Polymer capacitors are a type of electrolytic capacitor and they are an excellent choice for any design that requires long life, stable capacitance, small size and high reliability. Polymer capacitors include conductive polymers designed with an aluminum layer.
Polymer capacitors offer long-term reliability, lower ESR, a wide range of package options between 2.2 and 470ufand special features such as conductive polymers in place of liquid electrolytes. These capacitors offer very good resistance to voltage and temperature bias effects as well as good aging characteristics.
Concept of Polymer Capacitors
Polymer capacitors are capacitors that use a solid polymer like an electrolyte are called polymer capacitors. These capacitors will replace electrolytic capacitors in most cases as long as the maximum rated voltage is not exceeded.
These capacitors are typically available in voltages as low as 35 V compared to regular electrolytic capacitors, which offer many superior qualities compared to electrolytic capacitors, such as lower losses, longer service life, and failure mode re-safety.
Construction of Polymer Capacitors
The construction of a polymer capacitor may be accomplished by sandwiching a spacer containing an electrolyte between two terminals (e.g., anode and cathode), wherein the anode is made of aluminum foil and the cathode is made of a conductive polymer. The assembly of the capacitor can then be rolled into a cylindrical shape, including the electrodes, and finally the entire assembly is encapsulated in an aluminum housing.
Since these capacitors are not considered to be components that can be replaced within a device, they are typically manufactured using surface mount technology (SMT), This therefore allows them to take up less space on the printed circuit board (PCB).
The case of an ordinary electrolytic capacitor opens by means of a pre-scored surface, which breaks up under high pressure and vents the gases formed in the case in such a way as to be safe from explosion in case of overheating. Usually, there are no such vents or scratches on these capacitors because there is no significant increase in force in the event of breakdown.
How Polymer Capacitors Work
The work of polymer capacitors can be accomplished through the use of conductive polymers like electrolytes, which use a solid polymer electrolyte instead of the gel or liquid electrolyte found in ordinary electrolytic capacitors.
Thus, by using a solid electrolyte, electrolyte drying can be avoided altogether, bearing in mind that such drying is one of the main factors limiting the life of ordinary electrolytic capacitors.
Types of Polymer Capacitors
There are different types of polymer capacitors available, including laminated polymer, wound polymer, polymer tantalum and polymer hybrid aluminum capacitors, each of which is described below.
1、Layered Polymer Aluminum Capacitors
These capacitors use a conductive polymer as the electrolyte. Depending on the particular model, these capacitors are supplied at voltages ranging from 2 to 25 v. Layered polymer aluminum capacitors provide capacitance ranging from2.2 to 560 uf, and are primarily characterized by a very low ESR (Equivalent Electrodynamic Restrictive Ratio). Some polymer capacitors have low ESR values such as 3mΩ.
Layered polymer aluminum capacitors are packaged in molded resin-like compact SMT devices. As a result, these capacitors are used in handheld electronic devices, otherwise other applications require a thin capacitor that will not interfere through a nearby heat sink.
2、Wire-wound Polymer Aluminum Capacitors
Wire-wound polymer aluminum capacitors rely heavily on aluminum and conductive polymers, but they have a wound foil construction, Wire-wound polymer aluminum capacitors cover a wider range of voltages as well as capacitance and voltage values than other polymer type capacitors. The voltage range is from 2.5 to 100v while the capacitance range is from 3.3 to 2700uF.
Similar to layered polymer aluminum capacitors, this type of capacitor has a very low ESR value, some of which have an ESR value of 5 m2. These capacitors can also be surface mounted, but like layered capacitors, they are not as compact.
3、Polymer Tantalum Capacitors
Polymer tantalum capacitors use a conductive polymer like an electrolyte and also include a tantalum cathode. These capacitors have a voltage range of 1.8 to 35 V and a capacitance range of 2.7 to 680 uf. These capacitors also have a Low ESR value, but some of them will exhibit a low ESR value of, for example, 5 mΩ.
Polymer tantalum capacitors are encapsulated in molded resin cases, making these capacitors the most compact on the market and available in a variety of sizes.
