Try this:
list($day, $month, $year) = sscanf('12/04/2010', '%02d/%02d/%04d'); // field value
$datetime = new DateTime("$year-$month-$day"); // your format
echo $datetime->format('r'); // desired format
source: http://stackoverflow.com/questions/2621433/date-create-from-format-equivalent-for-php-5-2-or-lower