ESR

ESR stands for Equivalent Series Resistance and refers to the resistance connected in series with an ideal, lossless capacitor. It represents the magnitude of the resistance connected in series with an ideal capacitor and effectively doubles the performance of an actual capacitor. In general, the lower the ESR value (equivalent series resistance), the higher the quality of the capacitor and the greater its effectiveness as a filtering device. ESR is a primary factor in determining the ripple of a switching power supply.