0V in a schematic

[Eeyore]

Rich wrote:

I can see that when you see a voltage statement on a schematic, that is a
statement of the voltage at that point with reference to some other point in
the schematic. It's not saying necessarily that the stated voltage is across
the component.

Okay, is 0V on a schematic meant to be zero volts above ground potential, or
can it be any arbitary voltage above ground potential? Is it an absolute
statement that the point is at zero volts with reference to ground?

Are you really sure you're cut out for electronics ?

Graham

 

[Eeyore]

Nobody wrote:

On Sun, 08 Feb 2009 12:42:42 +0000, Rich wrote:

If I have two equal resistances in a voltage divider, is there any special
significance to the tapping point (in between the two resistors) as a
voltage refrence?

Is it ever considered to be a "natural" 0V point, or GND? Could you ever
call that point a virtual ground? Or is the virtual groubnd concept
something entirely different?

"virtual ground" normally refers to a point which is maintained at
ground potential by feedback, e.g. the inverting input of an op-amp whose
non-inverting input is tied to ground.

But it may not be so simple.

Graham

 

[ian field]

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:4991FDAA.B3CC16E5@hotmail.com...

Nobody wrote:

On Sun, 08 Feb 2009 12:42:42 +0000, Rich wrote:

If I have two equal resistances in a voltage divider, is there any
special
significance to the tapping point (in between the two resistors) as a
voltage refrence?

Is it ever considered to be a "natural" 0V point, or GND? Could you
ever
call that point a virtual ground? Or is the virtual groubnd concept
something entirely different?

"virtual ground" normally refers to a point which is maintained at
ground potential by feedback, e.g. the inverting input of an op-amp whose
non-inverting input is tied to ground.

But it may not be so simple.

Graham

A fun situation is the reference point of a mains powered SMPSU, usually
being the negative end of the bridge rectifier - makes quite a loud "pop" if
you accidentally ground it!

 

[John Fields]

On Tue, 10 Feb 2009 22:19:27 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

Rich wrote:

I can see that when you see a voltage statement on a schematic, that is a
statement of the voltage at that point with reference to some other point in
the schematic. It's not saying necessarily that the stated voltage is across
the component.

Okay, is 0V on a schematic meant to be zero volts above ground potential, or
can it be any arbitary voltage above ground potential? Is it an absolute
statement that the point is at zero volts with reference to ground?

Are you really sure you're cut out for electronics ?

---
Fuck you, Graham.

At least he's laying it all out so that we can see what he understands
and where he's weak so that those of us who care can help him along on
his way to enlightenment.

And you?

Instead of helping, you try to make him feel bad about himself by
insulting him.

Why would you do that?

JF

 

[John Fields]

On Tue, 10 Feb 2009 22:20:26 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

Nobody wrote:

On Sun, 08 Feb 2009 12:42:42 +0000, Rich wrote:

If I have two equal resistances in a voltage divider, is there any special
significance to the tapping point (in between the two resistors) as a
voltage refrence?

Is it ever considered to be a "natural" 0V point, or GND? Could you ever
call that point a virtual ground? Or is the virtual groubnd concept
something entirely different?

"virtual ground" normally refers to a point which is maintained at
ground potential by feedback, e.g. the inverting input of an op-amp whose
non-inverting input is tied to ground.

But it may not be so simple.

---
So explain why not...

JF

 

[Jamie]

John Fields wrote:

On Tue, 10 Feb 2009 22:19:27 +0000, Eeyore
rabbitsfriendsandrelations@hotmail.com> wrote:



Rich wrote:


I can see that when you see a voltage statement on a schematic, that is a
statement of the voltage at that point with reference to some other point in
the schematic. It's not saying necessarily that the stated voltage is across
the component.

Okay, is 0V on a schematic meant to be zero volts above ground potential, or
can it be any arbitary voltage above ground potential? Is it an absolute
statement that the point is at zero volts with reference to ground?

Are you really sure you're cut out for electronics ?


---
Fuck you, Graham.

