DC to DC without shared GND

Is there a device, or can I make such a device, that allows me to take a 12v up to 4A DC supply into it and take out the same (or close to) voltage and current that does not share the same ground or power lines?

Links to information, products or schematics etc greatly appreciated.

Google on flybuck convertor.

No , I do not mean flyback.

useful when you need odd bias voltages

A warning though, there has to be some reference between the primary and secondary.

If totally isolated the secondary circuit potential can wander and i have sucessfuly blown the 3 kv breakdown of an opto isolator this way.

Possibly lethal consequences if there is enough energy storage also.

There are many fully isolated DC-DC converter modules on the market, for instance: http://uk.farnell.com/murata-power-solutions/uwe-12-6-q12p-c/converter-dc-dc-12v-6a/dp/1652245

The converter that MarkT suggested in reply #3, was based on you implying that you wanted one that was rated at the full current as your existing power supply.

However if you don’t need one rated at that much current, then there are converters that are much smaller and cheaper, such as this one.

You could use several of these if you need multiple isolated supplies.

There are are a whole range of converters with intermediate ratings/sizes.