...there are topologies, and modules, which already have both the +/- output voltages.
I took a quick look at the dual output modules that are available from Mouser and most of them have a fixed output voltage with standard values: 15V, 20V, 24V. This menas that I can't feed and LDO with 17V and get a clean 15V after it.
So it seems that it's either two modules or complete custom solution.
The only time I've had to synchronize regulators was for a project with a class-D amp power supply. I used the LM2588 boost regulator.
Well, this is very promising. No need to sync chips simplifies the task a lot.
What is the motivation behind independent supplies versus one common supply and load switches? Do the loads need to be switched at all?
The motivation is very simple. Imagine a system that has several different audio modules powered from a single source. The set of modules may differ from system to system. All these modules have different power requirements. One may need just a +24V rail while another needs +/-15V and still another needs +/-30V. Now, I can feed my +/-40V unregulated DC and get +/-30V rails with reasonable power dissipation. Even 24V may be managable. But to get +/-15V working I have to resort to dropping resistors which is not the best solution.
I need to choose the optimal topology for this task. Since I have two rails it may be benefical to use one of them as a positive and another one as a negative. The disadvantage (as I see it) is that I need 2 SMPS chips to do the work. Another solution is to use something like the method described here:
http://www.ti.com/lit/an/slva369a/slva369a.pdfBut I doubt I can feed it with 40V and get +/-30V out of it.
Another question is what to do with grounds. With 2 chips solutions it seems pretty straightforward. But with a split-rail system - I can't wrap my head around this. Can I establish the common ground point for all modules in the system?