The capacitor is one of the widely used electrical circuit elements in electrical and electronic circuits. In fact, it is hard to imagine any circuit without capacitors.
Depending on the type of dielectric material and the construction of the capacitor, there are various types of capacitor which are used in different applications, like decoupling, timing and wave shaping, filtering, etc. Depending on the different characteristics or the electrical properties of the capacitor, different capacitors are used for different applications.
Fig. 1 Various Types of Capacitors
Here is a list of some of the important specifications or the electrical characteristics of the capacitor.
- Rated Capacitance
- Rated Voltage
- Temperature Coefficient
- Leakage Resistance
- Volumetric Efficiency
- Effective Series Resistance / Dissipation Factor
These electrical characteristics or the specification decides which type of capacitor should be used for a specific application.
Types of Capacitors
There are various types of capacitors that are used in electrical and electronic circuits. But here is the list of widely used capacitor types.
- Electrolytic Capacitors
- Ceramic Capacitors
- Film Capacitors
- Mica Capacitors
- Trimmer Capacitors (Variable Capacitor)
The capacitors can be classified as polarized and non-polarized capacitors. Electrolytic capacitors and supercapacitors are polarized capacitors, while ceramic, film, mica, or trimmer capacitor are non-polarized capacitors.
The electrolytic capacitors are polarized capacitors where the anode or the positive terminal of the plate is made up of metal and through anodization, the oxide layer is created. This oxide layer acts as an insulator. The electrolyte covers the surface of the oxide layer and acts as a cathode or the negative plate of the capacitor. Depending on the type of material used for the electrode, there are three types of electrolytic capacitors.
- Aluminum Electrolytic Capacitor
- Tantalum Electrolytic Capacitor
- Niobium Electrolytic Capacitors
Aluminum Electrolytic Capacitor
Fig. 2 Aluminum Electrolytic Capacitors
In aluminum electrolytic capacitors, the anode or the positive terminal is made up of aluminum. The aluminum oxide acts as a dielectric. And the electrolyte acts as a cathode of the capacitor. Due to the very thin oxide layer, it is possible to achieve very high capacitance in these aluminum capacitors.
Here is the typical characteristics of the Aluminum Electrolytic Capacitor
- Cheaper than other types of capacitor
- Large Capacitance (0.1 µF to 2.2 F)
- Voltage Rating ( 2.5 V to 700V)
- Typical Tolerance (± 10% to 20 %)
- High Effective Series Resistance (ESR)
- High Leakage current
- Lower Lifetime than other types of capacitor (Particularly for wet electrolytic capacitors)
Usage: Since these capacitors are polarized they are typically used in DC applications. They are used in the DC power supply filtering and the de-coupling application.
Fig.3 Tantalum Capacitors
In the tantalum capacitor, the tantalum metal is used as electrode and thin tantalum oxide Is created on top of it, which acts as a dielectric. This tantalum capacitors are available in lead type and as well in the chip form for the surface mounting.
Here is the typical characteristics of the Tantalum Electrolytic Capacitor
- Capacitance Range: 10 nF to 100 mF
- higher Volumetric Efficiency than Aluminum Electrolytic Capacitors
- Rated Voltage: 2V to 500 V
- Tolerance : ± 5% to 20 %
- Lower ESR than Aluminium Capacitors (can withstand higher ripple currents than aluminum capacitors for the same capacitance and voltage rating)
- Very stable over the temperature range and very reliable
- Longer shelf life
- Very sensitive to reverse polarity (Even a small amount of reverse voltage can lead to the destruction of the capacitor)
- Very sensitive to the high voltage spikes
Due to reliability and good volumetric efficiency, the tantalum capacitors are used in applications where good reliability is required and there is a size constrain.
- Sample and Hold Circuits
- Medical Devices
- Power Supply Filtering Circuits in laptops and other compact devices
- Military and Space Applications
Fig. 4 Niobium Oxide Capacitors
Niobium Capacitors are not as popular as tantalum and aluminum capacitors but, in some capacitance, and voltage range they are used over tantalum capacitors because of their lower price.
Fig. 5 Ceramic Capacitors
In a ceramic capacitor, the dielectric material is the ceramic material. They are available in the lead from and the surface mount from. The ceramic capacitors are available in wide capacitance (0.1 pF to 100µF) and the voltage range ( 2V to 50 kV). The ceramic capacitors are non-polarised capacitors and can be connected either way in the circuit.
Depending on the type of dielectric material of ceramic capacitors, there are two types of ceramic capacitors.
