With increasing tech advances, capacitors have become essential components in almost every electronic device. They are capable of storing electrical charge, but not for a long period.
By Potshangbam July
Much like a rechargeable battery, capacitors both store and release energy. Capacitors store the potential energy in the electric field, whereas batteries accumulate the energy in the form of chemical energy, which is later changed to electric energy. Capacitors come with features such as easy chargingdischarging capabilities. Today, there is increasing demand for better capacitors for wearables, consumer electronics and for industrial applications.
The importance of capacitors
A capacitor, also known as a condenser, is one of the basic components required for building electronic circuits. The design of a circuit is not complete or it will not function properly without basic components like resistors, inductors, diodes, transistors, etc. The main function of capacitors is to store electrostatic energy in an electric field, and give this energy to the circuit, when necessary. They allow the AC to pass but block the flow of DC to avoid a hazardous breakdown of the circuit.
Though capacitors are tiny, they provide various benefits in electronic circuits.
- They store energy directly onto the plates, which makes the charging/discharging process much faster.
- They are effective in filtering out unwanted frequencies.
- Capacitors can handle power loss efficiently and make power production more economical.
- They are less sensitive to temperature.
- Capacitors discharge current almost instantaneously.
- Capacitors are preferred for AC applications.
- They are capable of handling high voltage applications, and are therefore suitable for high frequency use cases.
- Capacitors have a long life cycle of almost ten to 15 years.
Types of capacitors and their applications
There are several types of capacitors of various constructions, and for different applications and functions. The following are the most common types of capacitors used in electronic circuits.
Film capacitors: These include polyester film, metallised film, polypropylene film, PTE film and polystyrene film capacitors. What differentiates them from one another is the material used as a dielectric.
]The dielectric should be chosen with care, based on its properties. Film capacitors offer several advantages—they are highly reliable and have a long life. They are favoured in high temperature environments.
Film based capacitors are used across automotive electronic units as they exhibit stability during operations at high temperatures and in vibrational environments. The widespread applicability of film capacitors can also be attributed to their high voltage handling capabilities.
Ceramic capacitors: These capacitors have no polarity and a fixed capacitance. They use a ceramic substance as the dielectric material. There are two types of ceramic capacitors that are commonly used—the multi-layer ceramic capacitor (MLCC) and the ceramic disc capacitor. It should be noted that ceramic materials are not good conductors of electricity; therefore electric charges are restricted from flowing through them. The downside of ceramic capacitors is that a minor change in temperature changes their capacitance.
The low inductance of ceramic capacitors makes them suitable for high-frequency applications. They come in small sizes and are used in a range of electronic products, including televisions, mobile phones, digital camcorders, laptops, etc.
Electrolytic capacitors: These can be categorised based on two criteria—the electrode material (aluminium, tantalum or niobium) and the property of the electrolytes (wet, solid, or a wet/solid hybrid). Most electrolytic capacitors have polarity; therefore, with DC voltages it is important to correct the polarity at both ends. On account of their small size and high capacitance, electrolytic capacitors are suitable for use in DC power supply circuits. Their applications are coupling and decoupling. The disadvantage of electrolytic capacitors is their relatively low voltage rating.
Paper capacitors: These are constructed using paper as the dielectric and are capable of storing enough electric charge. The capacitance range for these varies from 0.001 to 2.000 microfarads and the voltage is very high—up to 2000V. This capacitor absorbs moisture from the air, which decreases the insulation resistance of the dielectric. Paper capacitors are used in filtering applications. They can also be used for applications requiring high voltage and high current.
Common problems when the wrong capacitors are used
A bad capacitor can lead to various problems. When a wrong capacitor is used in the circuit, it fails to stabilise the high voltages, which can adversely affect a system, causing it to break down before its expected life time. One should be aware that all capacitors are not made of the same materials. Therefore, using a poor quality capacitor or one with the wrong capacitor rating can have a serious impact on how the circuit operates.
Other issues that erupt with the wrong choice of capacitors are the unnecessary loss of power and unstable circuits. Besides, the incorrect physical size and type of the capacitor may cause problems like unwanted noise, mechanical stress, circuit failure, etc. One should also take into account the thickness of the outer layer of the dielectric of the capacitor. This layer is usually where cracks tend to develop; therefore the thickness of the dielectric matters a lot to increase the mechanical strength as well as the longevity of the products.
Also, when the capacitor is of inferior quality or when the circuit has higher voltage, there are high chances of the chemical insulator leaking out. In such cases, the circuit board is exposed to a mildly reactive compound, which in turn can affect the nearby components and the circuit board’s copper foil.
| Some capacitors available in the market |
| Model: Polypropylene film capacitors; Manufacturer: Panasonic |
| Specifically designed for interference suppression, these capacitors use a flame-retardant plastic case and non-combustible resin; they are fully RoHS compliant. The series has a  safety mechanism to meet UL/CSA and European safety regulation Class X2. Key features
Contact: www.panasonic.eu |
| Model: EPCOS B3277X/Y/Z film capacitor series; Manufacturer: TDK |
The series is suitable for use in DC link circuits, as DC filters, for power factor correction in industrial converters, as well as for power supplies with higher reliability requirements.  These applications include X-ray equipment, LED street lighting, induction hobs and electrical chargers. Key features
Contact: www.tdk-electronics.tdk.com |
| Model: 100nF MLCC ceramic capacitor; Manufacturer: Murata |
The company claims the product is the world’s smallest 100nF MLCC ceramic capacitor for 5G smartphones. It features a maximum capacitance of 0.1μF (100nF). The company has  achieved a mounting surface area that is approximately 50 per cent less and a volume approximately 80 per cent smaller than that of its own conventional products (2552.7 cm size) with a capacitance of 0.1μF. Moreover, the product has a capacity that’s around ten times more than that of other same-sized products (20330.16 cm size) initially mass-produced by the companyContact: www.murata.com |
| Model: Vishay BC Components 257 PRM-SI series; Manufacturer: Vishay Intertechnology |
 This series of miniature snap-in power aluminium electrolytic capacitors enables higher power density designs. The series features a cylindrical aluminium case that is insulated with a blue sleeve. The 257 PRM-SI series of capacitors features rated voltages to 500V in 25 compact case sizes ranging from 22mm x 25mm to 35mm x 60mm. The RoHScompliant devices are also available with 3-pin keyed polarity snap-in terminalsKey features • Case size (D x L in mm): 22 x 25 to 35 x 60 • Capacitance range: 56µF to 3300µF • Tolerance: ± 20 per cent • Useful life at +85°C: 5,000 hoursContact: www.vishay.com |
| Model: KXF series; Manufacturer: United Chemi-Con |
 The KXF series comprises ultra-miniature aluminium electrolytic through-hole capacitors. This series is guaranteed at 15,000~20,000 hours of operation for LED lighting circuits and other long-life, high-voltage power applications. These capacitors are ideal for high- reliability applications such as LEDs, chargers, buck-boost converters, and miniature switching power supplies.
Key features Contact: www.chemi-con.com |
