switch-mode-power-supplytransformer
I am researching about SMPS, specifically AC/DC flyback converters.
In the datasheet for the switching controller (Fairchild FSCQ0765), it refers to an auxiliary winding. What is that? All the current transformers I've looked at only have a primary and secondary winding.
1) Winding direction doesn't matter as long as you keep it consistent. If you are adapting a lathe or drill as a winder, the winding direction will be determined by the machine.
2) If the small windings are at approximately the same potential they can share a layer, otherwise you must provide sufficient insulation between them. Sometimes you may have to separate layers to reduce capacitance between them, or interleave them to reduce leakage inductance, but that is too complex to discuss here.
3) Winding coils side by side is simpler and provides better voltage isolation especially when the sections are different bins on the bobbin. That is essential for high voltage supplies and makes mains voltage safety approval easier.
However it increases the leakage inductance, and that matters for high frequency applications like SMPS. The only reasonable way to know if you can do this is to wind one that way and measure the leakage inductance. If it's out of spec (or even close to it) wind another in layers and compare them.
Winding from top to bottom or bottom to top does not change the "dot" (which represents the direction of the magnetic north/south pole for a given current direction).
You can use the "right hand rule" to keep this straight.
Place your right hand around the coil with your fingers in the direction of current flow. Your thumb points to the North magnetic pole. The ends with the "dot" will be the ones that create the same direction of magnetic field when current flows from that end to the other.
Best Answer
The auxiliary winding is the one that is not a primary or secondary.
In this case it provides power and a timing signal (synchronization) to the controller- since it's a quasi-resonant controller it needs to be in tune with the transformer.