Text box Changed event

I have a header file which contain a txt box and hyperlink(search) in a Asp.NET If i click hyperlink,It should go to Mainsearch screen with the value of txt box.Presently we don't have any event click for hyperlink.So i used txt_changed event for this.But it is not firing.It is firing in the double click..I set the property of txtbox as auto postback...Pls help me....I don't want to use linkbutton and image button for this .I am also using ajax controls in the application
...