A polymer capacitor is a capacitor that utilizes solid polymer as an electrolyte. They have various superior qualities like lower losses, longer lifetime than electrolytic capacitors, and safer failure mode. They use solid polymers instead of gel or liquid polymers because they are commonly used in electrolytic capacitors. Using solid electrolytes is to avoid the drying up of electrolytic material. When the electrolyte dries up, it reduces the lifetime of a capacitor, which is why electrolytic capacitors have to reduce lifetimes. You will find various polymers capacitors, including aluminum polymer capacitors, conductive polymer capacitors, and polymerized organic semiconductors.
Why are Polymer Capacitors Important?
As mentioned, polymer capacitors use a solid polymer as their electrolyte and have increased lifetime and other superior qualities. In most cases, polymer capacitors can also be used as replacements for electrolytic capacitors, but you have to be careful not to exceed the maximum voltage. The maximum rated voltage given to polymer capacitors is lower than that of the electrolytic capacitors, commonly up to 35 Volts; however, some polymers are designed to operate at a maximum voltage of 100 volts DC.
The qualities that polymer capacitors have superior to the electrolytic capacitors include:
- Higher maximum working temperature
- Increased working lifetime
- Lower equivalent series resistance (ESR)
- Safer failure mode
- Better stability
However, the downside to these capacitors could be the lower maximum voltage rating, lower capacitance, and higher cost compared to the electrolytic costs. These capacitors have been used for decades since they were created in the 1880s. Since that time, they have been used in various applications that include computer graphic accelerator cards and server motherboards.
Construction of Polymer Capacitors
The polymer capacitors are constructed by taking the two aluminium foils and putting the electrolytic material between those two foils. This assembly is achieved by rolling them up in a cylindrical shape. After the rolling, electrodes are added, and the whole thing is closed in an aluminium casing. Solid polymer capacitors are not the kind of components that can be replaced in a device; therefore, they are made using SMT. This allows the capacitors to take less space on the printed circuit boards; however, it can be harder to unsolder later on, but that won’t be a problem if any replacements are not needed.
Ordinary electrolytic capacitors have vented casings that allow the case to break in when excess gases are collected inside and released, which is a safer way to prevent accidents or explosions. There is no need for such vented casing in polymer capacitors as no pressure build-ups occur in case of failure.
Applications of Polymer Capacitors
- As polymer capacitors have low ESR, they are used in applications that allow a large ripple current. For example, a switched DC converter allows for ripple current. Other great examples include boosters and buck, boost, and buck-boost, which can keep the voltage at the capacitor constant but produce a high ripple current. A capacitor with low ESR is used in such situations, improves efficiency, and reduces the risk of overheating and overloading.
- The solid polymer can effectively smoothen out the voltage that comes from a power source to a circuit which reduces the power noise.
- They are used for bypassing and decoupling for reducing noise generated from devices.
- Polymer capacitors can also be used on computer motherboards.
