Download Database Back_up using Codeigniter

//Backup manually
    public function CI_db_backup() {
        // Load the DB utility class
        $this->load->dbutil();
        $this->load->database();
        $dbName = $this->db->database;
        $prefs = array(
            "format" => 'sql', // gzip, zip, txt
            "filename" => $dbName.'.sql', // File name 
        );

// Backup your entire database and assign it to a variable
        $backup = $this->dbutil->backup($prefs);

        $folder = FCPATH . "/storage_db/db_backup/";
        $date = date("m-d-Y-H-i-s", time());
        $filename = $dbName . "_" . $date . ".sql";
// Load the file helper and write the file to your server
        $this->load->helper('file');
        write_file($folder . $filename, $backup);

// Load the download helper and send the file to your desktop
        $this->load->helper("download");
        force_download($filename, $backup);
    }