Fvm. I have already modeled the interaction between the primary (let's call it L1) and the secondary (L2) by coupling them with a spice directive K1 L1 L2 0.995. However spice wouldn't allow me to then couple only the secondary inductor to the third (the auxilary one which we'll call L4) with the statement K2 L2 L4 0.995.
I was able to "model" the transfer of power from the secondary to the auxilary by placing a winding (L3) in parallel with the secondary (L2) with an inductance of an order of magnitude higher in order to decrease it's effect on the secondary side inductance.
I coupled this winding (L3) to the auxilary winding (L4) with the statement K2 L3 L4 0.995. Where the inductances were chosen to set a ratio of 2 between L3 and L4.
The maximum voltage on the secondary (L2) is clamped by the regulated output voltage (5V) so the third winding (L3) which is in parallel with L2 only sees 5V and because the ratio between L3 and L4 is 2 the voltage over the L4 winding will be maximum 10V which is rectified to 10V DC to feed the IC.
This works quite well. So it appears that the auxilary winding voltage is derived with a "second" transformer between the secondary side and the auxilary side where the primary is in parallel with the secondary of the main transformer.
The arrangement in spice as part of my circuit can be seen here. This is a isolated flyback smps
https://imgur.com/4yUBs
Goldsmith, in regards to your post. This IC has a high voltage startup regulator so the scheme you posted is not needed here and it was not what i was asking about. But how the auxilary is woven to transfer power from the secondary to the auxilary winding. But i think i know how now. Thank you for the reply though