Critical core parameters in the design of common mode suppression chokes

The effective suppression of common mode chokes does not meet up to their expectations in a great number of cases. The only explanation given in standard texts is saturation. This saturation phenomenon is studied in this paper, in particular saturation due to excessive EMI current. It is shown that a relationship exists between the H-field induced in the core and the suppression effect of the choke. By estimating the suppression required in a particular equipment, it is shown that it is possible to reach optimum core parameters.