# Current Rating in Common Mode Choke

What is the meaning of this current rating which says "unbalanced" current? I know in common mode chokes the common mode current rating is given. Why here it is written as Iunbal.?

• Sorry it is confidental Commented Apr 2 at 8:09
• I don't find the exact part, but this seems similar enough for sake of discussion: vacuumschmelze.com/03_Documents/Datasheets%20-%20Drawings/… Commented Apr 2 at 8:48
• How to confuse an engineer as another engineer: Use balanced/unbalanced, differential-mode/common-mode, and longitudinal/transverse current interchangeably everywhere. Commented Apr 2 at 11:26

What is the meaning of this current rating which says "unbalanced" current?

It's the numerical magnitude difference between current into pin 4 and, current out of pin 1: -

I know in common mode chokes the common mode current rating is given. Why here it is written as Iunbal?

Yes, it can be a little confusing how one supplier says one thing and, another supplier uses a different phrase. In this scenario, the common-mode current is half of $$\I_{UNBAL}\$$ so, you could argue that maybe what is going on is a little bit of specsmanship: -

Specsmanship is the use of specifications or measurement results to suggest or establish putative superiority of one entity over, especially when it is inappropriate. It is commonly found in advertising of high fidelity audio equipment, automobiles, digital cameras, electronic display devices, and other merchandise.

A search on the manufacturer's website would prove fruitful:
EMC Products based on Nanocrystalline VITROPERM | VACUUMSCHMELZE
we find Saturation Behavior on page 10.

CMCs are also known as current-compensating chokes, because the main load current flows equal and opposite between the two (or more) windings, greatly reducing the energy stored in the core and allowing high-permeability materials to be used. (Energy storage goes inverse with permeability, while impedance is proportional to it.)

Magnetic saturation means inductance drops sharply, and the choke no longer chokes AC at that point. Avoiding saturation is important to intended CMC operation.

Unbalanced current, means current returning through the load through a path other than the two windings; the winding currents are no longer equal and opposite, but unbalanced. This rating tells how much is permissible before saturation becomes significant (inductance drops by some ratio). -30% is a typical amount, but unfortunately they don't seem to define what ratio they are counting.

Balanced currents in the windings will cancel out and cause a net zero flux in the core of the choke. The main limit here is thermal due to the resistance of the windings.

However, unbalanced currents will cause a net flux that can easily saturate the core if they exceed the limits shown in the data sheet. If the core is saturated the inductance will drop to a low value.