populate textbox on dropdownlist change

Hi
I am trying to populate textbox on dropdownlist change. but it it is refreshing the page due Autopostback = "true" Please let me know if there is anything i am missing or there is another alternative.
<asp:DropDownList ID="ddl_ship_from" runat="server" Width="275px" CssClass="width155"
                                        OnSelectedIndexChanged="ddl_ship_from_SelectedIndexChanged" AutoPostBack="true">
                                    </asp:DropDownList>
protected void Page_Load(object sender, EventArgs e)
        {
  ...