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I found an AC adapter that converts 230V 50hz AC to +16V, 0V, 32V (3 pins) DC. I wanted to convert this into a +12V, -12V dual power supply. Someone suggested that I use a positive buck converter to create the +12V but he told me that I would not be able to create a -12V by just using the same technique; a buck for 32V and connect the terminals in reverse for -12V

I didn't get why this is true.

schematic

simulate this circuit – Schematic created using CircuitLab

Physically, if I have two 1 V batteries, how should I connect the second battery to get a -1V at node 2. Afaik I would just flip the terminals of the second battery like circuit A, but how is this any different from circuit B? Is circuit A even right? Else how would I get a negative voltage with a +1V battery at node 2? In other words, practically, how would I ensure a ground in the middle?

Here's the nameplate of the AC Adapter: https://i.sstatic.net/zAIbo.jpg

Edit: I replaced the transistor with a box with 2 nodes, node 1 requires +1V and node 2 requires -1V

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  • \$\begingroup\$ I don't have a lot of hope that the effort can produce results for you here, but can you open up the adapter and provide us with as much detail as possible about what you find inside? \$\endgroup\$
    – jonk
    Commented May 7, 2021 at 3:14
  • \$\begingroup\$ @jonk Heres the label imgur.com/a/K1VXz8X \$\endgroup\$ Commented May 7, 2021 at 3:50
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    \$\begingroup\$ Not with your basic non-isolated buck converter, but you can use any old isolated dc-dc converter to do the job. \$\endgroup\$
    – Hearth
    Commented May 7, 2021 at 3:56
  • \$\begingroup\$ @Hearth ignore the buck for a moment, Is circuit A correct for the intended purpose ? \$\endgroup\$ Commented May 7, 2021 at 3:58
  • \$\begingroup\$ @AravindhVasu It's unclear what your intended purpose is. If you just want to have three nodes, with one volt between each adjacent pair, then yes (but if that's how you have your transistor connected, you're just going to fry it!) \$\endgroup\$
    – Hearth
    Commented May 7, 2021 at 4:00

1 Answer 1

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Following doesn't answer how to connect your converters to get -12 V.

I would not be able to create a -12V by just using the same technique; a buck for 32V and connect the terminals in reverse for -12V. I didn't get why this is true.

Confusion arises since you have assumed that the 12 V converters are devices which have only two terminals. They actually have 4 terminals. Two of those terminals (reference or 0V terminals) may be shorted inside the converter (left side picture). See the diagram below. If you connect the 12 V of one such converter and 0 V of another together, you are effectively shorting the 12 V and 0 V of the same converter together.

If the input and output of the converter are isolated from each other, this type of short doesn't occur (right side picture). A common way the input and output terminals are isolated is via transformers. There is (usually) no electrical connection between the primary side and secondary side; the connection is magnetic.

See the diagram below.

converters with and without isolation

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  • \$\begingroup\$ After writing this answer, I realise that your proposed connection may be different. However, if you were to draw a similar diagram, i think you could figure out if a short circuit will exist for that configuration or not. \$\endgroup\$
    – AJN
    Commented May 7, 2021 at 10:27

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