Help understanding isolated ground

[Dmeads]

Okay I am looking at gate drivers for mosfets and some have an isolated ground. Can you tie this to regular ground at it will be okay for does it have to be a separate ground. How does one do this with power supplies that are tied together through mains ground?

[David Hess]

The isolated ground can be tied to anything including the other ground.

[Al3579]

Isolated ground can be connected to ground but it creates a ground loop.
Ever wonder why hospitals and audio people use isolation transformers and isolated ground outlets. If you care about your signal integrity you don't connect it to chassis ground.
You have signal ground then you have chassis ground which is there for protection not so you can use it as a big electrical buss.
Neutral and ground should only be connected at one point usually the main panel in your house.  Now what you do with that differential input is put it any where you need it except for the chassis ground. Now the isolated ground is there because you might be getting a signal from something that might have a different signal reference or chassis reference if they connected it to ground.

Signal ground and chassis ground aren't the same thing.

[David Hess]

Isolated ground can be connected to ground but it creates a ground loop.

Some other part of the circuit might create a ground loop but the isolated ground itself will not.

Sometimes isolation amplifiers are used for exactly this purpose; each ground of the isolation amplifier is connected to different points of the same ground to remove the common mode voltage between those points.

[Siwastaja]

No, no, no.

The first step is to completely get rid of words "isolated" and "ground", thinking they have some generic value or typical implications. A sentence like "Isolated ground can be connected to ground but it creates a ground loop" is a good example - it's completely void of any meaning whatsoever, and of course, if you try to force any meaning to it, it's just wrong.

Instead, draw an actual circuit diagram of the actual system and look where the currents will flow, based on basic Kirchhoff laws. Draw your "ground" connections and look if you can make your desired currents flow, or if undesired currents will flow.

You can use basic circuit simulators to verify your thoughts.

Isolated simply means there is no electrical connection, and hence no current can flow.

"Ground" simply can mean anything, really. It's an arbitrary convenience "tag" in electronics, similar to a "reference level". Multiple grounds may exist, or may not. Whether they can be connected together is a similar question to whether wires xyz and asdf could or should be connected together. You only know by understanding the circuit.

As for the isolated gate driver, they have the isolation for a reason, and it costs money. You should understand where you are going to connect it and why. Otherwise, you are likely to create high-current short circuits.

[iMo]

Grounds..