I have a number of devices in which I want to incorporate a connector with 3 input pins, 1,2,3. and 2 output pins a,b
When the charger is not plugged into the port, 1 & 2 are output on a,b , and these would be connected to the battery. So the device would run on battery power taken from a,b.

When the external charger is connected, 2,3 are active. since only 1,2 are connected to output a,b - the device now does not get any power.

3 is tied to the battery, so now the charger would just charge the battery and the device would be off.

I read about it here - but language turned out to be a big barrier..

http://www.dealextreme.com/forums/Forums.dx/Forum.0~threadid.352315

Any ideas what could work ? Essentially this connector has a mechanical switch that changes contacts if the charger is plugged in..

 

Many DC power jacks have a NC switch included that opens as an external source is plugged in.

Check Mouser's part#16PJ221 as an example.

 

that is indeed what i was looking for. Any idea how the connections would work ?

 

A jack plug breaks the contact of a normally closed switch.
Miniature jack plugs and jacks. All are 3.5 mm except the gold-plated plug, which is 2.5 mm. All the jacks are two-conductor (TS). The tan-colored jacks have a normally-closed switch.

Panel-mounting jacks are often provided with switch contacts. Most commonly, a mono jack is provided with a single normally closed (NC) contact, which is connected to the tip (live) connection when no plug is in the socket, and disconnected when a plug is inserted. Stereo sockets commonly provide two such NC contacts, one for the tip (left channel live) and one for the ring or collar (right channel live). Some designs of jack also have such a connection on the sleeve, as this contact is usually ground it is not much use for signal switching but could be used to indicate to electronic circuitry that the socket was in use.

Less commonly, some jacks are provided with normally open (NO) or change-over contacts, and/or the switch contacts may be isolated from the connector.

The original purpose of these contacts was for switching in telephone exchanges, for which there were many patterns. Two sets of change-over contacts, isolated from the connector contacts, were common. The more recent pattern of one NC contact for each signal path, internally attached to the connector contact, stems from their use as headphone jacks. In many amplifiers and equipment containing them, such as electronic organs, a headphone jack is provided that disconnects the loudspeakers when in use. This is done by means of these switch contacts. In other equipment, a dummy load is provided when the headphones are not connected. This is also easily provided by means of these NC contacts.

Other uses for these contacts have been found. One is to interrupt a signal path to enable other circuitry to be inserted. This is done by using one NC contact of a stereo jack to connect the tip and ring together when no plug is inserted. The tip is then made the output, and the ring the input (or vice versa), thus forming a patch point.

Another use is to provide alternative mono or stereo output facilities on some guitars and electronic organs. This is achieved by using two mono jacks, one for left channel and one for right, and wiring the NC contact on the right channel jack to the tip of the other, to connect the two connector tips together when the right channel output is not in use. This then mixes the signals so that the left channel jack doubles as a mono output.

Where a 1/8″ or 3/32″ jack is used as a DC power inlet connector, a switch contact may be used to disconnect an internal battery whenever an external power supply is connected, to prevent incorrect recharging of the battery.

A three-conductor signal input socket is used on some battery-powered guitar effects pedals to eliminate the need for a separate power switch. When the user plugs in a two-conductor guitar or microphone lead, the resulting short-circuit between earth and ring connects an internal battery to the unit's circuitry, ensuring that it powers up or down automatically whenever a signal lead is inserted or removed. A side effect is the risk of inadvertently discharging the battery if the lead is not removed after use, for example if equipment is left connected overnight.