Tv turns off by itself

My LG 60" plasma does the same thing if I have the power savings set to max during really dark scenes in movies or games. You may want to try adjusting that to see if your TV does the same.
 
My Sharp Aquios 65" did that when I first set up. In the menu; in system settings I found power options there were two "stand by" options once I turned then off it never would randomly power off on its own. Hope that helps you!