Magento: Get simple products of a configurable product

[php]
$productId = 7; //product id of configurable product

$_Product = Mage::getModel('catalog/product')->load($productId);
$simpleProducts = Mage::getModel('catalog/product_type_configurable')->getUsedProducts(null,$_product);

foreach(simpleProducts as $simple_product){

echo $simple_product->getId(); // Print Id's of all simple products
}
[/php]