# Direction of winding (clockwise/anticlockwise) in flyback transformers

Here is a circuit of offline switching power supply based on Viper22a IC:

In this circuit and many other similar circuits, they denote the starting of a winding by a "dot". However they never mention the direction of the winding - clockwise or anticlockwise.

Does the direction of winding not affect the circuit in any ways?

I tend to believe that polarity of induced voltage should be dependent on the direction.

In case the direction of winding changes the polarity, is there is a standard winding direction to be followed while making the transformer? Example - Does the circuit given above assumes this pattern?:

Primary: start at 2 - End at 1 -> Clockwise

Auxiliary: start at 3 - End at 4 -> Clockwise

Secondary 1: start at 5 - End at 6 -> Clockwise

Secondary 2: start at 8 - End at 7 -> Clockwise

• Clockwise winding from one end of the coil is the same as anti-clockwise winding from the other end. Commented Mar 21, 2016 at 7:10
• I improved the example. Please see and let me know if my assumption is correct. Thanks Commented Mar 21, 2016 at 7:16

Clockwise or anti clockwise is unimportant providing all windings use the same method - the dot tells you that if a wire was wound clockwise the corresponding wire on a different winding was also wound clockwise. So all winding wires with dots produce voltages that are in phase.

There are several factors that could be thought to affect the performance of a multi-winding transformer.

a) the handedness of each winding
b) the polarity of each winding with respect to the others
c) where each winding starts and finishes

Handedness

In practice, the handedness of each winding, CW or CCW, cannot be specified, as there is no reference! If you hold the core this way up, any given coil may be CW. However if you hold the core the other way up, it would be CCW. Which is right? The magnetic circuit is a loop, it doesn't have a 'this way up' end!

If you take the first winding as the reference, and record whether the other windings use the same or opposite handedness, then there is no observed influence on the performance of the complete transformer (but see caveat below).

Polarity

If we choose one coil as a reference, and then record whether each other coil is wound in the same of the opposite direction, then we have to define which polarity of the reference coil we are taking as reference. This needs one of its wires marking somehow, and a dot at the start is as good as any other. A dot at the start of each other winding completely defines their mutual polarity.

Starts and finishes

For some transformers, where inter-winding capacitance is important, it is necessary to know which end of a winding is nearest to another winding, or to the core. For the first winding to go on, we know the 'start' wire will have highest capacitance to the core, and the finish wire have highest capacitance to the next winding, or the interwinding screen.

Caveat

We are talking about a transformer here. This is a structure that is very small compared to a wavelength of the signals passing through it, and that has a pair of multi-turn windings linked by a high permeability magnetic loop.

If we deconstruct the transformer to such an extent that it is a few turns of wire with a manifest helix structure with no loop of high permeability magnetic material, and drive it with a high frequency signal such that the windings work like antennae, then the full geometry of the windings will affect the performance slightly, including whether the windings are wound in the same or opposite direction.

Your explanation of handiness is wrong, a CW wound coil is a CW wound coil, even upside down, same for CCW. Consider a CCW coil wound on a straight core; if the top end comes over the top from the right, and the bottom end leaves on the bottom over the top and off to the left. Flip it around, and nothing has changed.

When you leave the power connected and rotate the coil, the magnetic field stays aligned in the way that you describe, but its the direction of current flow that is being rotated. If you disconnect the coil, flip it, and reconnect it in place, then the direction of field is consistent because the path that the current takes doesn't change.