Use a TVS (Transient voltage suppressor) or "Tranzorb". It acts like a zener but has sharper reverse characterisrics. You could have used e.g. PSOTxx, only that these come in voltages of 8V, 12V or 15V.
Take a look at
http://www.us.st.com/stonline/books/toc/ds/index.htm
and see if...
Sometimes (or almost every time) it is very difficult to evaluate who the person asking the question is, what kind of answer he/her is looking for, and most important: What is REALLY the question?
As a suggestion I advise poeple to consider the following checkpoints when posting technical...
I guess one can talk about AC and DC ground in several contexts, but one context would be:
In a circuit there is an area which is confined between to common or differential mode inductors. The DC ground will be the same on either side, but the AC ground may not necessarily be the same.
