Capacitor: device, principle of operation, application

Definition

The word condenser comes from the Latin condensatio, which translates to accumulation. In physics, this term is used to describe a whole niche of electrical products, the purpose of which is to work as an energy storage device. The amount of accumulated energy depends on the capacity and the square of the voltage on its plates, divided by 2. In this case, the current flows through it only during the charging process. But first things first.

E = (CU²)/2

Simply put, a capacitor is a device capable of storing energy in electric field

Principle of operation

Now that we know how this element is indicated in the diagrams, we need to consider the principle of operation of the capacitor. When the capacitor plates are connected to a power source, electric charges from the positive and negative terminals of the MT rush to the plates, accumulating on them.

The electric current is interrupted after the capacitor is charged to the rated capacity, since there is a dielectric layer between the plates, it cannot flow constantly. When the power supply is turned off, charges will remain on the capacitor, which means that the voltage will remain at its terminals.

The charges accumulated on each of the plates are opposite. Accordingly, the plate that was connected to the positive terminal of the power source is positively charged, and the one that is negatively charged. The principle of operation of this product is based on the attraction of unlike charges in an electrical circuit.

In simple words, the capacitor will store the energy that was transferred from the power source - this is its purpose. However, in practice there are various losses and leaks.

Interesting! The Leiden Bank is the prototype of modern capacitors, born in 1745. This device was capable of storing energy and extracting sparks when its plates were closed. You can see the appearance and construction below.

And in the figure below you can see the design of the simplest flat capacitor - two plates separated by a dielectric:

Since the capacitance is directly proportional to the area of ​​the plates and inversely proportional to the distance between them, in order to increase the capacitance, engineers have developed a number of other forms of capacitors. For example, plates rolled into a spiral - so their area became many times larger with the same overall dimensions, as well as cylindrical and spherical solutions.

One of the laws of commutation states that the voltage across the capacitor plates cannot change abruptly, which is illustrated in the following miniature.

Views

Capacitors can be classified according to various criteria.

By constancy of capacity:

• Permanent.
• Variables. Their capacity can be changed either manually by the operator (user) of the device, or under the influence of voltage (as in varicaps and variconds).

By polarity of the applied voltage:

• Non-polar - can work in AC circuits.
• Polar - if the voltage is connected with the wrong polarity, it will fail.

Depending on where these components are used, different material options are distinguished:

• Paper and metal-paper capacitors are familiar to many, common in Soviet times in the form of rectangular bricks with markings like "MBGCH". You can see the appearance of this type of capacitor below. They are non-polar.
• Ceramic - they often filter high-frequency interference, and the relative permittivity allows you to make multilayer components with a capacity comparable to electrolytes (expensive), not sensitive to polarity.
• Film - common in the form of brown pads, inexpensive, used everywhere. They are characterized by low leakage current, small capacity, high operating voltage and insensitivity to the polarity of the applied voltage.
• With air dielectric. The best example of such an element is a tuning capacitor of a resonant circuit from a radio receiver, the capacity of such elements is small, but it is convenient to change it.
• Electrolytic - these are elements in the form of barrels; they are most often installed as a filter of network ripples in a power supply unit. The design and principle of operation allow you to get a large capacity with a small size, but over time they can dry out, lose capacity or swell. You can see how these products look in good condition below. A thin layer of metal oxide is used as a dielectric. If the PSU uses capacitors with a dielectric from AL₂O₃ - the so-called "Aluminum electrolytes", then tantalum (Ta₂0₅ - they also belong to electrolytes) capacitors, because they have a lower leakage current, greater resistance to external influences, in contrast to the previous, aluminum ones.
• Polymer - capable of withstanding high impulse currents, working at low temperatures

Main technical characteristics

If you are repairing or developing an electronic device, you will need to select a suitable capacitor to replace the failed one. And for this you need to familiarize yourself with the basic technical characteristics of the capacitor, on which its operation in the electrical circuit depends.

Rated capacity. It characterizes the main purpose of a component - what charge it can store. The main characteristic is measured in farads [F]. However, such a unit of measurement is too large, so fractions are used:

• Millifarads, mF - 0, 001 F (10^-3);
• Microfarads, μF - 0, 000 001 F (10^-6);
• Nanofarads, nF - 0, 000 000 001 F (10^-9);
• Picofarads, pF - 0, 000 000 000 001 F (10^-12).

The rated voltage is the voltage up to which the capacitor can be guaranteed to operate normally. When this value is exceeded, dielectric breakdown is likely to occur. It can be from units of volts (for electrolytes) and up to thousands of volts (film and ceramics). During repairs, this value should not be lower than that of a failed one, higher - you can!

Deviation tolerance - how much the real capacity can differ from the declared nominal. It can reach 20-30%, but there are also high-precision models with a tolerance of up to 1% - for use in chains where special accuracy is required.

Temperature coefficient of capacity - this parameter is important for electrolytes. With aluminum capacitors, with a decrease in temperature, the capacity decreases and the electrical resistivity increases. ESR)

ESR, Equivalent Series Resistance, is also important for electrolytes. In simple terms, the bigger it is, the worse. For swollen conduits, the ESR rises.

In the table below you can see the permissible ESR values ​​for various nominal capacities and voltages.

Where and why are they used?

Still, let's answer the question "what is the capacitor for?" from a practical point of view. To do this, consider several schemes.

Electrolytic capacitors are most widely used as the already mentioned filter of mains ripple in power supplies. The diagram below shows exactly where the electrolyte is installed. The greater the load, the larger the electrolyte capacity is needed to smooth out the pulsations.

The next place where capacitors are used is high and low pass filters. The diagram below shows typical inclusions. Thus, in acoustic systems, bass, mids and high frequencies are distributed through the speakers without the use of active components.

Ballast power supplies are often used to charge small batteries and power low-power devices such as cheap LED bulbs, radios, and others. The film capacitor is installed in series with the supply device, limiting the current due to its reactance - this is the principle of operation of such a simple circuit.

Snubbers are devices designed to protect semiconductor switches and relay contacts from loads arising from switching. In modern pulsed high-frequency power supplies, snubbers from a resistor and a capacitor are used, such way, the main parameters in the circuit are improved and the load on the keys is reduced, as well as the power loss on its heat. The principle of operation of the snubber is to slow down the rising and falling edges of the voltage on the key by using the time constant of the capacitor charge.

Conclusion

We examined what a capacitor is, how it works and what function it performs. For a deeper study, you need to closely familiarize yourself with what types of capacitors are and their practical features of work in various circuits and applications. So, for example, in cases where special accuracy and reliability are required, low-ESR or tantalum electrolytes are used, while there is not much difference in the filter on the rectifier what to put.

Finally, we recommend watching useful videos on the topic of the article:

Also read:

• What are conductors, semiconductors and dielectrics
• What is electrical capacity
• Methods for determining the capacitance of a capacitor