Ferrite Bead / Choke
A ferrite bead is a lossy inductor used to suppress high-frequency noise. Below its ferrimagnetic resonance it looks inductive (Z ≈ ωL); near and above resonance the ferrite becomes lossy and the impedance is mostly resistive, dissipating the noise. This tool gives a first-order estimate from a simple series R–L model, or converts a datasheet impedance-at-frequency point into an equivalent inductance. Approximate — real beads are described by a frequency-dependent complex permeability; always check the datasheet Z(f) curve.
Equations & Parameters ▸
\(X_L=2\pi f L \qquad |Z|=\sqrt{R^2+X_L^2} \qquad L_{eq}=\dfrac{|Z|_{datasheet}}{2\pi f}\ (\text{if } R\ll X_L)\)
| L | Low-frequency inductance of the bead (µH). |
| R | Loss resistance near resonance (Ω), optional. |
| f | Frequency (MHz). |
| Zds | Optional datasheet impedance point (Ω) at the frequency above, giving the equivalent inductance. |
Reference: Fair-Rite / Würth / TDK ferrite-bead application notes. Series R–L is a first-order approximation to the complex-permeability behaviour.
Inputs
µH
Below resonanceΩ
Resistive partMHz
Operating ptΩ
→ equiv. LResults
Series R–L model
Reactance XL—
Impedance |Z|—
From datasheet
Equivalent inductance—
Diagram