Using Leakage Inductance to Optimize EMI Filter Performance In theory, all magnetic flux in an inductor should remain confined within the core. In reality, winding constraints often cause part of the flux to leak, particularly when coils are not fully or tightly wound. Common-mode inductors are especially prone to this effect due to the spacing between their two windings. This leakage flux creates differential-mode inductance, allowing common-mode chokes to attenuate differential-mode interference. Filter designers frequently utilize this phenomenon. In some standard filter designs, only a common-mode inductor is required, as its leakage inductance suppresses differential-mode current effectively. In more advanced applications, designers may increase the leakage inductance deliberately to improve differential-mode attenuation and achieve better overall EMI filtering results.