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design | Transformer dot notation


There are 11 messages in this thread.

You are currently looking at messages 1 to 10.

Transformer dot notation - reggie - 2008-06-11 15:04:00

Hi all,

I have just been reviewing some magnetic stuff and come across some
discrepancies in dot notation between different documents.

I have sketched out a diagram as it is probably too hard to describe,
it’s a small JPG file so don’t worry there are no virus issues in
downloading this file.

http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6e747d7fa93d0fcaf3c71e8dd.html

Fig1 and fig 2 are the same electrically but I have just moved the
secondary round the core to see it in my minds eye.

What I am confused about is fig4s current direction in relation to the
dots (I know its open circuit but assume it’s terminated) compared to
the forward converter (fig5)

I reckon the transformer is the same and connected in the same way, if
this is the case then why when the current moves from 1 to 2 on both
figures 4&5 primary’s, does the current in the forward converters
secondary move in the opposite direction from that of the standard
transformer?

I know current can only flow from pin 4 to pin3 in the forward
converter due to the top diode blocking current flow in the opposite
direction. I also know that pin 3 will be positive and thus forward
bias the top diode, what is really bothering me is  the secondary
current direction found in multiple textbooks describing transformers.

I was wondering if there was some good information on the web about
dot notation relating to transformer physical construction, or can
someone please explain the discrepancies between current directions.
(I am assuming conventional current flow from +ve to -ve).

I know its basic, but its something I want to clear up,

Thanks,

Reggie.



Re: Transformer dot notation - Joel Koltner - 2008-06-11 16:13:00

"reggie" <v...@googlemail.com> wrote in message 
news:0...@m73g2000hsh.googlegroups.com...
"Fig1 and fig 2 are the same electrically but I have just moved the
secondary round the core to see it in my minds eye.

What I am confused about is fig4s current direction in relation to the
dots (I know its open circuit but assume it’s terminated) compared to
the forward converter (fig5)"

OK.  You have the dots drawn correctly.

"I reckon the transformer is the same and connected in the same way, if
this is the case then why when the current moves from 1 to 2 on both
figures 4&5 primary’s, does the current in the forward converters
secondary move in the opposite direction from that of the standard
transformer?"

The dot convention tells you where a positive voltage will "show up" when you 
feed positive voltage in on another winding with the dot being the positive 
end.  It also tells you that flux will be produced in the core in the same 
direction *if* you were to *feed* current into that end of the winding. 
*However*, what "normally" happens is that you *provide* a voltage on one coil 
(the primary) -- hence creating flux in one direction --, the voltage appears 
in phase at the other winding and (if you connect a load) current flows *out* 
of the other winding (the secondary) *thus producing flux OPPOSITE to that 
produced by the primary!*  The goal in building a perfect transformer is to 
get these fluxes to completely *cancel*, so that a load gets "reflected" from 
the secondary back to the primary with nothing more than a "turns ratio 
square" multiplier.

In figure 4, (assuming Ip and Is are positive currents), both the primary and 
secondary are creating flux in the transformer in the *same* direction -- each 
winding will "see" the other winding as simply another generator (voltage 
source), and potentially try to fight one another if the applied voltages are 
out of phase.   (Think about how transformers meant for either 120V or 240V 
have their primaries wound: Either in series or in parallel, but such that the 
current enters the windings to create flux in the same direction.  This is 
essentially what you're drawn in figure 4: Two windings meant to be *driven* 
in parallel.)

The confusion here might stem from the fact that the transformer itself 
doesn't care which way current flows through the windings -- with the 
appropriate sources, you can force current to flow either way through any 
winding; all the transformer does is to take whatever currents are flowing in 
the windings and create flux internally.  (Faraday's law then tells you what 
voltages to expect for those un-driven windings where you didn't already know 
it!)  Since there's a fixed *voltage* ratio between the windings, if you 
connect a *load* to a winding, the turns ratio and the load then determine the 
current direction as well.  (...which, again, will always so as to *oppose* 
the flux generate by the primary.)

"what is really bothering me is  the secondary
current direction found in multiple textbooks describing transformers."

What they're descrbing is meant to tell you how to determine the dot 
convention: Using the right-hand rule, force current through a given winding, 
and see which way the resultant flux points.  In your forward converter, 
what's going on is "transformer action," wherein a load at one winding will 
have current flow through it in such a way as to *oppose the flux generated by 
another winding*.

Does this help any?

