Implementation of soft filter damping in control circuitry

Output filters which are used in switching power supplies for reducing switching harmonics have to be properly damped when designing a feedback loop with good performance. A technique that provides filter damping through a control circuit is presented. It is shown that filter damping can be adjusted by incorporating an extra inner current feedback loop. Moreover, in the case of inductive loads, the effective filter damping ratio is directly proportional to the current feedback loop gain. It is also noted that certain functions usually implemented in the power circuit using discrete components can be equally replaced and performed through the control circuit with the same performance and enhanced flexibility. The operating principle of the technique is described, and its performance is evaluated through illustrative examples