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I am designing a simple digital circuit on a PCB that includes a power supply that provides +24V and -24V, but there is no ground. I am assuming that the negative voltage (-24V) is ground? What about the IC's that use a GND pin?

I plan on using a 2-layer board with the bottom layer as "ground", but what is "ground" in this case?enter image description here

I have included the schematic. In the schematic is a +24V and -24V power supply that supplies the power to the DC/DC converter, and the converted voltage to the IC - but this IC uses GND, and I am not sure where GND is from? Or what the common is for the DC/DC converter?

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    \$\begingroup\$ Why did you delete your previous, almost identical, question? All of the comments and discussion for that question have been lost now. \$\endgroup\$
    – Elliot Alderson
    Commented Jan 3, 2022 at 20:08
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    \$\begingroup\$ Looks like you're missing the return connection from each of your 24 V power supplies. They should be tied together and become the GND for your circuit. Can you provide more info on those power supplies? A front panel picture or a data sheet reference. \$\endgroup\$
    – SteveSh
    Commented Jan 3, 2022 at 20:08
  • \$\begingroup\$ Refer to the datasheet for your DCWN06B-15 DC/DC converter and you'll find that its maximum input voltage is 36V. This means that your schematic is poorly/ambiguously labelled with "+24V" and "-24V", since this implies a 48V supply - which would clearly violate the maximum of the DC/DC converter. So you do not have "a power supply that provides +24V and -24V" - you have a single 24V supply. \$\endgroup\$
    – brhans
    Commented Jan 3, 2022 at 20:21
  • \$\begingroup\$ And sine the DCWN converter is isolated, you do not need to reference either of the "+24V" or "-24V" inputs to the GND net of the rest of the circuit - although considering the reverse-polarity protection section created by Q1 & Q2, should probably should just choose one as GND and connect it (I would choose "-24V" for the sake of my sanity). \$\endgroup\$
    – brhans
    Commented Jan 3, 2022 at 20:22
  • \$\begingroup\$ mali101 - Hi, As commented already, by starting this new question which is basically a simplified repeat of your previous one, site members here have not seen the previous comments which were added there and which might be helpful to them (even if you don't think so). Part of the "Stack Exchange philosophy" is that questions should be edited to improve them. Please do not repost effectively the same question multiple times. \$\endgroup\$
    – SamGibson ♦
    Commented Jan 3, 2022 at 21:58

4 Answers 4

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The DCWN06B-15 is an isolated DC/DC converter.

B means ìt takes in 24 to 36 volts, so what there is labeled as +24V and -24V may not be +24V and -24V after all, it is likely to be 24V and return for 24V. Or then it is a wrong module which should have 48V rated input.

The module has isolated dual output so it will generate +/- 15V output in reference to the COM terminal.

So unless there is no further clues about the 24V supply, it is not DC referenced to isolated output ground, as it has only common mode AC reference to isolated output ground.

Which means the FETs to provide protection from incorrect input polarity makes little sense as it has gates connected to isolated ground.

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  • \$\begingroup\$ I am confused about the DC reference to isolated output ground part. But in any case you're right... \$\endgroup\$
    – mali101
    Commented Jan 3, 2022 at 20:50
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The datasheet for the DCWN06B states that its input voltage range is 18 -36 Volts, and that its output is isolated from the input.

So, the module requires a single 24 volt power supply which does not need any connection to the output side of the module. It is fairly common, but misleading, to lable the two terminals of a 24 volt power supply as "+24V" and "-24V" - if there is no indication of Zero volts or Ground, you can usually assume that this indicates a single 24 volt supply.

The Common terminals on that module are the Ground/Zero volt terminal for the output side of the supply.

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Just thinking out loud... when they actually show you +24 V and - 24 V they are referring to something, that will be the 0 V and that would be your GND. You would have 48 V between +24 V and - 24V. You have 3 leads coming in.

It would not be the 24 V as explained.

And then your output of ± 15 V would be referenced to that same ground.

Now, for the life of me why do you need a bipolar power supply when you just need a single 11.4VDC to 36VDC as per the manufacturer of the 10 V voltage reference...

And I am hesitant to ask for the function of the series switching MOSFETS that do not switch anything.

But it's been a while for me...about 40 years...

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By definition, ground (GND) is 0V. So -24V is not ground.

It sounds like you have a 48V power supply, which isn't going to work as it stands.

There are techniques for creating a ground that's halfway between two voltage rails, but that's an extra bit of circuitry.

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