Electronics > Beginners
Talk me through this simple circuit?
vk6zgo:
But wait!---- There's more!
Back in the day, there were two schools of thought on grounding.
One, which I might call "The British way", drew schematics with a lne at the bottom normally called the "earth rail" (Another term for what others called "ground") & one at the top called the "supply rail".
The top one was usually the positive side of the supply, & the bottom one was usually the negative side of the supply.(not always, though, as with early PNP transistor circuits, the connections were reversed)
The supply side of each circuit component ultimately was connected to the top "rail" & the ground side to the bottom "rail".
This showed clearly where all the "ground" points were connected together, but was a bit unwieldy.
The other school of thought was what I might call "The American way",
With this method, the "ground" was indicated by a special symbol, which meant that all points which had this symbol were connected
Just to show that they weren't complete "party poopers" the Americans often drew simpler schematics in the British style.
European schematics were usually "somewhere in between".
Ultimately, the "American way" won out, as, with the advent of multiple supply rails, the other way became very messy to implement.
Unfortunately for "noobs", it doesn't "lay it on the line" as to how ground connections work, like the old "British way" did.
Nerull:
--- Quote from: Mr D on June 01, 2019, 08:05:03 am ---Let's take it back to the original circuit in the first post of this thread.
Let's put aside rstofer's comments about the efficacy of this circuit, i presume it at least works to some degree.
Let's place this circuit on it's own in intergalactic deep space and turn it on.
Now, this circuit contains 6 connections to ground.
My question is simply this: if we cut all those connections to ground, will the circuit still work in exactly the same way?
If not, why not? Could someone give me one or two example of why the components in the circuit won't do what they're expected to do without these ground connections?
--- End quote ---
"Ground" in a circuit without any actual earth-ground connections is just a shorthand. It represents an invisible wire connecting all the 'ground' points together, just as if you have multiple power nodes named 'Vcc' you would assume they are connected.
This is the exact same circuit, drawn two different ways:
We have chosen, by convention, to call the common return path in DC circuits "Ground", regardless of whether it has any real connection to earth ground. It really doesn't mean anything more. It seems like you are vastly overthinking this.
DimitriP:
--- Quote ---This is the exact same circuit, drawn two different ways:
--- End quote ---
But ...you can only simulate one of the two. The one on the left.
Mr D:
I don't agree i'm overthinking it, i'm simply trying to get a clear picture of what is actually meant by the ground symbol in a circuit schematic!
You mentioned the "return path", this is the first time anyone has called it that in this thread and that makes things a bit clearer.
I think part of my confusion is that there are two things under the umbrella term of "ground", and they seem (to me) totally unrelated.
Firstly you have the safety issues and the connection (for whatever reason) with the real ground, chassis or whatever.....
Secondly you have this return path, whose purpose is sometimes to close the circuit (although not in my circuit example in this thread) and give you a short cut route for any component in the circuit to a common point of lowest potential, typically just before the negative terminal, or if you're using a rail splitter, to that point in between the two resistors.
So in this usage, the word "ground" could be substituted with "return path".
And if we were only talking about circuits in intergalactic space, the term "ground" would be a meaningless and confusing obfuscation.
Once these circuits are returned in a spaceship to planet earth, we could happily continue using the "return path" nomenclature, adding, when necessary, "this point needs to be connected to the chassis or real ground or whatever".
So could someone look at the circuit in the first post and choose one of those connections to ground (apart from the rail splitter connection) and explain why, at that point, the designer said to himself "right, here we need to connect to the return path"? (he probably thought of it as "ground" :P)
timelessbeing:
In the amplifier circuit, the ground is connected to the chassis.
Also note, "return path" implies negative polarity, which is not always the common or ground node. For example, on old cars, the chassis and engine block were connected to battery positive. In that case the chassis acts as source rather than return.
Also, note that "return path" doesn't make sense in AC circuits, where current reverses direction in each cycle. In differential circuits, you have positive and negative signals which are referenced to neutral which is grounded.
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