As shown in the above figure, 1 and 3 are one winding, 2 and 4 are one winding, 1 and 2 are starting pins on the same side of the magnetic ring, and 3 and 4 are ending pins on the other side of the magnetic ring. The number of turns of the two windings should be the same, and the inductance and resistance values should meet the requirements. It should be noted that in case of more turns, the wire is long. In normal winding, it is customary to fold the wire in half and hook it from the middle to both ends. Although this can improve the winding efficiency and avoid damaging the wire in the process of drawing because the wire is too long, it is easy to confuse the direction of the starting wire because it is wound from the middle to both ends, This winding method is not suitable for the winding of common mode inductance coil. Although it is arranged in two layers, and the final end lines return to the position of the starting line, it can be found that the end lines of the two windings are distributed on both sides of the magnetic ring, which does not meet the requirements of in and out. In other words, for inductance winding of the common mode magnetic ring, the length of the starting wire head needs to be reserved, one is pulled to the end, the starting wire is on one side of the magnetic ring, and after winding, the ending wire should also be on the same side of the magnetic ring.