Example 7: current compensated chokes

In this example the charakteristics of the magnetizing inductance and the leakage inductance  of a current compensated noise suppression choke are shown.

Current compensated chokes use two (or several) similar windings on a highly permeable ring core through which the current flows in the opposite direction. Thus, the magnetic field cancels itself out.

For common-mode interference current, the choke uses a high inductance, as they are not compensated for.

However, the high permeable cores are saturated very quickly since they do not have an air gap. As the interference current increases, the filter effect of the choke can be rapidly decreased due to the saturation.

This diagram shows the saturation curve of a current compensated choke using a ferrite ring core (2 x 2.7 mH / 8 A, Epcos B82725-A2802-N1). The inductance at a non-compensated current of 100 mA is merely 1.5 mH.

Current compensated chokes also use a leakage inductance that is more or less in magnitude. This is quite desirable since this counter acts the differential mode interference current. The lower diagram shows the leakage inductance of the same choke. Here, the leakage inductance is about 30 µH and is only saturated at a multiple of the rated current.