---Joel



Re: Transformer dot notation - Guy Macon - 2008-06-11 16:14:00

Content-Transfer-Encoding: 8Bit


reggie wrote:

>I have just been reviewing some magnetic stuff and come across some
>discrepancies in dot notation between different documents.
>
>I have sketched out a diagram as it is probably too hard to describe,
>it’s a small JPG file so don’t worry there are no virus issues in
>downloading this file.
>
>http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6e747d7fa93d0fcaf3c71e8dd.html
>
>Fig1 and fig 2 are the same electrically but I have just moved the
>secondary round the core to see it in my minds eye.

Yes.  And Figure 3 is the same electrically but you have
just used fewer turns.

>What I am confused about is fig4s current direction in relation to the
>dots (I know its open circuit but assume it’s terminated) compared to
>the forward converter (fig5)

>I reckon the transformer is the same and connected in the same way, if
>this is the case then why when the current moves from 1 to 2 on both
>figures 4&5 primary’s, does the current in the forward converters
>secondary move in the opposite direction from that of the standard
>transformer?

>what is really bothering me is  the secondary current direction 
>found in multiple textbooks describing transformers.
>
>I was wondering if there was some good information on the web about
>dot notation relating to transformer physical construction, or can
>someone please explain the discrepancies between current directions.
>(I am assuming conventional current flow from +ve to -ve).
>
>I know its basic, but its something I want to clear up,

The schematic representations in figures 4 and 5 are not pictures 
of the physical core/winding layout, and more than the schematic 
representation of a resistor implies some kind of zigzag inside
or the schematic representation of a capacitor implies two plates
instead of dozens of interleaved plates.  You could renumber the 
terminals or move the dot to the bottom and it the same basic 
schematic symbol would describe a a different physical core/winding 
layout.  That's why we call them "symbols."  

-- 
Guy Macon
<http://www.guymacon.com/>


Re: Transformer dot notation - James Arthur - 2008-06-11 16:21:00

reggie wrote:
> Hi all,
> 
> I have just been reviewing some magnetic stuff and come across some
> discrepancies in dot notation between different documents.
> 
> I have sketched out a diagram as it is probably too hard to describe,
> it’s a small JPG file so don’t worry there are no virus issues in
> downloading this file.
> 
> http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6e747d7fa93d0fcaf3c71e8dd.html
> 
> Fig1 and fig 2 are the same electrically but I have just moved the
> secondary round the core to see it in my minds eye.
> 
> What I am confused about is fig4s current direction in relation to the
> dots (I know its open circuit but assume it’s terminated) compared to
> the forward converter (fig5)
> 
> I reckon the transformer is the same and connected in the same way, if
> this is the case then why when the current moves from 1 to 2 on both
> figures 4&5 primary’s, does the current in the forward converters
> secondary move in the opposite direction from that of the standard
> transformer?
> 
> I know current can only flow from pin 4 to pin3 in the forward
> converter due to the top diode blocking current flow in the opposite
> direction. I also know that pin 3 will be positive and thus forward
> bias the top diode, what is really bothering me is  the secondary
> current direction found in multiple textbooks describing transformers.
> 
> I was wondering if there was some good information on the web about
> dot notation relating to transformer physical construction, or can
> someone please explain the discrepancies between current directions.
> (I am assuming conventional current flow from +ve to -ve).
> 
> I know its basic, but its something I want to clear up,
> 
> Thanks,
> 
> Reggie.

That's a lot of words, a splash ad site, and a mystery
download.

A simple question would get more replies.  An ASCII
drawing would be even better.

Here's a diagram to help you along (fill in the details):

                 T1       D1
   Vcc>--------.     .----|>|---+----> Vout
              o ) || ( o        |
                ) || (         C1
                ) || (          |
                ) || (         ==           .---'      '---.    GND
     Q1    |              |
         |/              ==     ----|               GND
         |>.
           |
           |
          ==          GND

Cheers,
James Arthur

Re: Transformer dot notation - Bob Eld - 2008-06-12 00:59:00

"reggie" <v...@googlemail.com> wrote in message
news:0...@m73g2000hsh.googlegroups.com...
Hi all,

I have just been reviewing some magnetic stuff and come across some
discrepancies in dot notation between different documents.

I have sketched out a diagram as it is probably too hard to describe,
it’s a small JPG file so don’t worry there are no virus issues in
downloading this file.

http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6e747d7f
a93d0fcaf3c71e8dd.html

Fig1 and fig 2 are the same electrically but I have just moved the
secondary round the core to see it in my minds eye.

