# Transformer dot convention question

#### psoke0

Joined Mar 31, 2017
174
hello guys i have questions about transformers. should secondary wire wound direction be the same as primary or opposite. i have learned so for if i learned correctly that if the direction is the same the dot convention will be the same for both. ( and flux will add to each other (not sure about this) . my question is is there a worng winding direction or is it doesnt matter which way you wound it besides voltage polarity change in secondary. i mean if i wound it around in opposite is it bad or good is there correct way of wound it ? thank you

#### KeithWalker

Joined Jul 10, 2017
1,917
The dot in transformer diagrams is just a convention to indicate the start of each winding if they are all wound in the same direction. If one winding is made in the opposite direction, the dot will then be on the finish, so then the winding will then be in the same direction as the other windings. The direction it is physically wound in will make no difference to the transformer's properties.

#### crutschow

Joined Mar 14, 2008
27,718
And the dots thus indicate that the voltage phase at all the dot wires are the same.

#### AlbertHall

Joined Jun 4, 2014
11,504
For AC power transformers the winding direction doesn't matter except if you are connecting two windings in series or parallel.
Where the phase matters (for instance oscillator with feedback winding, forward or flyback converter) then you do need to take account of the winding direction as indicated by the dots.

#### psoke0

Joined Mar 31, 2017
174
okay thank you guys i understand the AC side of it now .
For AC power transformers the winding direction doesn't matter except if you are connecting two windings in series or parallel.
Where the phase matters (for instance oscillator with feedback winding, forward or flyback converter) then you do need to take account of the winding direction as indicated by the dots.
can you please explain a bit more about feedback winding flyback or forward. how does it effects it

#### AlbertHall

Joined Jun 4, 2014
11,504
In the oscillator circuit below, if the feedback winding is the wrong way round then you have negative feedback instead of positive and it won't oscillate (though this diagram doesn't show the dots).

Here is a flyback converter (note the dots here). The output is generated when the transistor switches off.

A forward converter is similar but the output is generated when the transistor switches on so the dots are switched.

#### psoke0

Joined Mar 31, 2017
174
In the oscillator circuit below, if the feedback winding is the wrong way round then you have negative feedback instead of positive and it won't oscillate (though this diagram doesn't show the dots).
View attachment 232706
i see so in oscillator it should be wound in opposite direction for oscillation

Here is a flyback converter (note the dots here). The output is generated when the transistor switches off.

View attachment 232707

A forward converter is similar but the output is generated when the transistor switches on so the dots are switched.
View attachment 232708
what is the differance between output generated when switch is off versus on is there an advantage over each other why they do that why not just only use forward converter when output generated when switch is on is there a need in flyback

#### AlbertHall

Joined Jun 4, 2014
11,504