In this paper, the impact of asymmetry in the injection network of an active EMI filter (AEF) is analyzed. It is shown that ceramic capacitors are not suited as injection capacitors due to their high voltage dependency. But surface-mounted foil capacitors provide a constant capacitance, and their parasitic inductance is only 70 % higher than for ceramic capacitors with similar voltage ratings. In a laboratory setup, the AEF performance can be improved by 20 dB by replacing the injection network based on ceramic capacitors with foil capacitors.
