# equivalent series resistance (capacitance) (ESR)

When an AC voltage is applied to capacitors, the capacitor is charged and discharged at the frequency of the AC voltage. The behavior depends not only on the capacitance of the capacitor, but is essentially determined by the losses during each charging and discharging process. Such losses are caused by the ohmic properties of a capacitor and are called Equivalent Series Resistance (ESR).

Equivalent Series Resistance enters the impedance as an unwanted internal resistance along with Equivalent Series Inductance( ESL) and affects power dissipation and noise rejection.

The loss resistance depends on the design of the capacitor and the materials used. It is composed of ohmic, inductive and capacitive resistance and forms a series circuit with the capacitance of the capacitor. It is frequency-dependent and changes due to temperature influences and storage. In the case of tantalum capacitors, electrolytic capacitors or ceramic capacitors, the associated change in the ESR value can be noticeable in circuit terms, since large charging currents flow in capacitors with large capacitances.

The lower the ESR value, the higher the current-carrying capacity of the capacitor. Elcaps with particularly low equivalent series resistance are referred to as low or ultra-low ESR electrolytic capacitors. Because of the lower internal resistance, they have better efficiency. To distinguish between low- and ultra-low-ESR, the series internal resistances of low-ESR electrolytic capacitors are less than 1 ohm, while those with ultra-low-ESR are less than 0.1 ohm, based on 100 kHz. Depending on the structure and electrolyte, ESR values for electrolytic capacitors range from 20 milli-ohms to 100 milli-ohms. For supercapacitors, the equivalent series resistance is between a few milli-ohms and a few tens of milli-ohms.