Interpretation of ratings for electrolytic capacitors

Electrolytic capacitors do not arouse much analytical interest and yet they represent a significant proportion of the cost of most power electronic systems. It is therefore of benefit to fully utilise their ratings. Ripple current ratings for electrolytic capacitors are usually provided for operation at 85/spl deg/C ambient. A particular capacitor can be operated at higher currents with lower ambient temperatures. However, manufacturers' data is often insufficient to readily determine appropriate values. This paper seeks to clarify the relationship between ripple current, operating temperature and life and thereby to enable the designer to make an informed choice. In addition the general relationship between voltage ratings, current ratings and capacitance is examined.