On 19 Apr., 22:31, "hrhofm...@[EMAIL PROTECTED]
" <hrhofm...@[EMAIL PROTECTED]
> wrote:
> On Apr 19, 11:07=A0am, default <edmoneyfromlanailstu...@[EMAIL PROTECTED]
>
> wrote:
>
>
>
>
>
> > On 19 Apr., 04:32, "hrhofm...@[EMAIL PROTECTED]
" <hrhofm...@[EMAIL PROTECTED]
> wrote:
>
> > > 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? =A0
>
> > 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. =A0But 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 ****blem 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 56dB=B5V and the spec is
about
> > 30dB=B5V, i am circa 26dB=B5V 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.. =A0Have 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)
|
