require_once 'Config.php';

abstract class DB {

    private static $instance;

    public static function getInstance() {
        if (!isset(self::$instance)) {
            try {

                self::$instance = new PDO('mysql:host=' . DB_HOST . ';dbname=' . DB_NAME, DB_USER, DB_PASS);
                self::$instance->exec("set names utf8");
                self::$instance->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
                self::$instance->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_OBJ);
            } catch (Exception $e) {
                echo $e->getMessage();
            }
        }
        return self::$instance;
    }

    public static function prepare($sql) {
        return self::getInstance()->prepare($sql);
    }

    public static function closeConnection(){
        try {
            self::$instance = null;
        }
        catch (PDOException $e){

            die($e->getMessage());
        }

    }

}

<?php
require_once 'DB.php';

Class CrudProfissao extends DB {
    public function findAll(){}
    ...

    public function __destruct() {
        DB::closeConnection();
    }

}