A novel hybrid common-mode EMI filter with active impedance multiplication

This paper presents a novel hybrid common-mode (CM) electromagnetic interference filter for a military power supply. The proposed filter is composed of an active impedance multiplication circuit cascaded with a benchmark CM inductor. The active impedance multiplication circuit is very effective in boosting the impedances of both the benchmark CM inductor and the noise source. Thus, the total equivalent impedance of the filter is enlarged by the active booster to a great extent. An important advantage of the approach is that only a small-size CM choke is used as the passive filter instead of a traditional CLC filter. Furthermore, the noise source is turned to be an inevitable part of the hybrid filter by the impedance multiplication effect. Experimental results were carried out according to MIL-STD-461. It is shown that the proposed approach can acquire good noise attenuation performance within a wide frequency range.