“The Constitutional Convention of 1787 is supposed to have created a government of ‘separated powers.’ It did nothing of the sort. Rather, it created a government of separated institutions sharing powers.” -Richard Neudstadt
In addition to separation of powers, the Framers crafted a government of limited powers by creating a system of checks and balances to ensure that each branch had some control over the others and that no one branch could ever have complete control. Here are a couple websites that explain checks and balances along with a few examples.
Social Studies Help Center: How does our system of checks and balances help limit power?
US Constitution Online: Constitutional Topic--Checks & Balances
American System of Checks & Balances
Checks and Balances: Internal Constraints on Government Power
The charts and videos below help illustrate how the system works with specific checks.