Inductors without the mystery.

If a capacitor resists sudden voltage change, an inductor resists sudden current change. Push current through a coil and it builds a magnetic field. Change the current and the changing magnetic field creates a voltage that opposes that change.

Inductance and current

Inductance is measured in henries, though practical electronics often uses microhenries and millihenries. A switching regulator might use 1 uH to 47 uH. A filter or choke may use a larger value. The value tells you how strongly the inductor resists current change.

Current rating matters as much as inductance. Inductors are often wound around magnetic cores. If the core saturates, the inductor can lose much of its useful inductance. In a power supply this can cause high ripple, overheating, poor regulation, or failure.

DCR and heating

The wire inside an inductor has resistance, usually listed as DCR or DC resistance. Current through that resistance creates heat. A low DCR inductor is usually better for efficient power conversion, but it may be physically larger or more expensive.

The simple power estimate is the same as for a resistor:

P = I^2 x DCR

This is not the whole loss story at high frequency, but it is a good first sanity check.

Switching regulators

Buck, boost, and buck-boost regulators use inductors to transfer energy efficiently. The controller switches current through the inductor rapidly. The inductor smooths that pulsed energy into a more controlled current path.

This is why regulator datasheets usually provide recommended inductor values, saturation current, RMS current, DCR, and sometimes part numbers. Substituting "anything close" can work in a forgiving design, but it can also create noise, heat, or instability.

Flyback from coils

Relays, solenoids, motors, and speakers all have inductive behaviour. When current through a coil is interrupted, the inductor tries to keep current flowing. If there is no safe path, the voltage can rise high enough to damage a transistor, microcontroller, or switch contact.

A flyback diode across a DC relay coil gives that current a path when the switch turns off. Other circuits may use TVS diodes, snubbers, or clamp networks depending on speed and energy.

Filters and EMI

Inductors oppose changing current, so they can help block high frequency noise while allowing DC or low-frequency current through. Ferrite beads, common-mode chokes, and LC filters are common in power inputs, USB lines, motor drives, radio circuits, and noisy digital boards.

Filters are layout-sensitive. A perfect-looking schematic can perform badly if the PCB routes noisy current through the wrong loop or places the filter so that noise couples around it.

Parameter	Why it matters
Inductance	Sets energy storage and current ripple behaviour.
Saturation current	Current where the part stops behaving like the chosen value.
RMS current	Thermal current rating for continuous operation.
DCR	Winding resistance, efficiency, and heating.
Shielding	How much magnetic field leaks into nearby circuitry.

Common mistakes

• Checking inductance but ignoring saturation current.
• Ignoring DCR and then wondering why the part gets warm.
• Replacing a regulator inductor without checking the datasheet recommendations.
• Driving a relay or motor without a suitable flyback or clamp path.
• Putting noise filters in the schematic but placing them poorly on the PCB.

A practical checklist

1. What current will flow through the inductor in normal and fault conditions?
2. Is the saturation current comfortably above the peak current?
3. Is RMS current and DCR acceptable for heating and efficiency?
4. Does the part need shielding to protect nearby signals?
5. Is the PCB layout suitable for the switching or noise current loops?
6. Is there a safe path for stored energy when switching a coil off?