pdo disconnect from database in class - php

Question

I wrote a class for PDO and need to disconnect PDO => ( I don't know how to do it )
I don't know code wrote is structurally correct?!
use $this->returnconn(); for db connection
Please guide me...
Sample code:
class conn {
public $inner;
public function returnconn() {
$CONF = $TMPL = array();
// The MySQL credentials
$CONF['host'] = 'localhost';
$CONF['user'] = 'root';
$CONF['pass'] = '';
$CONF['name'] = 'cmss';
$dsn ="mysql:host=".$CONF['host'].";dbname=".$CONF['name']."";
try{
$conn = new PDO($dsn,$CONF['user'],$CONF['pass']);
$conn ->exec("SET CHARACTER SET UTF8");
}catch(PDOException $e){
die($e->getMessage());
}
return $conn;
}
public function select(){
switch ($this->inner->switch){
case "select":
$sql="SELECT ".$this->inner->todo." FROM ".$this->inner->table." WHERE ".$this->inner->sql."";
$result=$this->returnconn()->prepare($sql);
/*
* this->returnconn();
*/
$result->execute();
if($result->rowCount()<=0){
return '{"msg":"empty "}';
}else{
return $result->fetch(PDO::FETCH_ASSOC);
}
break;
}
}
}
/* receive data */
$obj = new conn;
$iner = array();
$iner['table'] = 'category';
$iner['switch'] ='select';
$iner['todo'] = '*';
$iner['sql'] = '`id` IS NOT NULL ORDER BY `id` ASC';
$in = json_decode(json_encode($iner));
$obj ->inner = $in;
echo json_encode($obj ->select());
Do need a function to disconnect?