4、Polymer Hybrid Aluminum Capacitors
These types of polymer capacitors use a mixture of liquid and conductive polymer as the electrolyte to provide low ESR and high conductivity. in the electrolyte, the liquid portion can resist high voltages to provide maximum capacitance ratings due to its large effective surface area, the Polymer hybrid aluminum capacitors are available in voltages from 25 to 80 V and capacitances from 10 to 330 pF. The capacitors have higher ESR values from 20 to 120 mΩ. compared to other polymer type capacitors.
Difference between Polymer Capacitors and Tantalum Capacitors
The differences between polymer and tantalum capacitors include the following.
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Polymer Capacitors |
Tantalum Capacitor |
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Polymer capacitors are made of plastic. |
Tantalum capacitors made of metal |
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Having a low voltage rating |
With high rated voltage |
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The electrolyte used is a conductive polymer |
The electrolyte used is solid manganese dioxide |
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The dielectric material used is aluminum oxide |
The dielectric material used is an oxide layer of tantalum pentoxide |
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Once the temperature rises, the voltage rating will increase |
Once the temperature rises, the rated voltage will Decrease |
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The capacitor has a liquid electrolyte and a solid cathode |
The capacitor has a solid electrolyte and a solid anode. |
Differences between polymer and electrolytic capacitors
The differences between polymer and electrolytic capacitors include the following.
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Polymer Capacitors |
Electrolytic Capacitor
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Polymer capacitors with capacitance ranging from 10μF to 1mF |
Has a large capacitance, typically ranging from 1μF to 47mF |
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Capacitors rated up to 35V
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Capacitors are rated for several hundred DC volts |
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In this type of capacitor, the anode is made of aluminum foil and the cathode is made of a conductive polymer |
The capacitor is made of two aluminum foil films
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These capacitors are used to stabilize the voltage from the power supply to the sensitive circuits to reduce power supply noise
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Applications for electrolytic capacitors include. reduction of voltage fluctuations within filtering devices input and output smoothing to filters, decoupling and noise filtering within power supplies and signal coupling between amplifier stages. |
Differences between polymer and ceramic capacitors
The differences between polymer and ceramic capacitors include the following.
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Polymer Capacitors |
Ceramic Capacitor |
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Provides safer failure modes, longer service life, better stability, etc. |
Provides low loss and high stability for resonant circuit applications |
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These capacitors have a lower ESR compared to other electrolytic capacitors |
Very low ESR range from 0.01 to 0.1 ohms |
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Its physical dimensions are 7.3 x 4.3 mm |
Very small physical dimensions, e.g.0.4mm x 0.2mm |
Advantages and Disadvantages of Polymer Capacitors
Advantages of polymer capacitors include the following.
-Long life, high capacitance in a small package, high reliability and other electrical characteristics
-High ripple current capacity.
-Frequency performance as high as ESR with lower impedance.
-Stable operation compared to changes in bias voltage and temperature
-Ceramic capacitors can be used to eliminate noise. Wide range of operating temperatures
Disadvantages of polymer capacitors include the following.
-High leakage current.
-High temperature and high humidity
Polymer Capacitor Applications
Applications for polymer capacitors include the following.
-Often found on computer motherboards, especially server motherboards.
-Helps stabilize the voltage in sensitive circuits from the power supply to reduce power supply sound.
-Can be used for signal decoupling and power bypass, and to reduce power supply noise and signal noise generated by equipment that can be transferred to the power supply and affect other equipment connected to that power supply.
-Used where large ripple currents are allowed due to low ESR, such as switching Dc-Dc converters, Buck-Boost converters, etc.
-Capacitors with lower ESR are better suited to improve power supply efficiency and safety in overheating and overload situations.
Conclusion
Above is the introduction of polymer capacitor construction, types and application characteristics and other related content. it should be noted that once the temperature of the polymer capacitor is reduced to 20 ° c ° c, the failure of the polymer capacitor will be reduced by ten times. In addition, the characteristics of polymer capacitors include factors such as equivalent series resistance, life, reliability failure modes, polarization, rated voltage, and capacitance range, so it is important to consider all of these factors when purchasing.
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