[SI-LIST] [SI-LIST]surge suppression
- From: "Emsys Sajith" <sajith_emsys@xxxxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Wed, 07 Jan 2004 15:21:05 +0530
Hi all,
The New year at our lab has kicked off with an interesting observation
We are in the development of an SMPS, the RFI filter section is built with =
discrete components
a common mode choke + 2class X caps + 2class Y caps
L)------------------I I---------------------(
__ I CM I __ INPUT TO SMPS
X --- I choke I X--- =20
N)=97---------------I_____ I---------(
___ ___
Y ----- Y -----
PE--------------------------------------------------
Hope the above figure makes the way they are connected=20
From left : the X cap across phase and neutral, then the common mode =
choke, the second X cap across phase and neutral and one Y cap each from =
Phase to Earth and Neutral to Earth.
Coming to the real issue :
While carrying out the surge test we injected 1.2/50us signal in both =
Phase and Neutral simultaneously
keeping earth as the return=20
( ie making it a common mode signal in P and N with respect to earth )
We observed that when 1.5KV is injected at the input , We are able to see =
around 2KV peak after the common mode choke=20
the common mode choke, which is suppose to suppress the common mode signal =
was seen to be doing=20
the opposite. Probing the point before CM choke was showing 1.5KV and just =
after it was 2KV
We tried removing the Y caps but it did not make any difference
The common mod choke is a standard part from a reliable manufacturer.
Can the common mode choke behave this way???
Could any one please explain what the phenomenon is????
Thank you for your time
Best regards,
Sajith
Analog Designer
IN.
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