- Type- I Ceramic Capacitors
- Type-II Ceramic Capacitors
Class-I Ceramic Capacitors
Class-I ceramic capacitors are used in the circuits where high stability and low losses are required.They are very accurate and provides very stable capacitance over the change in the temperature, biasing voltage or the frequency.
Here is the typical characteristics of the Class-I Ceramic Capacitor
- Good Stability and Reliability
- Low ESR and Low leakage current
- Low tolerance
- Low Volumetric Efficiency (Typically available in low capacitance value)
Usage: Class-I ceramic capacitors are used in high-frequency applications like resonant circuits and oscillators.
Class-II Ceramic Capacitors
Here is the typical characteristics of the Class-II Ceramic Capacitor
- Low Stability and accuracy than Class-I Capacitors
- High Volumetric Efficiency than Class-I Capacitors
- Non-linear change in the capacitance over the operating temperature range
- Change in capacitance with biasing voltage
- Large Tolerance than class-I capacitors
Usage: Class-II ceramic capacitors are used in applications where stability and the accurate value of capacitance are less important. Typically, they are used in DC power supply filtering circuits and for coupling and decoupling in various circuits.
Multilayer Ceramic Capacitors (MLCC)
Fig. 6 Multilayer Ceramic Capacitors (MLCC)
Now a days, the surface mount type multilayer ceramic capacitor or the MLCC is very popular and billions of such capacitors are produced every year. As shown in Fig. 7, MLCCs are made up of alternating layers of metal electrodes and dielectric ceramic.
Fig. 7 Construction of Multilayer Ceramic chip Capacitor (MLCC)
The resulting capacitor basically consists of many smaller capacitors connected in parallel, and that increases the overall capacitance. MLCCs consist of 500 or more such layers. For type-I MLCC, the capacitance is in the range of pF to nF. And they are used in applications where precision and stability are required. The type-II MLCC are available with capacitance up to 100 µF, and they are used in power supply filtering and general-purpose applications.
Fig. 8 Film Capacitors
In the film capacitor, the plastic film is used as a dielectric material. Depending on the different film materials, there are different types of film capacitors. (e.g polypropylene, polyester, and polystyrene)
The film capacitors are used in applications where good reliability and stability are required. In general, the film capacitors have low ESL and ESR or low dissipation factor. They are available in pF to mF capacitance range with a voltage rating range from 10V to 10 kV.
Depending on the film material, different types of film capacitors have different electrical characteristics.
Polypropylene Film Capacitors
Polypropylene film capacitors are one of the widely used type of film capacitors. Here are typical characteristics of Polypropylene film capacitor.
- Low Leakage Current
- Low Dissipation Factor
- Good Temperature Stability
- Can withstand high voltage and high current surges
- Low Volumetric Efficiency
Usage: They are used in the oscillator and the frequency selective circuits where precise capacitance is required. Due to the low leakage current, it is also used in the sample and hold circuits.
In power electronics,they are used for EMI suppression, power factor correction and in the pulse applications.
Polyester Film Capacitors
They have higher volumetric efficiency than polypropylene capacitors but the capacitance is temperature and frequency dependent. They are typically used in the general-purpose applications.
Fig. 9 Supercapacitors
Supercapacitors are also known as ultra-capacitor. It is used to store a large amount of electrical charge. Typically its capacitance ranges from a few Farad to 100s of Farad. And Maximum charge voltage is 2.5 to 2.9V. Sometimes you also find a supercapacitor whose voltage rating is higher. But in such case, two or more capacitors are connected in series internally.
The super capacitors are used to quickly transfer the charge or for fast charge and discharge time.Batteries usually take up to several hours to reach a fully charged state, while supercapacitors can be brought to the same charge state in less than two minutes.
It finds its application in the automotive industry and in low-power applications where a large life cycle and quick recharge are important. (e.g photographic flash and SRAM)
In the Mica capacitor, a silver mica is used as a dielectric material. These capacitors provide good temperature stability and very accurate capacitance. And therefore they are used in RF applications.
Due to the high breakdown voltage, these capacitors are used in high voltage applications. Because of their large size and high cost, now a days these capacitors are replaced by other capacitors.
Fig. 10 Trimmer Capacitor
Trimmer capacitors are variable capacitors. They are used for the initial calibration of equipment during manufacturing or servicing. In this type of capacitor, by changing the distance between the two plates or by changing the overlapping area between the two plates, the capacitance is varied in certain range.
These capacitors are used to initially set oscillator frequency values, latencies, rise and fall times, and other variables in a circuit. There are two types of trimmer capacitors: air trimmer capacitor and ceramic trimmer capacitor.
The minimum capacitance of these capacitors is around 0.5 pF and it can be varied up to 100 pF. These capacitors are available up to the voltage rating of 300V.