The equivalent series resistance or ESR of a capacitor is particularly important in many applications. One particular area where it is of paramount importance is within power supply design for both switching and linear power supplies. In view of the high levels of current that need to be passed in these applications, the equivalent series resistance, ESR plays a major part in the performance of the circuit as a whole.
The ESR of the capacitor is responsible for the energy dissipated as heat and it is directly proportional to the DF. When analysing a circuit fully, a capacitor should be depicted as its equivalent circuit including the ideal capacitor, but also with its series ESR.