Ground Nets with multiple voltages

Electronics
#1

So, this may be a dumb question, but in my current project, there are 3 different currents- 5V, 12V and 24V, all running separate things. Is there any reason I can’t tie the grounds together in these? It makes it a lot easier to wire, but I am wondering if there is a reason people don’t do that more.

For instance, I have a 5V voltage regulator, which has 12V and Gnd IN and 5 V and Gnd OUT, I take that ground and just connect it back to the 12V GND, so effectively theres just one wire coming out. I have the logic circuit wired up to the same ground as all three nets. There is a 12V supply and 24V supply independent of each other, and that 5V regulator for the logic circuit.

Could there be any damage? Especially to the logic circuits.

#2

If all three are isolated from the mains, there should be no problems.

#3

Mains as in AC?

Should I put diodes anywhere in there? I don’t really want the voltage drop and the extra effort if I have to though.

#4

No there isn’t, and unless you have a reason not to doit it, it is generally a good practice.

If you have both digital and analog, it is a good idea to have all digital on a common ground, and all analog on a common ground, then have a single tie point between the two.

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#5

Great, thanks guys. As usual, I appreciate the electronics help.

#6

Ground is ground the world around. And as pointed out unless there is a good reason to isolate a circuit it’s best that you use a common ground. An isolated circuit (or floating ground) can have a difference in potential from it to the other circuits, developing a “Ghost voltage”.

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#7

I strongly agree with Andrew’s commons about best practice on separating analog and digital grounds.

When using multiple 3 terminal regulators from a single supply voltage it is often helpful to add a 1uf tantalum and a .01 uF ceramic disc across the output terminal to ground. The circuit layout should place these parts as close as possible to the 3 terminal regulator.

This helps with noise reduction considerably.
If you are laying out a PCB board (and choosing trace width) or picking a wire gauge for point to point wiring, you should remember the the common ground should be able to handle enough current for all three supplies that are tied to common ground.

#8

I have some 0.01 and 0.1 ceramic caps, but other than that I just have a collection of electrolytic ones. Can I use those instead?