Aluminum Electrolytic Capacitors are one of the important components in the capacitor industry that is used in a wide variety of applications both as an SMD or a leaded device. These capacitors are known as the most popular leaded types with values greater than 1 µF, one of the highest capacitance values for a certain volume. Aluminum electrolytic capacitors are polarized capacitors whose anode is made from pure aluminum foil and has an etched surface. The aluminium creates a very thin layer of aluminium oxide through anodization. This thin layer of aluminium oxide acts as the capacitor's dielectric material. Aluminium capacitors have been used for a long time and have become standard components in many designs.
Electrolytic Capacitor Technology
The electrolytic capacitor utilizes electrolyte as one of its plates to accomplish a larger capacitance per unit volume than other types. There are several ways to increase the capacitance:
- Increasing the dielectric constant
- Decreasing the distance between electrodes
- Increasing the electrode surface area
Electrolytic capacitors utilize the high dielectric constant of the aluminium oxide layer that ranges between 7 to 8 on the plate of the capacitor. This is more than other dielectric materials such as mylar which has a constant of around 3, and mica of around 6 to 8.
Additionally, the surface area inside the capacitor is increased by a factor of up to 120, which is accomplished by roughening the surface of the high purity aluminium foil. This is one of the main ways to achieve high capacitance levels.
Construction of Electrolytic Capacitors
To construct this type of capacitor, two thin films of aluminium foils are used in which one layer is covered up by an oxide layer which performs as an insulator. This is why these capacitors are often referred to as aluminium electrolytic capacitors.
A paper sheet soaked with electrolyte is placed between the two thin films, and the films are wound around one another. After that, they are placed in a can. In constructing these capacitors, one of the initial steps is to etch the foils to make them even rougher. This is done to increase their surface area and the capacitance levels in a certain area.
The next step involves making the anode. Therefore, this stage involves forming a thin layer of aluminium oxide onto the anode foil, differentiating it from the cathode. The capacitor element is wound on a winding gadget. The four separate layers: the anode, separator, cathode, and paper separator, are all combined and wound together. The paper separators are essential to prevent the two electrodes from coming in contact with each other and hence short-circuiting.
When the assembly of the capacitors has been wound, it is taped to ensure that it does not unwind.
Properties of Electrolytic Capacitors
Aluminium electrolytic capacitors provide much higher capacitance levels than many other ceramic capacitors. This indicates that because of their high capacitance value, they can be quite small in size. This is a significant benefit for many situations.
These capacitors are known to be polarized, so you can only place them one way round in the circuit. If they are not connected properly, it can lead to severe damage and even an explosion in some cases. Therefore, it is important not to exceed the rated operating voltage. It is always safe to operate them at a lower value than that.
Electrolytic capacitors also have high tolerance levels that rate from -50% to +100%. Despite this, they are still widely used in audio applications.