What I am confused about is fig4s current direction in relation to the
dots (I know its open circuit but assume it’s terminated) compared to
the forward converter (fig5)

I reckon the transformer is the same and connected in the same way, if
this is the case then why when the current moves from 1 to 2 on both
figures 4&5 primary’s, does the current in the forward converters
secondary move in the opposite direction from that of the standard
transformer?

I know current can only flow from pin 4 to pin3 in the forward
converter due to the top diode blocking current flow in the opposite
direction. I also know that pin 3 will be positive and thus forward
bias the top diode, what is really bothering me is  the secondary
current direction found in multiple textbooks describing transformers.

I was wondering if there was some good information on the web about
dot notation relating to transformer physical construction, or can
someone please explain the discrepancies between current directions.
(I am assuming conventional current flow from +ve to -ve).

I know its basic, but its something I want to clear up,

Thanks,

Reggie.

The dots on a transformer drawing usually indicate the start or beginnings
of the windings. They could also indicate the end of the windings. The point
is that all windings are dotted the same. All starts or all ends on a given
transformer. They are not mixed.

This means that the instantaneous polarity is the same on all dots. If the
polarity of the primary dot is driven positive, all other winding dots are
also positive in the same instant.

If current is flowing into a primary dot it must flow out of all other dots
(secondaries). Likewise if current is flowing out of a primary dot it must
flow into all other dots. The primary is the sink of current and the
secondaries are the source of current.









Re: Transformer dot notation - Tim Williams - 2008-06-12 01:30:00

"James Arthur" <b...@verizon.net> wrote in message 
news:GtW3k.46590$bs3.22826@trnddc07...
>> http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6e747d7fa93d0fcaf3c71e8dd.html
>
> That's a lot of words, a splash ad site, and a mystery
> download.

Mystery?  It's a JPG, like the man said.  I'm viewing it in L-View Pro right 
now.  I'm supposing you did too...

> Here's a diagram to help you along (fill in the details):
>
>                 T1       D1
>   Vcc>--------.     .----|>|---+----> Vout
>              o ) || ( o        |
>                ) || (         C1
>                ) || (          |
>                ) || (         ==>           .---'      '---.    GND
>     Q1    |              |
>         |/              ==>     ----|               GND
>         |>.
>           |
>           |
>          ==>          GND

The transformer is backwards for such a flyback converter.  But that doesn't 
matter, because he drew a forward converter, which uses two diodes and a 
choke (except for the cheapass / ignorant "engineers" that do them without 
chokes... eugh...).

Tim

-- 
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms 



Re: Transformer dot notation - reggie - 2008-06-12 16:57:00

On 12 Jun, 06:30, "Tim Williams" <tmoran...@charter.net> wrote:
> "James Arthur" <bogusabd...@verizon.net> wrote in message
>
> news:GtW3k.46590$bs3.22826@trnddc07...
>
> >>http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6...
>
> > That's a lot of words, a splash ad site, and a mystery
> > download.
>
> Mystery?  It's a JPG, like the man said.  I'm viewing it in L-View Pro right
> now.  I'm supposing you did too...
>
>
>
>
>
> > Here's a diagram to help you along (fill in the details):
>
> >                 T1       D1
> >   Vcc>--------.     .----|>|---+----> Vout
> >              o ) || ( o        |
> >                ) || (         C1
> >                ) || (          |
> >                ) || (         ===
> >           .---'      '---.    GND
> >     Q1    |              |
> >         |/              ===
> >     ----|               GND
> >         |>.
> >           |
> >           |
> >          ===
> >          GND
>
> The transformer is backwards for such a flyback converter.  But that doesn't
> matter, because he drew a forward converter, which uses two diodes and a
> choke (except for the cheapass / ignorant "engineers" that do them without
> chokes... eugh...).
>
> Tim
>
> --
> Deep Friar: a very philosophical monk.
> Website:http://webpages.charter.net/dawill/tmoranwms- Hide quoted text -
>
> - Show quoted text -

Guy, I think you have miss understood what I was asking, probably my
long winded explanation… Sorry…

Joel thanks,

Your reply made sense to me. I hadn’t thought of the possibility of
two drive circuits like a split primary mains transformer.  I thought
I’d always understood dot notation until I came across some lecture
notes from MIT (Massachusetts institute of technology) where the
current directions didn’t make sense when applied to forward or fly
back circuits.

