Re: reducing Conducted Emission from Power Fan in high frequency band over 50MHz

On 19 Apr., 22:31, "hrhofm...@xxxxxxx" <hrhofm...@xxxxxxx> wrote:
On Apr 19, 11:07 am, default <edmoneyfromlanailstu...@xxxxxxxxxxxxxx>
wrote:





On 19 Apr., 04:32, "hrhofm...@xxxxxxx" <hrhofm...@xxxxxxx> wrote:

On Apr 18, 3:09 am, default <edmoneyfromlanailstu...@xxxxxxxxxxxxxx>
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?  

yes that's my problem, downsides 45MHz it's okay

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.

i tried two X-C's form plus load to case of the fan and one from gnd
to case, it works fine but the porblem is that i can't do it.
according to the opnion of my boss, because maybe there are new fans
designed in future that doesn't have a metallic case.

How many dB are you over the limits, 10, 100???

the worst case level is about 65MHz with 56dBµV and the spec is about
30dBµV, i am circa 26dBµV above the debit level- Hide quoted text -

- Show quoted text -

If the new fans of the future have plastic cases, they will have to do
a better job inside the case of stopping the noise..  Have you tried
any ferrite beads on the conductors on the fan side of the capacitors
to act as high impedances to the higher frequency noises?- Zitierten Text ausblenden -

- Zitierten Text anzeigen -

did you mean like this?:








|---------'
| |
C| |
Ferrit C| |
C| |
| |
| |
--- |
CY --- |
| |
| |
| |
| .-.
o-------o X )FAN
| '-'
--- |
CY --- |
| |
| |
| |
C| |
Ferrit C| |
C| |
)---------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
.

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