What is Polymer Capacitor : Working & Its Applications

Polymer capacitors are one type of electrolytic capacitors and these are an excellent choice for any design that needs long life, stable capacitance, small size & high reliability. Polymer capacitors include conductive polymer in an aluminum layered design. These capacitors provide long-term reliability, lower ESR, several package options in between 2.2 – 470 microfarad & also some special features like a conductive polymer in place of a liquid electrolyte. These capacitors have very good behavior against voltage & temperature bias effects and also good aging characteristics. So this article discusses an overview of a polymer capacitor – working and applications.

What is Polymer Capacitor?

The definition of a polymer capacitor is; a capacitor that uses solid polymers like the electrolyte is known polymer capacitor. These capacitors replace electrolytic capacitors in most cases if the maximum rated voltage does not go beyond.

As compared to normal electrolytic capacitors, these capacitors’ voltage is lower typically up to 35 volts, even though some types of polymer capacitors are fabricated with maximum operating voltages like up to 100 volts DC. As compared to electrolytic capacitors, this capacitor has a number of superior qualities like fewer losses, a longer lifetime, and a safer failure mode.

Construction of Polymer Capacitor

The construction of a Polymer capacitor can be done by sandwiching a separator sheet including the electrolyte in between two terminals like anode and cathode where the anode is made with an aluminum foil & the cathode is made with a conductive polymer.

After that, the assembly of this capacitor can be rolled into a cylindrical shape. Electrodes are included and after that, the whole assembly is encased within an aluminum casing.

Since these capacitors are not considered components that are possible to be replaced within a device, then they are frequently made in Surface-Mount Technology (SMT). So this allows them to occupy less space on the Printed Circuit Board (PCB).

Ordinary electrolytic capacitors have opening casings through a pre-scored surface which will smash in case of high pressure and emit the gases formed within the casing in a secure way to avoid detonation in case of overheating. Generally, there are no such vents or scorings on these capacitors because there is no significant force increase in case of breakdown.

How Does Polymer Capacitor Work?

The working of polymer capacitors can be done by using conductive polymers like the electrolyte. These capacitors use solid polymer electrolytes in place of gel or liquid electrolytes that are found in normal electrolytic capacitors. So by using solid electrolytes, the electrolyte drying can be avoided completely. Here, this drying is one of the main factors that limit the life span of normal electrolytic capacitors.

Types of Polymer Capacitor

There are different types of polymer capacitors which include layered polymer, wound polymer, polymer tantalum, and polymer hybrid aluminum capacitors.

Layered Polymer Aluminum Capacitors

These capacitors use conductive polymer as the electrolyte. The voltage supply of these capacitors ranges from 2 to 25V based on the particular model. The capacitance offered by these capacitors ranges from 2.2 to 560µF. The main characteristic of these capacitors is very low ESR (equivalent series resistance). Some polymer capacitors have low ESR values like 3mΩ.

These capacitors are packaged within molded resin-like compact SMT devices. So these capacitors are used in handheld electronic devices otherwise other applications require a low-profile capacitor that will not interfere through a close-by heat sink.

Wound Polymer Aluminum Capacitors

These capacitors mainly depend on aluminum & conductive polymers however they have a wound foil construction. As compared to other polymer types capacitors cover a wider range of voltages and capacitance & voltage values. The voltage ranges from 2.5 to 100V whereas capacitances range from 3.3 to 2700µF.

Similar to layered polymer capacitors, this type of capacitor includes very low ESR values. Some of these capacitors have 5mΩ of ESR value. These capacitors can also be surface mounted, but like the layered capacitors, these are not quite as compact.

Polymer Tantalum Capacitors

These capacitors use a conductive polymer like the electrolyte and also include a tantalum cathode. The voltage supply of these capacitors ranges from 1.8 to 35V whereas the capacitances range from 2.7 to 680µF. These capacitors also have low ESR values but some of these capacitors will exhibit low ESR values like 5mΩ.

These capacitors are packed within a molded resin case, so these capacitors are the most compact and available in a wide range of sizes on the market.

Polymer Hybrid Aluminum Capacitors

These types of polymer capacitors use a blend of a liquid & conductive polymer as the electrolyte. These capacitors provide low ESR & high conductivity. In the electrolyte, the liquid portion can resist high voltages to provide maximum capacitance ratings because of its huge effective surface region.

These types of polymer capacitors have voltages from 25 to 80V whereas capacitances from 10 to 330µF. As compared to other polymer types of capacitors, these capacitors’ ESR values are higher ranging from 20 to 120mΩ.

Polymer Capacitor Vs Tantalum Capacitor

The difference between polymer capacitors and tantalum capacitors includes the following.

Polymer Capacitor Vs Electrolytic Capacitor

The difference between polymer capacitors and electrolytic capacitors includes the following.

Polymer Capacitor Vs Ceramic Capacitor

The difference between polymer capacitors and ceramic capacitors includes the following.

Advantages

The advantages of polymer capacitors include the following.

• These capacitors offer long life, high capacitance within small packages, high reliability, and other electrical characteristics like the following.
• High ripple current capacity.
• Frequency performance is high like ESR & less impedance.
• Stable operation as compared to changes within bias voltage & temperature.
• The acoustic noise elimination can be created through ceramic capacitors.
• The operating range of temperature is wide-ranging from +125 degrees C or -55 to +105.

Disadvantages

The disadvantages of polymer capacitors include the following.

• These capacitors have a high leakage current.
• High temperature and high humidity.

Applications

The applications of polymer capacitors include the following.

• Polymer capacitors can frequently be found on computer motherboards, particularly on server motherboards.
• These capacitors are helpful in stabilizing the voltage in a sensitive circuit from a power source to reduce power noise.
• These can be used for signal decoupling & power bypass and to reduce power noise & signal noise generated by the device which can be transferred to the power source to affect other devices which are connected to that power source.
• Polymer capacitors are used where a large ripple current is allowed because of low ESR like switched DC-DC converters, Buck-Boost converters, etc.
• A capacitor with less ESR is preferable to enhance power efficiency & safety in overheating & overloading cases.

Know more about Decoupling Capacitor.

Thus, this is all about an overview of polymer capacitors, working, types, differences, and their applications. Failure of polymer capacitor reduces tenfold once the temperature of this component is decreased to 20 °C. So the maximum expected lifetime mainly changes based on different vendors in between 13 to 15 years. The characteristics of polymer capacitors include equivalent series resistance, lifetime, reliability, failure modes, polarization, voltage rating, and capacitance range. Here is a question for you, are polymer capacitors polarized?