Direct Current Losses at the Output Filter of a Switching Controller

Both AC/DC and DC/DC switching controllers have a residual ripple in their voltage on the output side, caused by parasitic series resistance ESR and the parasitic inductance ESL of the output capacitor that can create interference in subsequent components and cause electromagnetic malfunctions. In practice, LC low-pass filters are normally used to reduce residual ripple to a few millivolts and suppress high-frequency portions. Figure 1 shows such a low-pass filter that can be used in connection with an unshielded coil, a WE-PD2 and a conventional electrolytic capacitor.