Aging & In-circuit Characterization of AL-Electrolytic Capacitors

This paper describes the characterization of aluminum electrolytic capacitors specifically used in AC-DC power converter applications. It will be discussed why this capacitor technology is critical regarding lifetime and why it cannot be substituted simply by any another capacitor technology. Different aging effects of the capacitor will be discussed. Usage of the capacitor in different AC-DC converter topologies will be presented. Simulation circuits will be used to analyze the capacitor in more detail before suitable measurements will be performed to demonstrate a real example of a switching-mode power supply (SMPS).

After the introduction into the aluminum electrolytic capacitor basics and theory, this paper will also present all important and possible measurements of capacitor parameters, like capacitance, equivalent series resistance (ESR) and ripple current. This includes in-circuit measurement which can be performed with an oscilloscope. An LCR-bridge is used to obtain high accuracy measurements in addition. A comparison between the two measurement methods will be presented. Furthermore, the required measurement hardware for the in-circuit measurements and the bridge measurement will be discussed and presented.

Lastly, two different lifetime calculation methods are presented and a real example is used to compare the advantages and disadvantages of the different methods.

Thanks to Mr. Frank Puhane from Würth eiSos GmbH & Co. KG who provided me with all aluminum electrolytic capacitor samples including the prepared capacitor with build-in temperature sensors to perform all measurements. Furthermore, his great expertise was very beneficial and helpful to create this premium application note.