Dual-rail power supply with parallel DC-DC converters?

[inventhouse]

I'd like to branch out into audio / synth circuits, many of which call for a dual-rail power supply.  I was wondering if I could build a simple one by connecting two little DC-DC buck converters with their inputs in parallel and one output set to half of the other. 

In theory 0/9v/18v looks a lot like -9v/0/+9v, but with how cheap and plentiful these little converters are these days I have to wonder why Instructables and the like aren't full of "plans" along these lines...  Of course, with how cheap they are, I might just pick up a six-pack and try it.

[Ian.M]

That wont work because the 9V output rail cant sink current from the 18V rail.

You can use *SOME* boost converters to generate a negative rail e.g. LM2596 based modules, however they need a stiff high current supply as input to start up successfully.  See: LM2596 buck module hacked for negative output

An other option would be to use a rail splitter with a floating 18V supply.  However that's a linear solution so if you need the derived ground rail to source or sink much current the rail splitter dissipation will be significant.  Search the forum from its main page for several topics about using them

[T3sl4co1l]

It works if you preload the one rail so its load current is always positive, or use a synchronous buck module that allows negative output current.

If you're making the converter yourself, you can also make a negative supply using a dual winding inductor.  The regulation won't be as good as two independent converters, but that's fine for most purposes.  (Same constraint applies, it must be synchronous or the positive output needs preload.)

Tim

[MasterT]

Buy isolated DC-DC converter, +5V -> +-15V
https://ca.mouser.com/ProductDetail/709-DPU01L-15