Magnetics in Practice (Inductors & Transformers Beyond the Ideal)#

The Passive Components section covers what inductors and transformers are and how they behave in theory. This section covers how they actually behave on the bench — the non-ideal effects that cause circuits to overheat, ring, buzz, saturate, or fail at startup.

Real magnetic components are lossy, nonlinear, and frequency-dependent. Their behavior changes with current level, temperature, and drive waveform in ways that resistors and (most) capacitors don’t. If a switching power supply doesn’t work, or a transformer runs hot, or an inductor screams on the bench, the answer is usually in this section.

What This Section Covers#

• Saturation in Practice — What happens when a core runs out of magnetic headroom, why it depends on current and temperature, and how to see it on the scope.
• Winding and Core Losses — DCR, copper loss, hysteresis, eddy currents, and why an inductor gets hot even when “nothing is wrong.”
• Leakage, Stray Capacitance & Ringing — The parasitics that turn clean switching waveforms into ringing messes, and where they come from.
• Audible Noise: Whine, Hum & Buzz — Magnetostriction, loose windings, and why power supplies and transformers make audible noise.
• Inrush Current & Startup Stress — Why magnetics create current spikes at power-on that blow fuses, trip breakers, and stress components.
• Selecting Magnetics by Application — What specs matter for a buck converter inductor vs. an audio transformer vs. an isolation barrier — and how to read a magnetics datasheet without drowning.

For diagnosing magnetics problems at the bench — scope waveforms, thermal signatures, LCR meter checks, and current-draw patterns — see Diagnosing Magnetics on the Bench in the Debugging section.