At least he's laying it all out so that we can see what he understands
and where he's weak so that those of us who care can help him along on
his way to enlightenment.

And you?

Instead of helping, you try to make him feel bad about himself by
insulting him.

Why would you do that?

Because he's ignorant? Which comes in various colors btw.

http://webpages.charter.net/jamie_5"

 

[Jamie]

Rich wrote:

"krw" <krw@att.bizzzzzzzzzzz> wrote in message
news:nak1p45tgkbapiofvtch6d9pboc3rv8r8v@4ax.com...

On Mon, 9 Feb 2009 14:16:43 -0000, "Rich" <notty@emailo.com> wrote:


"Rich" <notty@emailo.com> wrote in message
news:6vamfpFj27vcU1@mid.individual.net...

Pretty stiff opamp, too, since to drive the virtual ground to 0V will
require 2A out of the opamp.

JF


Yes, I later realised the math was wrong. I keep switching between
inverting
amplifier and non inverting amplifier. I should concentrate on each
type
of
circuit individually.

That diagram I drew was to show *to myself*, how in principle we
obtain a
virtual ground at V- for the inverting amplifier. And why we get
Vout as
we
do for a given combination of Rin and Rf.

I never knew what virtual ground was until now. And now I know, that as
long
as one end of a circuit compont is held at 0V with reference to
ground by
an
"opposing voltage", for all intents and purposes it's akin to being
connected to GND, or 0v. As long as there is somewhere for the
current to
flow.


I mean, current must find it's way back to the source, so, to the
source, it
looks like it's terminated in Rin.

V- must be 0V above grund or it would look to the source as if it was
terminated in a different resistance value than Rin. If for instance
Vin was
10V, and Rin was 10K, and V- was at a potential of 5V above ground, the
voltage across Rin would be 5V, not 10V. So the source would see an
input
resistance of 20K, because current flowing in Rin would be 5V/10K =
0.5mA.,
whereas it ought to be 1mA. I think I'm getting it. :c)


No, if I understand the above, the input impedance is still Rin since
the '-' input is still a voltage source. It's no longer "ground", but
ground is just what *you* choose to call ground.


Well, what I'm saying is that the input source is connected to GND, or a
point that we call 0V. The source is connected to one side of Rin. It's
essential that the other side of Rin is either connected to GND, or 0V
for the source to see it's being connected across Rin. With a virtual
ground arrangement, if the "earthy" one side of Rin got to be at 5V,
then source will not see Rin, but some other terminating value. That's
what I understand.

0 volts found in a circuit normally indicates the circuit's common
"COM" reference point to all other nodes of that circuit. It does not
mean how ever, that it would be a common to a remote circuit. when I
say remote, I refer to a device that allows external connection from
some other devices.

Hence, the 0V ref is a point to where all other nodes in that circuit
are in common with it.

Keep in mind that the "Common" supplied, for external/remote
connection does not have to be this same 0V ref, It could be a virtual
ground derived from this circuit or an isolated unit.

0V ref normally indicates a point of reference (com) for that circuit
and does not necessarily mean it's the global common.


And to confuse things more, a Virtual ground could also be the 0V ref
which would also be the common through out. This is normally found where
only a single stand alone rail supply is available, for example, a
battery or xformer with only 1 rail output. Both would offer isolation
from ground conflicts when connecting to external "common" sources, but
offer a way of creating a dual rail scenario to generate signals of +/-
with respect to ground/common.

assuming the (+)&(-) is from a single battery or Single rail isolated
supply.


(+)-------[1k]-------(V-Grnd/0V Ref)-------[1k]--------(-)



The above VG could be used as a common in an op-amp circuit while
the (+) and (-) terminals of our isolated single rail supply creates
the (+) and (-) rails with respect to the VG (virtual Ground) for the
Op-amp's Vcc and Vee supply terminals.


The resulting output of the op-amp could generate a true
+/- signal.

The only limitations of a VG, you need twice the voltage to obtain
the dual rail voltages..

12 Battery would yield 6V +/- for example minus the losses from other
things, we'll not get into.

http://webpages.charter.net/jamie_5"