public function export_data($data = array())
    {
        # code...
        include_once(APP_PATH.'Tools/PHPExcel/Classes/PHPExcel/Writer/IWriter.php') ;
        include_once(APP_PATH.'Tools/PHPExcel/Classes/PHPExcel/Writer/Excel5.php') ;
        include_once(APP_PATH.'Tools/PHPExcel/Classes/PHPExcel.php') ;
        include_once(APP_PATH.'Tools/PHPExcel/Classes/PHPExcel/IOFactory.php') ;
        $obj_phpexcel = new PHPExcel();
        $obj_phpexcel->getActiveSheet()->setCellValue('a1','Key');
        $obj_phpexcel->getActiveSheet()->setCellValue('b1','Value');       
        if($data){
            $i =2;
            foreach ($data as $key => $value) {
                # code...
                $obj_phpexcel->getActiveSheet()->setCellValue('a'.$i,$value);
                $i++;
            }
        }   

        $obj_Writer = PHPExcel_IOFactory::createWriter($obj_phpexcel,'Excel5');
        $filename = "outexcel.xls";

        header("Content-Type: application/force-download");
        header("Content-Type: application/octet-stream");
        header("Content-Type: application/download");
        header('Content-Disposition:inline;filename="'.$filename.'"');
        header("Content-Transfer-Encoding: binary");
        header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
        header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
        header("Pragma: no-cache");
        $obj_Writer->save('php://output');
    }