Loss-Free Output Ripple Filter

Switching controllers exhibit a residual ripple in their output, which disturbs downstream assemblies and may cause electromagnetic interference. Output filters are therefore often used for interference suppression, which may, under certain circumstances, exert an influence on the control loop. Compensation of the control loop may be required to prevent losses in output power. Irrespective of which switching controller topology is in use, the output current causes unwanted residual ripple through the parasitic series resistance ESR and the parasitic inductance ESL of the output capacitor. A relatively large residual ripple arises which depends on the capacitor type selected and has different waveforms.