Abstract

Some current sensing applications in the metering and power conversion space require DC current sensing alongside the AC current sensing. The DC often is an unwanted or false signal content which needs to be detected, measured, and removed. For instance, in AC power systems, DC energy dissipates in a transformer as heat because DC energy cannot be transferred across the transformer. This energy dissipation creates power losses and thermal problems. Current sensing in such applications can be realized by a shunt-based approach measuring the voltage drop across a small value sense resistor. DC signals within the AC are very small and challenge the dynamic range of a system. This application note introduces a preconditioning filter circuit to relax those requirements and improve the DC in AC measurement.