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What is the distinction between a ferrite bead (as an SMT component) and an inductor?

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  • \$\begingroup\$ Your average inductor has much higher inductance than a ferrite bead. You do need to provide your own wire with the ferrite bead though. \$\endgroup\$
    – winny
    Commented Feb 18, 2022 at 21:20
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    \$\begingroup\$ They have mutually exclusive applications. Like a biscuit and a piece of paper. But, you can make an FB from an inductor just like you can wrap a biscuit in paper. \$\endgroup\$
    – Andy aka
    Commented Feb 18, 2022 at 21:31
  • \$\begingroup\$ @winny Pray tell in e.g. (1st result) aliexpress.com/item/32854666740.html where I 'provide my own wire'? \$\endgroup\$
    – OJFord
    Commented Feb 18, 2022 at 21:44
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    \$\begingroup\$ Your link is not a ferrite bead but rather a chip inductor. Please use reputable sources. Ali is not one of them. \$\endgroup\$
    – winny
    Commented Feb 18, 2022 at 21:59
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    \$\begingroup\$ I’d be darned. I need to pay more attention to these trends. The term ferrite bead just a few years ago referred this type of device: we-online.com/catalog/en/WE-SAFB \$\endgroup\$
    – winny
    Commented Feb 18, 2022 at 22:33

1 Answer 1

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Technically, a ferrite bead is an inductor but it is designed to be a very lossy one. Ferrite beads are designed to 'soak up' high frequencies and are specified with an impedance at a given frequency. eg. 100 Ohm @ 100MHz. The other critical spec is the current. If you exceed the rated current on a FB it becomes just a piece of wire electrically - the ferrite becomes saturated and stops doing what it should do.

Ferrite beads are normally used on power rails and signals to/from the outside world to soak up differential noise for EMC reasons. Sometimes you'll see them on a clock signal to slow down the edges a little, again for EMC reasons.

Just for completeness, ferrite beads ( as opposed to the SMT ones the OP mentions) are found on various data cables, again for EMC reasons. On diode leads in switchmode supplies to 'quieten' the 'snap' when the diode suddenly starts conducting for EMC reasons.

Note that you can also get ferrite beads that aren't designed to be lossy and can be used to construct inductors and transformers - so the context in which we use the term 'ferrite bead' is important.

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