5 V buck converter schematic, an inductor symbol labelled L1 (value 22 µH) is placed in series between the switching node of a PWM controller IC and the output capacitor C1; the inductor symbol's terminal A connects to the switch node pin of the IC and terminal B feeds the output rail, illustrating how the inductor symbol represents the energy-storage element that smooths the pulsed switch output into a steady DC voltage.
Key facts
- The Inductor / Coil symbol is designated L in both IEC 60617 and ANSI Y32.2 / IEEE 315; inductance is measured in henries (H), millihenries (mH), or microhenries (µH) per SI unit IEC 80000-6.
- The inductor symbol has two terminals: A (input/first terminal) and B (output/second terminal); inductors are non-polar components — current may flow in either direction.
- IEC 60617-04 draws the inductor as a plain rectangle (identical in outline to the IEC resistor); ANSI Y32.2 draws it as a series of arched loops (humps) — this is the most visually prominent IEC vs ANSI difference for inductors.
- Core lines modify the inductor symbol: two solid lines alongside the loops or rectangle indicate a ferromagnetic core; a dashed line indicates a ferrite or powdered-iron core; no lines means an air core.
- Inductive reactance XL = 2πfL (ohms) increases with frequency, making an inductor a natural high-frequency blocker and DC pass-through element.
- A variable inductor symbol adds a diagonal arrow through the coil loops (ANSI) or an arrow through the rectangle (IEC) to indicate an adjustable inductance.
- Coupled inductors (mutual inductance) are shown as two inductor symbols side by side with coupling dots and annotated with mutual inductance M; this notation is also used for transformer coils in schematic capture tools.
- Common inductor designator prefixes: L for general inductors, FL for filter inductors, T for coupled inductors used as transformers.
Diagrams that use this symbol
- tube light diagram
- fluorescent light wiring diagram
- led tube light connection diagram
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- tube light circuit diagram
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- fluorescent lamp circuit diagram
- tube light connection diagram
Frequently asked questions
What does the inductor symbol look like?
In ANSI Y32.2 / IEEE 315 schematics, the inductor symbol is drawn as a series of three to six arched loops (humps) sitting along a horizontal line, with a terminal at each end. In IEC 60617 schematics, the inductor is drawn as a plain rectangle with terminals at each end — visually similar to the IEC resistor symbol, distinguished by the L designator and any adjacent core lines.
What does the inductor symbol mean in a circuit diagram?
The inductor symbol means an energy-storing coil is present at that point. The inductor stores energy in a magnetic field when current flows and opposes any change in that current. In practice, it acts as a low-pass filter element (passes DC and low frequencies, blocks high frequencies) and is used to smooth current ripple, block RF interference, or form resonant LC circuits.
What is the designator letter for an inductor?
The standard designator letter for an inductor is L, per both IEC 60617 and ANSI Y32.2 / IEEE 315. Individual inductors are labelled L1, L2, etc. in schematics. The inductance value in henries (H), millihenries (mH), or microhenries (µH) is written alongside the L designator.
What is the difference between the IEC and ANSI inductor symbol?
The IEC 60617 inductor symbol is a plain rectangle (identical in shape to the IEC resistor rectangle). The ANSI Y32.2 / IEEE 315 inductor symbol is a series of arched loops or humps along the conductor line. This is the most significant visual difference between the two standards for this component. Both use the designator L and express inductance in henries.
What do the lines above or beside the inductor symbol mean?
Lines alongside the inductor symbol indicate the core material. Two solid parallel lines (IEC: above the rectangle; ANSI: above the humps) indicate a ferromagnetic iron core. A single dashed line indicates a ferrite or powdered-iron core. No additional lines means an air-core inductor. Core material determines the inductance value, saturation current, and frequency range of the component.
What is the unit of inductance and what values are typical?
Inductance is measured in henries (H), with practical values for most circuits expressed as millihenries (mH, 10⁻³ H) or microhenries (µH, 10⁻⁶ H). RF chip inductors range from 1 nH to 1 µH; SMPS output chokes range from 1 µH to 2.2 mH; mains filter chokes range from 1 mH to 100 mH. The value and tolerance (e.g. 22 µH ±10%) are written beside the L designator on the schematic.
Is an inductor a polarised component?
No — a standard inductor is a non-polarised component. Current may flow through it in either direction without damage, and the symbol has no polarity markings. The exception is coupled inductors and transformers, where polarity dots are added to indicate the phase relationship between windings.
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