Aluminum Organic Polymer Capacitors

2016-02-02 | By Dave Knight

Aluminum organic polymer capacitors make major improvements over traditional liquid-electrolyte-based aluminum electrolytic capacitors. This paper describes the advantages and disadvantages of traditional electrolytic capacitors, and explains how organic polymer capacitors offer improved performance.

Traditional capacitors

Aluminum electrolytic capacitors have been the go-to technology for large filter capacitors for rectifiers and power converters for years. They have high capacitance per volume and per dollar. Their drawbacks are equivalent series resistance (ESR) and a short lifetime.

Dry-out mechanism

Electrolytic capacitors use a liquid electrolyte that evaporates over time, resulting in decreased capacitance. Decreasing the ambient temperature and the ripple current can extend the lifetime of the capacitor—doubling it for every 10 C drop.

ESR

Ripple current generates heat, which causes a temperature rise and dries out the electrolyte. Also, the ripple voltage of power converters is dominated by the ESR of the filter capacitors.

Organic Polymer Capacitors

Long lifetime

Organic polymer aluminum capacitors have the same basic construction of aluminum capacitors, but replace the liquid electrolyte with a solid, organic polymer electrolyte. This results in a capacitor without a dry-out mechanism and, instead of doubling the lifetime with each 10 C drop, the same temperature change increases the lifetime of organic polymer capacitors by five times.

Reduced ESR

Organic polymer capacitors have up to five times less ESR than similarly sized electrolytic capacitors. Reduced ESR means fewer capacitors are required to do the same job—they run more efficiently and improve the frequency response of the capacitor. ESR is also more stable over temperature than aluminum capacitors, whose ESR increases dramatically at cold temperature. ESR is also more stable over frequency.

Improved ripple current rating

Polymer capacitors have up to six times higher ripple current rating than similar aluminum capacitors.

Improved capacitance for size

Organic polymer capacitors are up to five times smaller, or can contain up to five times the capacitance in the same volume.

Improved stability over temperature

Traditional electrolytics lose capacitance in low temperature, resulting in increased ripple voltage.

Conclusions

Aluminum polymer capacitors have many advantages over traditional aluminum electrolytic capacitors include smaller size, large capacitance, larger ripple current rating, and improved stability over temperature and frequency. Aluminum polymer capacitors are available at DigiKey from major capacitor vendors such as Nichicon, Panasonic, Vishay, and United Chemi-Con.

More information about aluminum organic polymer capacitors and specific product lines can be found in these training videos:

FPCAP Conductive Polymer Aluminum Capacitors

Polymer Capacitors

PX/PS Conductive Polymer Capacitors

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