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'[EE] grounding problem'
2008\07\11@101445 by gardenyu

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Refer to the attached figure, (application for UC2843B in flyback converter design), it includes AC input, rectifier, a primary winding of a transformer and a current-controlled FET at low side    If we look at the full-bridge rectifier side, you can see a ground there (no matter circuit ground or earth ground). It makes sense, right? For a similar design I saw, they didn't connect that lead to any ground, but just use one high side as power and the other lower voltage side as a "fake ground", and even the chip use that "fake ground". Do you have any idea on what problem might happen to the chip or anything else? If there is AC surge or anything else?
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2008\07\11@114539 by Alan B. Pearce

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>Refer to the attached figure, (application for UC2843B in flyback converter
>design),

The ground they show there will be a purely circuit ground within the
schematic as presented.

DO NOT connect this to mains ground, as there will be a 'Big Bang (TM)'



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2008\07\11@132256 by gardenyu

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 Yes, the attached schematic works and is reasonable.  but another similar design does not have this ground at all. The circuit just survives between a higher voltage and a lower one, which is floated.I wonder if the chip can have a ground reference which is not pure ground.
The latter one also works, but is there any potential problem because of this?



> From: spam_OUTA.B.PearceTakeThisOuTspamrl.ac.uk> To: .....piclistKILLspamspam@spam@mit.edu> Subject: Re: [EE] grounding problem> Date: Fri, 11 Jul 2008 16:45:03 +0100> > >Refer to the attached figure, (application for UC2843B in flyback converter > >design),> > The ground they show there will be a purely circuit ground within the > schematic as presented.> > DO NOT connect this to mains ground, as there will be a 'Big Bang (TM)'> _________________________________________________________________
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2008\07\11@134011 by Geo

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On 11 Jul 2008, at 17:22, gardenyu wrote:

> Yes, the attached schematic works and is reasonable.

No - it will go bang if you connect a diode from line to earth.
The earth symbol is incorrectly used in your example.
 
> but another similar design does not have this ground at all. The circuit just survives between a higher voltage and a lower one, which is floated.I wonder if the chip can have a ground reference which is not pure ground.

A circuit only needs to be a contionous to work. Ground is irrelevant. Think
flashlight.

George Smith

2008\07\12@060349 by Vasile Surducan

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On 7/11/08, Geo <lintechspamKILLspamblueyonder.co.uk> wrote:
> On 11 Jul 2008, at 17:22, gardenyu wrote:
>
> > Yes, the attached schematic works and is reasonable.
>
> No - it will go bang if you connect a diode from line to earth.

That's not "earth" nor 'neutral". Is just a symbol representing the
ground of the circuit (where ground = reference for measured
voltages).


> The earth symbol is incorrectly used in your example.
>
> > but another similar design does not have this ground at all. The circuit just survives between a higher voltage and a lower one, which is floated.I wonder if the chip can have a ground reference which is not pure ground.
>
> A circuit only needs to be a contionous to work. Ground is irrelevant. Think
> flashlight.
>
> George Smith
>
> -

2008\07\12@070134 by John La Rooy

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There are different symbols for the different types of ground.
The one with the three horizontal lines is earth

http://en.wikipedia.org/wiki/Ground_(electricity)#Electronics

2008\07\12@083907 by Geo

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On 12 Jul 2008, at 3:03, Vasile Surducan wrote:

> That's not "earth" nor 'neutral". Is just a symbol representing the
> ground of the circuit (where ground = reference for measured
> voltages).
>
No it is The Earth.
see for example:-
www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/earth/earth.htm
or  - if line wraps use:-
http://tinyurl.com/5fhmmy



George Smith

2008\07\12@142247 by Vasile Surducan

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On 7/12/08, Geo <.....lintechKILLspamspam.....blueyonder.co.uk> wrote:
> On 12 Jul 2008, at 3:03, Vasile Surducan wrote:
>
> > That's not "earth" nor 'neutral". Is just a symbol representing the
> > ground of the circuit (where ground = reference for measured
> > voltages).
> >
> No it is The Earth.
> see for example:-
> www.st-andrews.ac.uk/~www_pa/Scots_Guide/info/earth/earth.htm
> or  - if line wraps use:-
> http://tinyurl.com/5fhmmy

Guys, read deep into the schematic and think twice everytime you are
reading it. The symbol must not be taken as you have been teached at
school without thinking.
Those three neurons (two from the brain and one from the pants) must
be put at work...
:)

2008\07\12@194602 by peter green

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John La Rooy wrote:
> There are different symbols for the different types of ground.
> The one with the three horizontal lines is earth
>
> http://en.wikipedia.org/wiki/Ground_(electricity)#Electronics
>  
That may be some standard for which to use when, but the reality is that
the majority of circuit diagrams I see use the "earch ground" symbol
regardless of whether thier ground rail is actually connected to earth.



2008\07\12@222120 by Forrest W. Christian

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I think there's two issues here...

1)  There is a standard for the symbols for the three types of ground...
earth  (line with bars), Chassis (pitchfork), and circuit (upside down
triangle - or arrow pointing down).   These should be used appropriately
but many do not use these correctly at all - and in many situations it
doesn't really matter.    For most pic circuits, whether or not it is
earth, chassis and/or circuit ground is irrelevant, as long as
everything which needs to be tied electrically together is tied
electrically together.     Because of this many use these symbols
interchangeably, even though they are not technically the same.   So
when reading a circuit, you need to think about which ground is *really*
meant, and not blindly assume the symbols are used correctly.

2) The shown circuit is drawn in a very dangerous way.   It uses the
earth ground symbol instead of circuit ground.   It's dangerous because
it does so in a circuit where interconnecting circuit ground and earth
ground would result in a dangerous situation, since the most common
source of 115VAC (at least in the states) has one leg attached to earth
ground.  What shocks me is that this schematic appears to be  from the
official onsemi datasheet.   It makes me trust onsemi less, since this
is potentially a very bad error.   Makes you wonder what other but less
obvious dangerous errors exist in other  (sort of the Brown M&M effect).

-forrest

Vasile Surducan wrote:
{Quote hidden}

2008\07\12@232719 by Jinx

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> 1)  There is a standard for the symbols for the three types of ground

Yes, and to mean anything, anyone who draws schematics should
adhere to them. For example, on the primary side of a transformer
use the chassis earth symbol, on the secondary use the signal/ground
symbol and indicate whether it/they should be joined to chassis

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