# Transformer dot notation

Discussion in 'Electronic Design' started by reggie, Jun 11, 2008.

1. ### reggieGuest

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

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.

reggie, Jun 11, 2008

2. ### James ArthurGuest

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
>
>
> 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

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

James Arthur, Jun 11, 2008

3. ### Bob EldGuest

"reggie" <> wrote in message
news:...
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

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.

Bob Eld, Jun 12, 2008
4. ### Tim WilliamsGuest

"James Arthur" <> wrote in message
news:GtW3k.46590\$bs3.22826@trnddc07...
>
> That's a lot of words, a splash ad site, and a mystery

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

Tim Williams, Jun 12, 2008
5. ### reggieGuest

On 12 Jun, 06:30, "Tim Williams" <> wrote:
> "James Arthur" <> wrote in message
>
> news:GtW3k.46590\$bs3.22826@trnddc07...
>
>
> > That's a lot of words, a splash ad site, and a mystery

>
> Mystery?  It's a JPG, like the man said.  I'm viewing it in L-View Proright
> 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,

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,

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.

reggie, Jun 12, 2008
6. ### James ArthurGuest

Tim Williams wrote:
> "James Arthur" <> wrote in message
> news:GtW3k.46590\$bs3.22826@trnddc07...
>> That's a lot of words, a splash ad site, and a mystery

>
> 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

James Arthur, Jun 12, 2008
7. ### James ArthurGuest

reggie wrote:
> On 12 Jun, 06:30, "Tim Williams" <> wrote:
>> "James Arthur" <> wrote in message
>>
>> news:GtW3k.46590\$bs3.22826@trnddc07...
>>
>>> That's a lot of words, a splash ad site, and a mystery

>> 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,
>
> 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

James Arthur, Jun 12, 2008
8. ### reggieGuest

On 12 Jun, 23:27, James Arthur <> wrote:
> reggie wrote:
> > On 12 Jun, 06:30, "Tim Williams" <> wrote:
> >> "James Arthur" <> wrote in message

>
> >>news:GtW3k.46590\$bs3.22826@trnddc07...

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

>
> > 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...

reggie, Jun 13, 2008
9. ### James ArthurGuest

reggie wrote:
> On 12 Jun, 23:27, James Arthur <> wrote:
>> reggie wrote:

>>> James,
>>> 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
>>

>
>
>
> 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.

Since you don't know me, I've added a smiley face to my paper-and-pencil
comment above.

> 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.

Here we post pictures to alt.binary.schematics.electronics, then alert
folks to this in our posts to sci.electronics.design. That's not
perfect though, since many people can't get binary newsgroups.

> 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...

No need to apologize.

That site you used was just a little pushy. It immediately pops up and
prompts with a download window. That's actually convenient, but
speaking of keeping up with the times, surely you understand that thanks
to Bill Gates, following a link to a new site full of ads that
is reason for pause?

For example,
http://www.secureworks.com/research/threats/jpegvirus/

Anyway, it turns out you're a good guy, it's a decent website, etc., etc.