What is Active EMI filters?

An active EMI filter uses active electronic components such as transistors, operational amplifiers, voltage converters, etc., in conjunction with passive components to suppress conducted EMI in the electronic circuit. This filter requires an external power supply for its operation. The active filter first senses any high-frequency noise on the supply lines and then generates noise-canceling currents. These noise-canceling currents are injected back into the supply lines to cancel out EMI. This EMI filter typically consists of a noise sensing circuit, resonant controller, noise injection circuit, and other supporting components/circuits to suppress noise and ensure stability. The active EMI filter ICs typically come with inherent protection features such as UVLO protection and thermal protection.