What does this diagram mean?

[Swivelguy2]

This is the wiring diagram for a DC power jack:

Here's the jack itself, and the complete spec sheet:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=1442626&k=cp-6-nd
http://www.cui.com/GetSpecForDigiKey.aspx?MFGNum=PJ-005B

My question is: what exactly is the relationship between pins 2 and 3 there? If I'm going to run current through pin 1 and then return it to either pin 2 or 3, which one should I use?

 

[PottedMeat]

When you don't have a plug in the jack, pins 2 and 3 are connected. When you have a plug inserted pin 2 is connected to the plug and pin 3 is disconnected. You can use it to separate 2 power sources.


See Closed-Circuit DC Power Jacks section on this page:
http://tangentsoft.net/audio/pancomp.html

 

[Swivelguy2]

Thanks, I think I get it. I want to use Pins 1 and 2 then, and just leave 3 unwired.

 

[Paperdoc]

For use as a power input jack, the matching plug on the end of the cord will be a male tip / sleeve type. The sleeve will make contact with terminal #1 in the jack. This will go to one side of the device's power consumption system, probably to a combined circuit Ground and power Ground. The tip will contact terminal #2, and in doing so will disconnect #2 for #3. So the power input is coming in on term #2 and that terminal should go to the power consumption point in the device - maybe the + side of the circuit, if it is designed to have a negative Ground. IF the device has an alternative power supply like a battery, that supply would have one side of it connected to the same place as Terminal #1 (Ground, maybe negative), and its + output connected to Terminal #3 so that its power is available to the circuit when the jack is NOT plugged in. However, when the external jack is plugged in two things should be noted. One is that the battery supply is disconnected so that, if the external supply module is not providing power, the device has no power and is completely dead - there is no automatic battery backup with such a simple circuit. The other is that so far there has been no discussion of a way to use power from the external supply to recharge the hypothetical battery. That is a separate circuit design consideration.