Using electrolytic caps to dampen the system

By Dr. Min Zhang, the EMC consultant

Sometimes, the larger ESR of an electrolytic capacitor is not a bad thing. In certain applications, we need to have some resistive components to provide damping of the system. A typical example is presented here.

Resonance is often seen in a system that is caused by input cable inductance and the input ceramic capacitors (which generally have very small ESR value). One effective way of preventing this from happening is to add an electrolytic capacitor in between. The ESR of the electrolytic capacitor makes the system more stable. An example is simulated below, where there is a two-meter cable between the voltage source and the circuit. We simulated two scenarios, one without the electrolytic capacitor and one with. The step response shows that the system is damped by the electrolytic capacitor.  

Simulation of an electrolytic capacitor’s damping capability
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