Hey guys. I'm currently designing a variable DC PSU to be used for general purposes. To enable the PSU to be used for multiple purposes, I'm going to use a double secondary transformer. For each of the outputs a full wave rectifier will be added. Then here comes the tricky part - I want to regulate the voltage of the PSU to be able to function as 2 separate/independent DC sources (fig. 1) and also regulate the voltage to function as a single dual-rail DC power supply (fig. 2).

It is easy to regulate each DC source if they where to stay independent with a simple Positive Adjustable Voltage Regulator, however the trouble is when the second configuration (fig 2) is used, the voltage is no longer stable. I thought of using a Negative Adjustable Voltage Regulator between the rectifier and V2-, but wont this affect the voltage regulation when using the sources independently again?

So if the question was not clear - How would I go about regulating the voltages for both types of configurations (fig 1 and 2)?

 

Either arrangement should work properly as long as each transformer winding/rectifier/voltage regulator is independent with no connections to other parts of the system.