The unstoppable rise of polymer capacitors
The benefits of polymer capacitors
The reasons for their popularity vary with the application but in general they offer high capacitance in small packages, long life, high reliability, and a host of other desirable electrical characteristics including:
- Good high frequency performance, including low impedance and ESR (Figure 1)
- High ripple current capability
- Stable operation with respect to changes in temperature and bias voltage (Figure 2)
- Elimination of the acoustic noise created by ceramic capacitors (piezo effect)
- Wide operating temperature range, typically from -55 to +105 or +125 degrees C or more
|Figure 1: Murata’s ECAS multilayer polymer capacitors offer lower ESR than other types of polymer capacitor – only multilayer ceramic capacitors are better in this respect||Figure 2: Polymer capacitors are far more stable than class 2 multilayer ceramic components, both with respect to bias voltage and temperature variations|
Overview of polymer capacitor types
Polymer tantalum capacitors offer significant cost savings over traditional tantalum capacitors and don’t suffer from the ignition risk that the latter present. They have lower voltage de-rating yet still provide good volumetric efficiency, coupled with low ESR and ESL, so ripple current ratings are high too. The capacitance range is 0.47 to 1500µF at rated voltages from 2.5 to 125Vdc. The ESR can be as low as 5mOhms and ripple current ratings can be 4A or more for some devices.
Polymer aluminium of a wound construction in a metal can come in values from 3.3 to 4700µF with voltage ratings from 2.5 to 125Vdc. They have lower capacitance per unit volume and higher leakage current than conventional aluminium electrolytic capacitors but this is offset by an ability to withstand high ripple current, low ESR and much longer operating life.
Polymer hybrid capacitors are designed to combine the advantages of aluminium electrolytics with conductive polymer components, primarily the low leakage current of the first with the long operating life, low ESR (down to 14mOhms) and high ripple current capability (up to 4.34A) of the second. They’re sometimes called Polymer Lytic components. Capacitance values range from 6.8 to 1000µF and voltage ratings from 6.3 to 125Vdc.
Polymer aluminium multilayer capacitors are low voltage devices, rated from 2 to 25Vdc, and are available in values from 6.8 to 1000µF. ESR is very low – down to 2mOhms - and ripple currents can exceed 7A in some types.
Avnet Abacus represents the world’s leading manufacturers of polymer capacitors including AVX (acquired Nichicon Polymer range), KEMET (including NEC Tokin), Murata, NIC, Panasonic (former Sanyo products), Rubycon and Vishay (acquired Holystone Polymer range).
A detailed white paper from Panasonic that explains the technologies of several polymer capacitor types can be downloaded here.
If you don’t mind registering your contact details, Murata has a good tutorial on polymer aluminium capacitors vs tantalum capacitors here.
Additionally, KEMET have an interesting technical piece on bringining the benefits of polymer tantalum capacitors to high-voltage, high reliability markets here.
If you need application advice or want to request samples, our pan-European team of technical specialists is always on hand to help. Visit the Ask an Expert page to get in touch.