how to stope multiple postbacks on button click while using multiple user controls on same page ?

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C#

ASP.NET

Ajax

Hello friends,
I m using 5 different user controls on same page, i.e I have created
5 pages with .ascx files,having some text boxes on each page
their names are as
1. signup1.ascx
2. signup2.ascx
3. signup3.ascx
4. signup4.ascx
5. signup5.ascx
textbox of each .ascx file persorm some task on textChanged.
and m using these controls on page names as
signup.aspx which is my startup page of applycation, so when m typing some text on textbox of signup1.ascx file all the pages post back, I want that if m typing in textbox of signup1.ascx file then only this page should be post back, and other remains same