Buck-boost converter confusion

[khatus]

Hello, guys

I am trying to understand the basic concept of flyback transformer.I have read that The flyback converter is based on the buck-boost converter.with the switch realized using a MOSFET and diode.

Here is the picture of typical buck-boost converter


Next the inductor winding is constructed using two wires, with a 1:1 turns ratio.



Then It looks something like that


Next, the connections between the two windings are broken. One winding is used while the transistor Q1 conducts, while the other winding is used when diode D1 conducts.
Now look at the dotted terminals of both coils


After changing the position of the switch the dotted terminals of coils also changes.

My question is why this change happens from figure-3 to figure-4 ??

I know, Unlike the ideal transformer, current does not flow simultaneously in both windings of the flyback
transformer.

[T3sl4co1l]

Flip the right-hand side upside-down.  It's just a polarity convention (in Fig.4).

Tim

[ocset]

the familiarity with the buckboost isn't absolute...but its kind of very similar.....
If you want to know hows and whys of flyback then running the LTspice sims of flyback as attached is a good way.
The feedback loop equations for flyback and buckboost are very similar due to their  similarities.
Both the flyback and buckboost operate as "alternate shovellers"....ie, ,they shovel power in, then they shovel power out..etc etc at the switching frequency.....unlike say a full bridge which shovels power in, then rests, then shovels power in, then rests...etc etc
Of course this means that the flybak and bukboost both suffer the dreaded right half plane zero

[mikerj]

After changing the position of the switch the dotted terminals of coils also changes.

Not just the switch!  The polarity of the diode is also changed, and therefore the polarity of the output terminals.