I last studied magnetic’s back in the early 90s, so just wanted to be
sure I wasn’t loosing my mind!!

Your response was very helpful, thanks again!

James,

I take your point about downloading “mystery files” But as Tim said it
was a JPG so no virus issues. Sorry for being critical but you looked
at it and I have managed to get a good answer; so I shall not be
restricting myself to ASCII drawings in the future!

Engineers like diagrams! Why not move with technology, throw caution
to the wind and give a video clip in future! Engineers communicate in
diagrams so why not on line?

Bob, I agree with what you have said, thanks!

Thanks all again,

Reggie.




Re: Transformer dot notation - James Arthur - 2008-06-12 17:41:00

Tim Williams wrote:
> "James Arthur" <b...@verizon.net> wrote in message 
> news:GtW3k.46590$bs3.22826@trnddc07...
>>> http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6e747d7fa93d0fcaf3c71e8dd.html
>> That's a lot of words, a splash ad site, and a mystery
>> download.
> 
> Mystery?  It's a JPG, like the man said.  I'm viewing it in L-View Pro right 
> now.  I'm supposing you did too...

Nope.  I saw a bunch of ads & didn't care to click any further.

A courteous stranger ought not require of us our trust and
inconvenience in addition to our advice. Besides, ASCII art means
these things get archived, for future seekers.


>> Here's a diagram to help you along (fill in the details):
>>
>>                 T1       D1
>>   Vcc>--------.     .----|>|---+----> Vout
>>              o ) || ( o        |
>>                ) || (         C1
>>                ) || (          |
>>                ) || (         ==>>           .---'      '---.    GND
>>     Q1    |              |
>>         |/              ==>>     ----|               GND
>>         |>.
>>           |
>>           |
>>          ==>>          GND
> 
> The transformer is backwards for such a flyback converter.  But that doesn't 
> matter, because he drew a forward converter, which uses two diodes and a 
> choke (except for the cheapass / ignorant "engineers" that do them without 
> chokes... eugh...).
> 
> Tim

Umm, that's a forward converter, which is what the OP meandered on about.

True, it could use a catch diode and an extra inductor if the OP really 
meant "forward converter," but I wasn't sure.

Since description was lacking, I offered a compromise meant as a 
starting point--one which would adapt easily to suit either case--and a 
gentle intro to ASCII art in the bargain. "Fill in the details" was 
supposed to encourage the OP to modify it to his purpose.

Cheers,
James Arthur

Re: Transformer dot notation - James Arthur - 2008-06-12 18:27:00

reggie wrote:
> On 12 Jun, 06:30, "Tim Williams" <tmoran...@charter.net> wrote:
>> "James Arthur" <bogusabd...@verizon.net> wrote in message
>>
>> news:GtW3k.46590$bs3.22826@trnddc07...
>>
>>>> http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6...
>>> That's a lot of words, a splash ad site, and a mystery
>>> download.
>> Mystery?  It's a JPG, like the man said.  I'm viewing it in L-View Pro right
>> now.  I'm supposing you did too...
>>
>>
>>
>>
>>
>>> Here's a diagram to help you along (fill in the details):
>>>                 T1       D1
>>>   Vcc>--------.     .----|>|---+----> Vout
>>>              o ) || ( o        |
>>>                ) || (         C1
>>>                ) || (          |
>>>                ) || (         ==>>>           .---'      '---.    GND
>>>     Q1    |              |
>>>         |/              ==>>>     ----|               GND
>>>         |>.
>>>           |
>>>           |
>>>          ==>>>          GND
>> The transformer is backwards for such a flyback converter.  But that doesn't
>> matter, because he drew a forward converter, which uses two diodes and a
>> choke (except for the cheapass / ignorant "engineers" that do them without
>> chokes... eugh...).
>>
>> Tim
>>
>> --
>> Deep Friar: a very philosophical monk.
>> Website:http://webpages.charter.net/dawill/tmoranwms- Hide quoted text -
>>
>> - Show quoted text -
> 
> Guy, I think you have miss understood what I was asking, probably my
> long winded explanation… Sorry…
> 
> Joel thanks,
> 
> Your reply made sense to me. I hadn’t thought of the possibility of
> two drive circuits like a split primary mains transformer.  I thought
> I’d always understood dot notation until I came across some lecture
> notes from MIT (Massachusetts institute of technology) where the
> current directions didn’t make sense when applied to forward or fly
> back circuits.
> 
> I last studied magnetic’s back in the early 90s, so just wanted to be
> sure I wasn’t loosing my mind!!
> 
> Your response was very helpful, thanks again!
> 
> James,
> 
> I take your point about downloading “mystery files” But as Tim said it
> was a JPG so no virus issues. Sorry for being critical but you looked
> at it and I have managed to get a good answer; so I shall not be
> restricting myself to ASCII drawings in the future!

