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enter image description here

I'm trying to understand what ferrite bead he chose as shown in the picture. It says it is a 120R ferrite bead but from what I understand, when looking for a ferrite bead, you have to know the frequency you want to filter be in the resistive range on the component's ZRX chart.

So what frequency range is he filtering here? And is this the correct way to notate a ferrite bead, as opposed to labeling the component something like "60 Ω @ 50 kHz"?

I am a bit new to the electronics field so excuse me if I am missing something obvious. The schematic is from Phil's lab's YouTube channel showing how he made an amplifier with NE5532 op-amps.

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    \$\begingroup\$ You need a part number to be sure. \$\endgroup\$
    – Andy aka
    Dec 17, 2022 at 20:33
  • \$\begingroup\$ Is there no other way to figure out which one he would have likely chosen? I mean, otherwise it would be kind of pointless for him to put the 120R notation there \$\endgroup\$
    – elec
    Dec 17, 2022 at 20:37
  • \$\begingroup\$ vishay.com/en/inductors/ferrite-bead-calculator \$\endgroup\$
    – RemyHx
    Dec 17, 2022 at 21:06

2 Answers 2

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There are other parameters that are important for the component. Current rating, for example. Also package size. Not all of that stuff needs to be on the schematic.

100MHz is very commonly used as the frequency at which the impedance is specified for ferrite beads so omitting it does not subtract so much from the understanding of the schematic and makes it less cluttered. I would assume 100MHz unless otherwise specified, to be verified from the database of course if ordering parts or whatever.

Personally, I do put it on there, like "1K @ 100MHz" but Mr. Salmony appears to have less tolerance of clutter.

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  • \$\begingroup\$ Note that current rating is only a thermal figure. The impedance is measured at 0 DC bias, but drops quickly; a typical 0805 chip saturates with merely 50 to 200mA. \$\endgroup\$ Dec 18, 2022 at 6:47
  • \$\begingroup\$ The symbol looks like an inductor, but ferrite bead is not exactly an inductor like the one we would use in the circuit of SMPS. \$\endgroup\$
    – quantum231
    Jul 6 at 17:14
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The nominal impedance is usually specified @ 100 MHz. I agree that just labeling the ferrite bead with "120R" is not good practice and something like "120R@100MHz" would be a better way to do this.

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