Inductor / coil (100 µH) · Exterior view
Epoxy coating and color bands · brown-black-brown = 100 µHSilver band (10%)Pins
Axial body with color rings or a printed value and two pins
Body ≈ 8–12 × 3–5 mm; two axial pins (depends on the series)
Inductors and transformers

Inductor / coil (100 µH)

In simple terms
What is this?

The heavy flywheel of electricity. When current wants to change suddenly it resists; a heavy wheel also delays speeding up and stopping.

What is it for?

Slows sudden changes in current; smooths ripple in filter and power circuits.

Where do you see it?

Small cylinders made of wound wire, inside computers and chargers.

How do you spot it?

A small cylinder that looks like a resistor; it has thin wound wire inside, and two pins come out of the ends.

Caution:

If you cut the current suddenly, a spark or high-voltage spike appears; with current above the limit it cannot do its job.

Technical definition

A passive component made by winding insulated copper wire around a core. It stores energy in a magnetic field and produces a voltage that opposes sudden changes in the current through it. In steady DC an ideal inductor behaves like a short circuit; a real inductor has the DC resistance of its wire.

Inductance100 µH
Tolerance±10% · ±20%
DC resistance≈0.3–1 Ω
Schematic symbol IEC and ANSI differ

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 2
1Winding end aNon-polarized, can be connected in the series linea
2Winding end bThe other end of the same windingb
Features typical
Inductance
100 µH
Tolerance
±10% or ±20%
DC resistance (DCR)
≈0.3–1 Ω (example axial series)
Saturation current (Isat)
In series; the current at which inductance drops by the stated ratio
Heating current (Irms)
Limited by the allowed temperature rise
Energy
E = ½ × L × I²
High frequency
Above its self-resonant frequency it does not behave like an inductor
Example part
100 µH axial ferrite inductor
Common mistakes
Confusing inductance with resistanceThe multimeter’s Ω mode shows the wire’s DCR, not the 100 µH.
Exceeding IsatWhen the core saturates, the inductance drops. Check both the Isat and the heating-current limits in the datasheet.
Cutting the current suddenlyThe coil produces a high-voltage spike. In a switched circuit use a freewheeling path rated for the current.

Test with a multimeter

Test whether this part is good with the multimeter on the measurement screen.

Take a measurement
Where it is used
LC filterSwitching power stageExamining how the current changes
Related lessons
Filtering the power supply
Module 3 · Capacitor and timesoonDriving a relay and the flyback diode
Module 4 · Diode and transistorsoonMeasuring resistance and continuity
Module 2 · Measuring with a multimetersoon
Try it in the Lab