KEMET’s new aluminum solid polymer capacitor series utilizes a solid polymer electrolyte instead of a conductive liquid electrolyte. Traditional aluminum electrolytic capacitors utilize conductive liquid electrolytes, so these are often described as “wet” capacitors. The benefits of solid polymers include a low ESR that is stable across temperatures, frequencies, and operational lifetime. This means that they are capable of higher ripple currents and longer lives than “wet” capacitors. Additionally, the solid polymer makes them much more vibration resistant, when packaged properly.
Figure 1: KEMET’s Aluminum Solid Polymer Electrolytic Capacitors, in Through-hole and Surface Mount
Capacitors, in general, are two conductive plates (electrodes) separated by an insulator (dielectric). Electrolytic capacitors are polarized, meaning they only work when one terminal is always at a more positive voltage than the other terminal. If a reverse voltage is applied, the capacitor could be damaged.
Figure 2: Basic electrolytic capacitor concepts
In an aluminum electrolytic capacitor, the electrodes are made out of aluminum foil, and between the two aluminum electrodes is an electrolytic paper saturated with a conductive liquid electrolyte. An oxide layer on one of the electrodes (the anode) is the dielectric. The other foil electrode is called the cathode.
By contrast, in an aluminum polymer capacitor, the electrolyte is a solid polymer material. This electrically conductive polymer material lowers the ESR, increases temperature stability, and lengthens expected life. The solid polymer’s electrolyte also does not fail by drying out, as “wet” electrolytes can.
Figure 3: Aluminum electrolytic capacitor with solid polymer electrolyte
The solid organic polymer used as the electrolyte in these new solid polymer capacitors is an order of magnitude more conductive than traditional liquid electrolytes. This means that they have superior electrical characteristics.
Solid polymer capacitors have very low ESR due to the high conductivity of KEMET’s proprietary organic polymer material and the solid polymer cathode construction. Low ESR means that as the capacitor is doing its job, very little power is wasted as heat.
Because high ripple current through a capacitor’s ESR causes power to be dissipated, lower ESR equals less power dissipated in the capacitor, which in turn keeps the capacitor temperature lower and makes it more usable in high temperature applications and gives it a longer life. Ripple current through ESR also creates noise voltages on the rail, so lower ESR means less noise in the same application.
The solid polymer electrolyte is highly stable across different operating frequencies, operating temperatures, and over the life of the capacitor. A polymer capacitor has low ESR across a broad spectrum of frequencies, meaning harmonics are not sources of undue heating and power loss.
Another advantage of the solid polymer electrolyte is that the capacitance is more stable over the operational life of the product. Traditional “wet” aluminum electrolytics lose capacitance at a much higher rate.
With life expectancies of up to 5,000 hours at 105°C, they far outpace traditional aluminum electrolytics. Even better, the life expectancy increases by an order of magnitude (ten times) for every 20°C the capacitor’s operating temperature decreases.
KEMET’s A768 series of solid polymer capacitors are specially designed to be resistant to vibration forces up to 30G. Besides all the benefits of polymer capacitors mentioned above, the solid polymer is also more internally structurally stable, implying it can survive higher vibration. But to realize that potential, certain design choices were made to take advantage and create the A768 series.
Together, the solid polymer construction, the taller base, and the extra “dummy” terminals offer a product that is capable of withstanding up to 30 G of vibration. These parts are offered in 10 mm diameter and are AEC-Q200 automotive qualified.
There are many applications that benefit from rugged capacitors that are capable of operating in high vibration environments. One of the best applications is power converter circuits in automobiles. As more electronics are put into vehicles, and more parts of vehicles include electrical systems, the need for high reliability power conversion in extreme conditions increases.
New electric cars need an enormous number of power conversion circuits, from the charging and maintaining of the batteries, to delivering power to the drive train and control systems. The vibration from the moving parts of the motors, axles, wheels, and road surfaces is tough on every part of a car. With KEMET’s anti-vibration series of capacitors, electrical subsystems, engine control units, and automotive DC/DC converters can operate more reliably for longer than ever before.
KEMET’s A768 series comes in capacitances from 18µF up to 1000µF, and in voltages from 16 V up to 80 VDC. With a wide operating temperature range, from -55°C up to 125°C, the automotive AEC-Q200 qualification, and the anti-vibration packaging, these capacitors are ideal for most power conversion applications, especially in vehicles and industrial machine applications.
KEMET’s aluminum polymer capacitors are halogen-free and compatible with standard lead-free solder assembly processes.