Abstract

A compact and efficient design of the electromagnetic interference (EMI) input filter is one of the main challenges in a high-density switching regulator, and is critical to achieving the full benefits of electrification in automotive, enterprise, aerospace and other highly constrained system environments. As examples, automotive on-board chargers and server-rack power supplies are high-power applications where it is important that the volumetric reduction of EMI filter components helps the solution fit into challenging form factors, especially with the advent of wide-bandgap (gallium nitride [GaN]- and silicon carbide [SiC]-based) power semiconductor devices with fast switching characteristics that potentially lead to higher common-mode (CM) emissions.

CM filters for both commercial (Class A) and residential (Class B) environments typically have limited Y-capacitance because of touch-current safety requirements, and thus require large-sized CM chokes to achieve the requisite attenuation – ultimately resulting in filter designs with bulky, heavy and expensive passive components. The deployment of active EMI filter (AEF) circuits enables more compact filter designs for next-generation power-conversion systems. Space-constrained applications, such as those mentioned above, are ripe for even further optimization by leveraging active power-supply-filter integrated circuits (ICs) to significantly reduce magnetic components and overall filter size.

This technical white paper frames the theoretical background and general principles of AEF circuits in terms of sensing, injection and control techniques, with practical circuit realizations using a family of stand-alone AEF ICs from Texas Instruments for CM noise cancellation in single-phase and three-phase AC power systems. Measured results from a 3.3-kW power factor correction (PFC) AC/DC regulator will illustrate the benefits of EMI mitigation and board space savings.