Download excel file with ajax

Hi to all, i'm new there and i have a big problem, i hope find answer here.
So i want to generate xsl file from database and download without reload page.

So this is my controller:

PHP Code:

   public function export()
    {
        $this->load->library("excel");
        $rowscount = $this->Public->Count();
        $object = new PHPExcel();

        $object->setActiveSheetIndex(0);

        $table_columns = array("Name");

        $column = 0;

        foreach($table_columns as $field)
        {
            $object->getActiveSheet()->setCellValueByColumnAndRow($column, 1, $field);
            $column++;
        }

        $users = $this->Public->export();

        $excel_row = 2;

        foreach($users as $row)
        {
            $object->getActiveSheet()->setCellValueByColumnAndRow(0, $excel_row, $row->username);
            $excel_row++;
        }

        $object_writer = PHPExcel_IOFactory::createWriter($object, 'Excel5');
        header("Content-Type: application/vnd.ms-excel");
        header("Content-Disposition: attachment;filename=Export.xls");
        $object_writer->save('php://output');
    } 


This is form in view:

PHP Code:

<form role="form" action="<?php echo site_url('admin/export')?>" method="post">
<button class="btn btn-warning">Export</button>
    </form> 


This is work correct, but before download start the current page reloaded. I want with ajax make download form work without reload page.

Any hint how to do that?

Regards.