I want enter numbers into textbox and textbox would convert automatically these number into currency.(12,345,654)

I can use FilteredTextBoxExtender 

```
<ajaxToolkit:FilteredTextBoxExtender ID="ftbe" runat="server"
TargetControlID="TextBox3"         
FilterType="Custom, Numbers"
ValidChars="," />

```

But i want to automatically add commas when user enters number.