Reduction of CM Conducted Emission With a Small Dummy Leg and the Delay Compensation Technique

Passive EMI filters are usually placed at the input of power circuits to attenuate the conducted emission delivered. However, their volume may not be negligible, especially when targeting power automotive applications. The output delay compensation technique may or may not reduce the CM conducted EMI at low frequency, as a fine alignment of the output voltage phases should be achieved. This paper aims at improving the already proposed technique by exploiting a small dummy leg. In such a way, switching losses and cost of the auxiliary circuit required to implement the delay compensation technique can be reduced. From the circuit analysis, it was found that the small dummy leg can achieve a 40 dB CM EMI reduction up to 5 MHz, with one seventh the switching losses of a traditional auxiliary leg.