Power inductorFerrite beadTransformer isolationwiki/embedded-inductor-types
TL;DR
An inductor wraps a coil around a high-permeability core; its identity is back-EMF that opposes any change in current (Lenz's law) — the current-side dual of a capacitor. Three uses: a power inductor that stores energy (DC-DC buck/boost), a ferrite bead that acts resistive at high frequency to burn noise as I²R heat, and a motor modeled as R+L+back-EMF. A transformer's core value is electrical isolation, since the windings couple only through magnetic flux.
What an inductor is — inertia of current
A passive part: a coil on a magnetic core. When current changes, it generates back-EMF v = L·di/dt opposing the change (Lenz's law).
More turns → larger L; it stores energy as E=½Li² — the current-side dual of the capacitor's E=½CV².
Three uses + impedance
Power inductor — can/toroidal shapes storing energy in DC-DC buck/boost supplies, up to tens of amps. Toroidals trap flux in the core, cutting leakage and EMI.
Ferrite bead — a broad resistive region at high frequency that absorbs noise current as I²R heat (absorbing, not reflecting).
Mirror of the capacitor — past self-resonance (SRF) each flips to its opposite: the inductor turns capacitive, the capacitor inductive.
🧲Inductor
🔋Power inductorStores energy ½Li²
🧹Ferrite beadNoise → I²R heat
⚙Motor modelR + L + back-EMF
One inductor, three uses
Transformer — the real value is isolation
Primary and secondary share a core but aren't physically connected — coupled only by flux. Voltage follows the turns ratio (V1/V2 = N1/N2).
The key is electrical isolation — you only contact the safe secondary (12 V), never the 400 V directly. It's how a phone charger's flyback converter steps 220 V AC down to DC while staying isolated.
Primary N1AC in
🧲CoreFlux path
Secondary N2V2 = V1·N2/N1
Coupled only by flux — electrical isolation
Kickboard board context
The buck converter's power inductor stores energy while stepping down, and ferrite beads on signal/power lines soak up high-frequency noise as heat.
Pitfalls & gotchas
Two gaps the lecture deferred — the motor equivalent circuit (R+L+back-EMF) comes in the motor-control course, and saturation current / DCR (the inductor-selection trap) stays to be filled. The raw transcript has many STT errors, so check the correction table at its top first.