A capacitor is a passive two-terminal electrical component used to store energy in an electric field. An electrolytic capacitor is a capacitor that uses an oxide film made of aluminum, tantalum or other oxidizable metal as a dielectric.
Almost all the electrolytic capacitors are polarized, which means the voltage of the anode must always be higher than the cathode.
Simple capacitors consist of two plates made of an electrically conducting material such as metal and separated by a non-conducting material or dielectric such as glass, paraffin, mica, oil, paper, tantalum, or air etc.
If a DC electrical potential (voltage) is applied to the plates of a capacitor, the plates will become charged, one positively and one negatively.
If the externally applied voltage is then removed, the plates of the capacitor remain charged, and the presence of the electric charge induces an electrical potential between the plates.
The capacity of the device for storing electric charge is known as capacitance.
It is given by,
C: Capacitance of capacitor in farad
A: Area of any one plate in m2
D: Distance between two plates in m
ε: Permittivity of material = ε0εr
ε0: Absolute permittivity = 8.854X10-12 farad/meter
εr: Relative permittivity
From the equation, we can conclude that, the capacitance can be increased by
- Increasing the area of the plates,
- Decreasing their separation, or
- Changing the dielectric material.
The dielectric constant of a particular dielectric is the measure of the dielectric’s unit capacitance.
Electrolytic Capacitor Symbol
Electrolytic Capacitor Types
- An electrolytic capacitoris a capacitor that uses an electrolyte (an ionic conducting liquid) as one of its plates.
- Because of its potential for large capacitance, this type of capacitor is used extensively in power supply circuits and similar applications.
- Electrolytic capacitors have a larger capacitance than most other capacitor types, typically 1µF to 47mF.
- There is a special type of electrolytic capacitor, called a double-layer capacitor or a supercapacitor, whose capacitance can reach thousands of farads.
- There are two types of electrolytic capacitors.
- Aluminium electrolytic capacitor
- Tantalum electrolytic capacitor
Aluminium Electrolytic Capacitor
The polarized metalized capacitor having aluminium as anode and aluminium oxide as a dielectric material is called Aluminium electrolytic capacitor.
- Aluminum electrolytic capacitors are constructed from two conducting aluminium foils, one of which is coated with an insulating oxide layer, and a paper spacer soaked in electrolyte.
- The foil insulated by the oxide layer is the anode while the liquid electrolyte and the second foil acts as the cathode.
- This stack is then rolled up, fitted with pin connectors and placed in a cylindrical aluminum casing.
- Thus, a capacitor is formed having anode and cathode as Aluminium and electrolyte as dielectric.
- The capacitance of an aluminum electrolytic capacitor is determined by several factors, such as the plate area and the thickness of the electrolyte. This means that a large capacitance capacitor is bulky and large in size.
Tantalum Electrolytic Capacitor
The polarized metalized capacitor having Tantalum as anode and aluminium oxide as a dielectric material is called Tantalum electrolytic capacitor.
- The anode electrode is formed of sintered tantalum grains, with the dielectric electrochemically formed as a thin layer of oxide.
- The cathode electrode is formed either of a liquid electrolyte connecting the outer can or of a chemically deposited semi-conductive layer of manganese dioxide, which is then connected to an external wire lead.
Applications of Electrolytic Capacitors
- They are commonly used as filtering devices in various power supplies to reduce the voltage ripple.
- They are used for coupling signals between amplifier stages.
- Used as electrolytic capacitors as filters in audio amplifiers whose main goal is to reduce mains hum.
- They are used in wave shaping circuits.