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I'm looking to build a 3 rail regulated supply (+5v, +-12v) and I've got a bunch of cheap but functional buck converts from aliexpress. I'm wondering if I can run these off a single AC-DC converter (wall wart, etc) and get a common-ground 3 rail supply from this?

I'm thinking something like:

schematic

simulate this circuit – Schematic created using CircuitLab

Will that work? Or do I need to introduce a multi-tap transformer or similar solution? The buck converters are these.

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    \$\begingroup\$ the GND in and GND out are probably shorted together \$\endgroup\$ – jsotola Jan 10 '18 at 5:32
  • \$\begingroup\$ According to the link, 'non-isolated step-down module', so the GND in and out are definitely shorted together. \$\endgroup\$ – Whit3rd Jan 10 '18 at 8:48
  • \$\begingroup\$ Hmm.. seems stack exchange has no limit on user handles... LOL \$\endgroup\$ – Trevor_G Jan 10 '18 at 14:51
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The circuit will not work unless either

  • the -12V converter is an isolated DC-DC converter, or
  • it is intended to produce negative voltages and actually has a positive GND contrary to your labeling.

Cheap converter modules that don't specify otherwise are likely to be non-isolated. This means that the input negative/GND and the output negative/GND are internally connected, so your circuit will short out the -12V converter.

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  • \$\begingroup\$ That's what I was afraid of. Think I'm just going to get a dual-rail linear +/-12v supply and throw an LM7805 on the +12 for my third rail. \$\endgroup\$ – Trevor Jan 11 '18 at 15:17
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That's exactly how they are meant to be used and yes they will work like that. Of course, you get what you pay for so you never know how stable those regulators are, or if they can safely meet the specs they claim to support.

Of course your -12V regulator needs to be an actual inverting regulator as I don't think it will work by simply flipping the outputs of a 12V regulator around.

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