Electronics > Beginners

Ferrite beads in modern surface mount products

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Dave Turner:
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


dmills:
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.

Dave Turner:
Dan

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

Cheers

Dave

T3sl4co1l:
It's only black magic if you can't solve polynomial roots!

Tim

dmills:
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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