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common-mode-Slide8

Shown in the top left corner the ‘component’ trying to be created from the previous page has been copied over for reference. Although not shown previously any ‘real’ mutually wound magnetic (CM chokes, transformer) will have some amount of uncoupled flux or leakage inductance which effects the coupling of the magnetic. This is depicted in the drawing in the top right corner which shows some flux, blue lines, escaping the core and not coupling to the adjacent winding. In a standard common mode choke this leakage inductance is very low and can therefore be ignored. However, in the integrated common mode differential mode choke trying to purposely increase the amount of leakage in the core and therefore the reluctance model of the CM choke can be redrawn, as shown in the bottom left corner, with a reluctance RC representing the path taken by the uncoupled flux or leakage. It should be noted that at one extreme, with a very high RC reluctance, there would be very little flux flowing through this element and one essentially has an ideal common mode choke. At the other extreme, with a very low RC reluctance, all of the flux from each winding would be uncoupled from the other winding and essentially one would have two separate and uncoupled inductors. In the bottom right corner the schematic from the top left is just redrawn in a more standard ‘transformer’ type format.

PTM Published on: 2014-10-17