During EMC power supply circuit design, common-mode interference is the most difficulties encountered, common mode inductor is one of the major methods on solving interference signals.

Here let's talk about the basic principles of solving EMC artifacts from design plan in this way.

A common mode inductance, is wound both line and neutural windings on a single core.

While the magnetic flux in the magnetic core accumulates when passing through the common mode current, then has a large inductance, which has a suppressing effect on the common mode current.  However, there is no influence on differential-mode chokes.

Thus, the common-mode choke can reasonably suppress the common-mode interference data signal in the balanced route, but has no harm to the differential-mode data signals normally transmitted in the route.

We need consider below details carefully while making common mode inductors:

1. To avoiding the electromagnetic coil with short-circuit faults under the effect of instantaneous speed over voltage, the winding coils must be insulated from each other;

2. The inductance's skeleton doesn't request to be a saturate state when electromagnetic coils pass through the instantaneous speed and large current;

3. To avoiding penetration, the skeleton & coils must be insulated with each other;

4. To reducing parasitic capacitance &improving coil's ability to work against instantaneous speed over-voltage, both coils and coil inductance should be single-sided.