How to protect battery from a power adapter?

[Switchy Cat]

I want to start building projects which will have the option to use a 9v battery and 9v power adapter.
I imagine a diode can protect the battery from the power supply.
Is that sufficient if both the battery and power adapter were connected by accident?

 

[Bluejets]

Would make more sense to ensure this cannot happen in the first place.
Years gone by, manufacturers would make the power supply inlet a self switchable unit (plug operates switch in the socket)

 

[Switchy Cat]

Would make more sense to ensure this cannot happen in the first place.
Years gone by, manufacturers would make the power supply inlet a self switchable unit (plug operates switch in the socket)

I believe you are correct. I will investigate this further, but it seems true that the plug has a mechanism that switches a contact off for the battery.

 

[Switchy Cat]

@Bluejets

This is confirmed. The jack has a built in mechanism. Thanks!

 

[kpatz]

A switched DC jack is ideal as mentioned. If you use diodes, you'd need one on the DC power input as well as on the battery. One to prevent the battery feeding into the DC jack (if the adapter is connected but unplugged), and another to prevent the DC input from feeding into the battery. You'd also need to make sure the DC adapter voltage is higher than the battery's, otherwise you'll still be drawing from the battery when the DC adapter is connected (higher voltage "wins").