[SI-LIST] Re: help: the ground under transformer and common mode choke

Steve,
Thanks.
I don't understand your second part. Do you mean the noise is come from line
side ?
I draw a picture to indicate what I want to do to avoid unwanted noise
coupling to the signal lines.
Does this do help ?
Does this implemented yours'  "Voiding logic ground in the vicinity of
magnetics "?
Best Regards,
Qingnan
 <<hole in ground.doc>> 

-----Original Message-----
From: steve weir [mailto:weirsp@xxxxxxxxxx]
Sent: 2004?5?20? 17:24
To: zhangq@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: help: the ground under transformer and common mode
choke


The goal is to avoid unbalanced coupling of CM noise from logic ground into 
the line side of the magnetics, not to attempt to isolate logic ground from 
chassis.  The latter will create even more noise that you will need to 
isolate from the line side of the magnetics.  Voiding logic ground in the 
vicinity of magnetics is one way to reduce the possibility of unequal 
coupling. You should place your magnetics and set your clearances 
accordingly.

Regards,


Steve.

At 03:58 PM 5/20/2004 +0800, Zhang, Qing Nan (Qing Nan) wrote:
>Dear All,
>We know that the circuit ground and power plane is noisy. Thus we avoid to
>extend the circuit ground and power plane under the transformer and common
>mode choke to avoid RF emission.
>Does it do hlep when we make some holes in the ground plane under the
>transformers and chokes ?
>
>Thanks,
>Qingnan
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