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Inductors & Ferrites

They resist changes in current. Two very different uses: power inductors store energy in switching regulators; ferrite beads suppress high-frequency noise.

Power inductors (switching regulators)​

  • The energy-storage element in a buck/boost. Value and current rating come from the regulator datasheet — follow it.
  • Key specs: inductance, saturation current (Isat) (don't exceed — inductance collapses), DCR (resistance → loss/heat), and shielding (shielded = less radiated noise).
  • Place close to the switch node; keep the hot loop small.

Ferrite beads (filtering)​

  • A ferrite bead looks like a small resistor at high frequency — it absorbs HF noise as heat. Rated by impedance at 100 MHz (e.g. "600 Ω @ 100 MHz") and DC current.
  • Common use: isolate a noisy digital supply from a sensitive analog/PLL/ADC rail (ferrite + caps = LC/RC filter).
Don't bead a fast digital rail blindly

A ferrite in series with a high-current or fast supply can resonate with decoupling caps and make ripple worse, or starve transient current. Use beads for filtering sensitive rails, not as a default on every power net.

Common-mode chokes​

  • Pass the differential signal, block common-mode noise — used on USB, Ethernet, and power inputs for EMI.

See also​