How to keep MacBook awake with lid closed + extended display?
Requirements for closed-display mode from, Use your Mac notebook computer in closed-display mode with an external display:
To use closed-display mode with your Mac notebook, you need:
- An AC power adapter
- An external keyboard and mouse or trackpad, either USB or wireless
- A USB-C to USB adapter if you're using a USB mouse or keyboard with MacBook (Retina, 12-inch, Early 2015) and later or MacBook Pro models introduced in late 2016
- An external display or projector
If you're using a USB keyboard and mouse
- Make sure that your Mac notebook is plugged in to an outlet using the AC power adapter.
- Connect a USB keyboard and mouse to your Mac.
- With your Mac turned on and the display open, connect the Mac to the appropriate port on the external display or projector and turn the display or projector on.
- Use an appropriate Apple video adapter if necessary.
- After your Mac notebook's Desktop appears on the external display, close the computer's lid. When you close the lid: In OS X Lion v10.7 and later, the external display changes to a blue screen, then shows your Desktop. In OS X v10.6.8 and earlier, you can wake your Mac by clicking the mouse button or pressing a key on the external keyboard.
You can now use your Mac notebook as you normally would with a USB keyboard and mouse.