Inductor / Coil
Inductor
A passive component that stores energy in a magnetic field when current flows through it, opposing changes in current flow. Used for filtering, tuning, and energy storage.
Schematic symbol
Inductor / coil
How inductor / coil appears in a circuit diagram.
Types & variants
Key specs
Inductance
Henry (H)Amount of energy stored per ampere of current. Common subunits: mH, µH, nH.
Current rating
Ampere (A)Max current before inductor saturates or overheats.
DC resistance
Ohm (Ω)Resistance of the wire winding. Lower is better for power applications.
Self-resonant frequency
Hertz (Hz)Frequency where inductance stops working (acts like a capacitor).
Q factor
UnitlessQuality factor - higher means less energy loss (better efficiency).
Markings
Through-hole: Often printed value with unit (e.g., 100µH). SMD: 3-digit code (e.g., 101 = 10 x 10^1 = 100nH), sometimes with 'nH' or 'µH' suffix.
Standard values
Common: 1µH, 10µH, 100µH, 1mH, 10mH. RF values: 10nH, 100nH, 1µH. Values often follow E12/E24 series.
How to choose
1) Determine required inductance for your circuit (depends on frequency and application). 2) Check current rating exceeds your circuit's max current. 3) Consider DC resistance for power efficiency. 4) Select appropriate core material for your frequency range.
Pinout & package
2 leads (non-polar, can go either way). Packages: Radial/axial (through-hole), drum/epoxy (shielded), 0402/0603/0805/1206 (SMD), toroidal rings.
Example circuits
- LC filter (low-pass, high-pass, band-pass)
- Buck/boost converter
- Oscillator tank circuit
- RF matching network
- EMI/RFI suppression
Common failures
Open circuit (burnt wire), shorted turns, increased DC resistance, core cracking. Physical signs: burnt smell, discoloration, cracks in core or epoxy.
How to test
Use LCR meter for accurate inductance measurement. With multimeter: Check for continuity (should show low resistance, not open). Cannot measure inductance with standard multimeter.
Substitutes
Use nearest standard inductance value. For RF, must match SRF. Can combine inductors in series/parallel for custom values (series: L1+L2, parallel: 1/(1/L1+1/L2)).