Author Topic: Ferrite beads in modern surface mount products  (Read 1149 times)

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Offline Dave TurnerTopic starter

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Ferrite beads in modern surface mount products
« on: November 28, 2018, 09:34:58 pm »
Hi all gurus,

With current emissivity rules and the almost universal use of surface mount componemts for modern designs; how are the issues once addressed by the addition of ferrite beads to a component's leg (amongst many other issues & solutions) dealt with on modern pcbs?

In the days of point to point (and/or dead bug) construction this was 'black magic' to the majority of hobbyists (and many professionals), which generally required a 'suck it and see' approach.

Interested to see any answers,

Dave


 

Offline dmills

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Re: Ferrite beads in modern surface mount products
« Reply #1 on: November 28, 2018, 10:01:46 pm »
There are plenty of ferrite beads available as SMT packages if you really need them (Sometimes useful for IO immunity and cleaning up switchmode supply ringing).

However with 4 layer boards not being the expense they once were you can usually throw a plane under your routing layer and minimise the loop area (and radiation) that way instead, modern logic being 2.5/1.8/1.5/1.2/1.0V does not hurt any either. 

Don't forget that to be a reasonable radiator the geometry has to be bigger then about 1/8th wave at whatever frequency matters, and SMT parts are usually rather small, this helps a lot.

Regards, Dan.
 

Offline Dave TurnerTopic starter

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Re: Ferrite beads in modern surface mount products
« Reply #2 on: November 28, 2018, 10:19:44 pm »
Dan

Understood - less energy - less crap - it's still black magic!

Cheers

Dave
 

Offline T3sl4co1l

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Re: Ferrite beads in modern surface mount products
« Reply #3 on: November 29, 2018, 06:24:03 am »
It's only black magic if you can't solve polynomial roots!

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
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Offline dmills

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Re: Ferrite beads in modern surface mount products
« Reply #4 on: November 29, 2018, 11:19:38 am »
And these days we got computers for that  ;D!

No magic, it is just that as the frequency rises it becomes ever more apparent that the DC rules apply at a point along the conductor, that a wire is a component too, and that you cannot ignore the parasitics.

Regards, Dan.
 


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