[sdiy] Using switching power supplies in series to get bipolar outputs?

Mattias Rickardsson mr at analogue.org
Mon Nov 20 18:30:42 CET 2023


Aha, thanks Guy for the clarification! :-)

/mr


Den mån 20 nov. 2023 17:46Guy McCusker <guy.mccusker at gmail.com> skrev:

> That sort of issue definitely happens if you try to use a positive
> regulator on a negative supply, e.g. attempting to regulate +/-15V to
> +/-12V by using a 12V regulator on the positive supply and a 3V
> regulator on the negative supply. The lower rail's regulator cannot
> sink current on its regulated output so if the +12V is sourcing more
> than the -12V is sinking then we have a problem.
>
> With two separate 12V supplies in series this is not an issue and I
> haven't been able to cook up a scenario where it becomes a problem.
> It's also not a problem to hook up in series two 15V supplies each
> regulated to 12V by a positive regulator. And actually that tends to
> be how dual-output lab supplies work, if I am not mistaken.
>
> On Mon, Nov 20, 2023 at 3:24 PM Mattias Rickardsson <mr at analogue.org>
> wrote:
> >
> > Wasn't there something with the sinking/sourcing of current that
> introduced some potential (no pun intended) problem when using two positive
> supplies as a bipolar supply?
> >
> > Can't seem to remember the details or where I heard it right now.
> >
> > /mr
> >
> >
> >
> > Den mån 20 nov. 2023 13:43Roman Sowa <modular at go2.pl> skrev:
> >>
> >> But hooking them up in series to get higher voltage actually IS making a
> >> bipolar supply. It only depends which node you decide is the 0V. The
> >> outputs are isolated from AC inpt so you can do whatever you want with
> >> multiple outputs up to the isolation limit which is if I'm not mistaken
> >> up to 3kV
> >>
> >> Roman
> >>
> >> W dniu 2023-11-18 o 15:08, Scott Bernardi via Synth-diy pisze:
> >> > I've noticed that most switching power supplies that offer bipolar
> >> > outputs(i.e., to get +/-12v) have less current capability on the
> >> > negative supply than the positive.  For example, the Meanwell 65B
> which
> >> > has +/-12v and +5v, great for Eurorack, has
> >> > +5v max 8 amps
> >> > +12v max 3.5 amps
> >> > -12v max 1 amp
> >> > What about buying two +12v supplies, or maybe one that has +12v and
> +5v
> >> > with another with just +12v, and hooking them in series with a center
> >> > tap to get +/- 12v?
> >> >
> >> > This article
> >> >
> https://www.mouser.com/pdfDocs/blog_how-to-operate-parallel-and-series-connection.pdf
> <
> https://www.mouser.com/pdfDocs/blog_how-to-operate-parallel-and-series-connection.pdf>
> looks like it's possible, although they only talk about hooking them up in
> series to increase the output voltage rather than bipolar.
> >> > Has anybody done this?
> >> >
> >> >
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