Power Electronics

no ...i m designing solid state relay...for that i need zero cross circuit using tronsformer,coupler

Rectified AC into an opto coupler will give an waveform that goes to zero at the crossing point, this can be cleaned up to a digital signal to control whatever you like.
If that isn't detailed enough then you shouldn't be messing with high voltages!
Google 'optocoupler zero crossing detector' should yield plenty of results.
Del

There are really good resources available on the internet. Try Thyristor Device Data handbook DL137/D from On Semiconductor.

http://onsemi.com

International Rectifier (and other SCR, TRIAC and solid state relay suppliers) also do good manuals and application notes covering this too.

Also try an internet search for more information.