Hi Muhammad: The discussion on this thread has prompted me to think further about why I have not used integrated magnetics for NEBS applications in the past. My earlier response was based on what I could recall at the moment, and was only partially accurate.
If you use a device that has a 1500 VRMS rating, it will most likely have no trouble with the common mode surge, so that is probably not an issue. As Scott Lemon noted earlier, very little energy will get through the transformers on a common mode surge, so any protection on the secondary side will not have to deal with large currents that could upset your ground plane. I think the key concerns for using integrated magnetics are the differential lightning surge and the 120 VRMS power cross test. To pass the tests in GR-1089, the primary winding will have to survive a 100 amp, 2x10 uS differential surge. The small wire used in the integrated transformers may have trouble surviving this. Due to the fact that the primary side is not accessible outside the jack, you will not be able to put a sidactor across the primary winding to help protect it. The other issue you need to watch out for is the failure mode during the 120 VRMS power cross test. This test is applied through a "line simulator fuse" that must not blow open during the test. In other words, your primary side must fail open before the line simulator fuse opens. Compliance with this requirement is typically guaranteed by putting a fuse in series with the primary side, but with the integrated magnetics this is not possible. You will be depending on the fusing characteristics of the primary winding itself, which may be unpredictable. I think the above considerations are the ones you should evaluate carefully before committing to the use of an integrated magnetics jack. Failing either of these tests after the board design is complete would represent a major setback for your development program. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