Sure, we like diagrams, no question about that.  I did not download or 
view yours, but I'm glad you got the answers you wanted from others who did.

> Engineers like diagrams! Why not move with technology, throw caution
> to the wind and give a video clip in future! Engineers communicate in
> diagrams so why not on line?

Personally, I prefer pencil and paper.

Cheers,
James Arthur

Re: Transformer dot notation - reggie - 2008-06-13 04:24:00

On 12 Jun, 23:27, James Arthur <bogusabd...@verizon.net> wrote:
> reggie wrote:
> > On 12 Jun, 06:30, "Tim Williams" <tmoran...@charter.net> wrote:
> >> "James Arthur" <bogusabd...@verizon.net> wrote in message
>
> >>news:GtW3k.46590$bs3.22826@trnddc07...
>
> >>>>http://www.adrive.com/public/5040381aef1a269de9465a441db0e5f92b0d4fc6...
> >>> That's a lot of words, a splash ad site, and a mystery
> >>> download.
> >> Mystery?  It's a JPG, like the man said.  I'm viewing it in L-View Pro right
> >> now.  I'm supposing you did too...
>
> >>> Here's a diagram to help you along (fill in the details):
> >>>                 T1       D1
> >>>   Vcc>--------.     .----|>|---+----> Vout
> >>>              o ) || ( o        |
> >>>                ) || (         C1
> >>>                ) || (          |
> >>>                ) || (         ===
> >>>           .---'      '---.    GND
> >>>     Q1    |              |
> >>>         |/              ===
> >>>     ----|               GND
> >>>         |>.
> >>>           |
> >>>           |
> >>>          ===
> >>>          GND
> >> The transformer is backwards for such a flyback converter.  But that doesn't
> >> matter, because he drew a forward converter, which uses two diodes and a
> >> choke (except for the cheapass / ignorant "engineers" that do them without
> >> chokes... eugh...).
>
> >> Tim
>
> >> --
> >> Deep Friar: a very philosophical monk.
> >> Website:http://webpages.charter.net/dawill/tmoranwms-Hide quoted text -
>
> >> - Show quoted text -
>
> > Guy, I think you have miss understood what I was asking, probably my
> > long winded explanation… Sorry…
>
> > Joel thanks,
>
> > Your reply made sense to me. I hadn’t thought of the possibility of
> > two drive circuits like a split primary mains transformer.  I thought
> > I’d always understood dot notation until I came across some lecture
> > notes from MIT (Massachusetts institute of technology) where the
> > current directions didn’t make sense when applied to forward or fly
> > back circuits.
>
> > I last studied magnetic’s back in the early 90s, so just wanted to be
> > sure I wasn’t loosing my mind!!
>
> > Your response was very helpful, thanks again!
>
> > James,
>
> > I take your point about downloading “mystery files” But as Tim said it
> > was a JPG so no virus issues. Sorry for being critical but you looked
> > at it and I have managed to get a good answer; so I shall not be
> > restricting myself to ASCII drawings in the future!
>
> Sure, we like diagrams, no question about that.  I did not download or
> view yours, but I'm glad you got the answers you wanted from others who did.
>
> > Engineers like diagrams! Why not move with technology, throw caution
> > to the wind and give a video clip in future! Engineers communicate in
> > diagrams so why not on line?
>
> Personally, I prefer pencil and paper.
>
> Cheers,
> James Arthur- Hide quoted text -
>
> - Show quoted text -


>Besides, ASCII art means
>these things get archived, for future seekers.

This it true, but that’s like saying one shouldn’t move from 3.5 inch
floppy disk to DVD. I believe engineers should move with the times and
try and always better the tools they use.

We are in fact communicating via the internet with a VAST amount of
people, something that is impractical with pencil and paper alone. I
did in fact use pencil and paper to produce my drawing, I just scanned
it so all you people could see it.

I prefer forums that enable one to upload diagrams, but I cannot seem
to find any with power supply engineers in.

I apologise for the adverts on the file sharing site, but when I need
a diagram in the future I will be using the same method.

Each to their own and all that...


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