On Apr 18, 3:09=A0am, default <edmoneyfromlanailstu...@[EMAIL PROTECTED]
>
wrote:
> I am writting at my diploma thesis with an EMC theme.
>
> If got a power fan (13V / 6A) witch produces conducted emissions, so I
> have to reduce them to achieve CISPR25.
> Up to 40MHz I found an easy solving with LC lowpass filter, but over
> 50MHz I am out of the CISPR25 limit.
>
> Does anybody have experiences in EMC design in high frequency bands,
> doesn't have?
>
> I think about solving it like the motherboard producers do, they
> design there signals like little inductors and so one.
> But I didn't find any guidlines to do this like them.
Are you saying that the lowpass filter is not blocking the high-
frequency noise components above 45 MHz, but is blocking the mid-range
frequency components below 45 MHz, and so you need a more effective
filter against the really high-frequency noise from 45 MHz and
higher? Some ferrite beads on the power leads along with shunt
capacitance between the leads and between each lead on a good solid
ground should form an effective high-frequency filter. But lead
lengths are critical at these frequencies, beware of any leads longer
than 1 inch, these look as much like inductors as real inductors.
How many dB are you over the limits, 10, 100???
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