- Capacitors are temporary electrical storage device used in many electrical and electronic devices. Most capacitors are named according to dielectric material used in its construction, example mica, ceramic, Mylar, glass, tantalum, etc. Capacitors have different types which we shall discuss in this article.
In this article, we shall discuss:
- Fixed Capacitors
- Types of fixed capacitors
- Types of ceramics capacitors
- Types of mica capacitors
- Types of film capacitors
- Types of electrolytic capacitors
- Types of super capacitors
- Variable capacitors
- Types of variable capacitors
There are many ways to classify a capacitor; it can be by its working voltage, dielectric material used, by its capacity, by its applications, etc.
The most fundamental types of capacitors are:
This capacitor has a fixed value of capacitance that cannot be altered or change by any means.
Fixed Capacitors have many types; they include:
- Super Capacitor
Ceramic Capacitors, also known as Disc Capacitors are the most popular and widely used non-polarized capacitor in electronic devices. It is small, cheap and contains ceramic dielectric. They are made by coating two sides of a little ceramic disc with silver which are then placed together to make a capacitor.
They are commonly used when large charge storage and small size is required. Also, they are suitable for high frequency applications. Its tolerances range from ±5 to ±100%, while its capacitances range from 1 pF to 2.2 µF, with maximum voltages rating from 3 V to 6 kV. Ceramics capacitor has two types:
- Class 1 ceramics capacitor: They are usually used in resonant circuits due to their high stability and loss. They have low permittivity and they have a linear temperature coefficient that is why they are used in applications like filters and oscillator circuits.
- Class 2 ceramics capacitor: They are usually used in coupling circuits, filters, buffers and by-pass systems due to their high efficiency in terms of volume. Unlike the class 1 ceramics capacitor, they have non-linear temperature coefficient, poor stability and poor accuracy.
- Class 3 ceramics capacitor: They have higher permittivity and better volumetric efficiency but have poor accuracy and stability.
These capacitors are used in devices where high accuracy and low capacitance value are required. They are stable, reliable and high precision capacitors which are available from low to high voltages. There are two types of mica capacitors, they include:
- Silvered Mica Capacitors
- Stacked Mica Capacitors
Silvered mica capacitor
In silvered mica capacitor, the mica sheet is directly coated with silver. This can be done by using screening technique.
Stacked mica capacitors
These capacitors are constructed by placing thin mica sheets over another mica sheet. It is separated by using thin metal sheets of aluminum or copper. The metal sheets acts as electrodes.
After that, it is then sealed (enclosed) in a plastic container in order to protect it from any moisture and mechanical damage.
This type of capacitor uses paper as its dielectric to store electric charge. It is made of paper sheets by placing an aluminum sheet between each paper sheet. Thereafter, they are rolled together in the form of a cylinder and a wire is attached to each end of the aluminum sheets.
The total cylinder is then coated with wax to shield it from moisture. Paper capacitors are used in high voltage and high current applications.
They are fixed capacitor whose dielectric material is glass. They are ultra-reliable and ultra-stable capacitor which is resistant to nuclear radiation. They have stability than silver mica capacitor and less cheap than ceramic capacitor.
Film capacitors also known as plastic film capacitors are non-polarized capacitors that use plastic film as the dielectric. They are commonly used in applications where low loss and high insulation resistance is needed. In films capacitor the dielectric used are Polypropylene (PP), Polyester (PET), Polyphenylene sulfide (PPS), Polyethylene naphthalate (PEN), and Polytetrafluoroethylene or Teflon (PTFE). They are used in filters, peak voltage detectors and for AC applications.
There are two main formats for the construction of plastic film capacitors:
- Film foil capacitors
- Metalized film capacitors
The film foil capacitor is made by placing plastic sheet between two aluminium sheets. Each foil covered with a thin metal foil like aluminium which forms the electrodes. They are then rolled in the form of a cylinder and wire leads are connected to both ends of aluminium sheets.
Metalized film capacitors
Metalized film capacitors are made the same way a film foil capacitors are made. The difference between film foil capacitor and metalized film capacitors is the plastic sheet is directly coated with aluminium.
Types of Plastic Film Capacitors.
- Polyester ( Mylar) Capacitors-This is also a very popular non-polarized capacitor that is reliable, cheap, and has low leakage current but poor temperature stability. Capacitances range from 0.001 to 10 µF, with voltages ratings from 50 to 600 V and its operating temperature is up to 125°C. The limitation of polyester capacitor is, it has higher losses with increasing frequency and temperature.
- Polypropylene Film capacitors– This is the most popular film capacitor. It is used in AC power applications like motors or power factor correction. The limitation of this capacitor is, It has a maximum operating temperature of 105C, can be easily damaged by over voltage and it has low permittivity.
- Polyethylene naphthalate – It is used mainly for non-critical filtering, coupling and decoupling due to temperature dependencies which are not relevant in the circuit. They have better stability at high temperature than mylar capacitors.
- Polyphenylene Sulfide– It is costly than Polypropylene capacitors and Its operating temperature is up to 270°C.
- Polytetrafluoroethylene-It is the most costly of all film capacitors and has an operating temperature of 250°C.
- Polycarbonate – It can withstand full voltage at higher temperature, has very high insulation resistance and has an operating temperature within -55°C to +125°C.
- Polystyrene– It has good thermal stability, low distortion and high insulation. Its high working voltage is up to 3000 V that is why it is used in circuits where operating voltages are very high like power supply circuits, valve amplifiers,etc.
- Polyamide film – They have high insulation resistance and good stability. Its operating temperature is 200°C.
- Polyimide– It has the highest dielectric strength of all the plastic film dielectric.
Electrolytic Capacitors uses electrolyte as one of its electrodes. These are capacitors that have polarity (polarized) on it, that is, the negative and positive terminal is indicated on its body. This polarity must be adhered to, in order to avoid damage of the capacitor. It can be concluded that electrolytic capacity can only be used only on DC circuit applications. Another way, an electrolytic capacitor can get damaged is through over voltage and over temperature that is why they are labeled with following:
- Capacitance value.
- Maximum voltage.
- Maximum temperature.
They are mainly used when high charge storage in small volume is needed.
Electrolytic Capacitor is of three types, they are:
- Aluminium electrolytic capacitors – Aluminium is the dielectric material in this capacitor.
- Tantalum electrolytic capacitors – Tantalum pent oxide is the dielectric material in this capacitor.
- Niobium – Niobium pent oxide is the dielectric material in this capacitor.
Their capacitance is measured in micro Farad
Super capacitor is an electronic that can store huge amount of electric charge. They are also known as ultra –capacitors. They store large electric charge than any other conventional capacitors.
Super capacitor has three types:
- Double-layer capacitors: These capacitors stores charges electrostatically.
- Pseudo capacitors: These capacitors stores charge electrochemically.
- Hybrid capacitors: These capacitors store charge electrostatically and electrochemically.
Just like variable resistors, variable capacitors are capacitors whose capacitance value can be varied or changed either mechanically or electronically. These capacitors are mostly used in radio for tuning and impedance matching in antennas. There two major types of variable capacitor:
- Tuning Capacitor– It is usually used in the tuning of an oscillator circuit in a radio.
- Trimmer Capacitor– It is usually used for one time oscillator circuit internal adjustment.