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I am working on a project which requires the use of a boost converter to power a sensor which is read by a microcontroller. Both are powered from a battery. I know that when reading signals from a different device their grounds must be joined. That made me wonder if boost converters change what common ground is. I believe transformers do but these aren't the same thing. Looking at their schematics I would guess not but I want to be sure.

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    \$\begingroup\$ "Floating" or "isolated" is the term you are looking for. \$\endgroup\$
    – DKNguyen
    Jul 1 at 15:00
  • \$\begingroup\$ "Ground" is where ever you want to define it. It can be ANY node in the circuit. It's what YOU are calling the 'zero volt reference'. It's not some magical bucket to dump electrons in. Usually most components are referenced to 'ground', but you could just as easily call your VCC rail "ground" and call your ground "-VCC". You can even have more than one "ground" in a given circuit... AGND, DGND, etc... They may or may not be connected, depending on your needs. Ultimately, any component does not care what is called "ground", it only cares what voltages are presented to its own pins. \$\endgroup\$
    – Kyle B
    Jul 1 at 16:21
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There are isolated converters and non-isolated converters. Most are non-isolated converters. The module description or the circuit design description will tell you which it is. Usually they are non-isolating.

The output from an isolated converter will have a separate ground from its input. That lets you do fun things like connect the positive from the output to the ground of the rest of the circuit to generate a negative voltage (that kind of trick, of course, breaks the isolation.)

Isolated modules usually cost more and are a little more complicated to build. They have separate current loops for the input and the output sides. They often use transformers to galvanically separate the two loops.

Most common circuits and modules are non-isolated types. The ground on their input is connected to the ground of the output. They usually don't contain a transformer. There's a switched inductor, but no transformer. You can build a non-isolated converter with a transformer, and some circuits and modules do so.

With an isolated type, you would have to intentionally tie the grounds of your circuit together to, for example, measure the output voltage. That is much like what happens when you use a simple AC transformer.

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  • \$\begingroup\$ I have a follow up question. Can't it at times be problematic to tie grounds? Since voltage is a difference in potential, if the ground you are connecting to causes the absolute potential at the negative terminal to drop significantly couldn't that make the potential difference greater and change your voltage? For example making a 5V go to 6V? I guess I'm just wondering when is it safe to tie grounds? \$\endgroup\$
    – Nicokofi
    Jul 1 at 16:03
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No, a non-isolated boost does not isolate or "change" the ground. However if it's a flyback or transformer-based topology it could. In that case you can simply connect the input and output grounds together.

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