I have a battery powered device and I want to add a DC jack. I am using a simple diode or gate to switch between the two. Of course this leaves me with one negative return from the device but two power inputs to return to. Do I simply split the V- return or is it more complicated?

I know this is really basic, but I am new with a lot to learn (as the last few hours of searching these forums for an answer has proven).

 

Wire the returns together.

Use a couple of Schottky diodes to OR the battery with the alternate power input.

A 1N5817 through 1N5819 will work OK for <= 1A current. However, if you're above perhaps 500mA current, go for a 1N5820 through 1N5822; they're rated for up to 3A continuous, and you'll have a lower Vf.

 

Thanks. I thought it was that simple but wanted to be sure. I am using 1N4001 diodes. The current is only about 20mA so it should be fine.