What is meant by switched capacitors

Is it possible to connect two different capacitors in parallel. Different types of capacitor connections

Content:

In electronic and radio circuits, parallel and serial connection capacitors. In the first case the connection is carried out without common nodes, and in the second embodiment all elements are combined into two nodes and not connected to other nodes, unless this is provided in advance by the scheme.

Serial connection

Connected in series, two or more capacitors are connected to a common circuit in such a way that each previous capacitor is connected to the next capacitor at only one common point. The current (i), which charges the series connection of the capacitors, has the same value for each element, since it only flows in the only possible way. This position is confirmed by the formula: i \ u003d i c1 \ u003d i c2 \ u003d i c3 \ u003d i c4.

In connection with the same value current flows through capacitors connected in series, the amount of charge accumulated by each of them is the same regardless of the capacity. This becomes possible because the charge coming from the lining of the previous capacitor accumulates on the lining of the subsequent circuit element. Therefore, the charging value of the capacitors connected in series looks like this: Q total \ u003d Q 1 \ u003d Q 2 \ u003d Q 3.

If one considers three capacitors C 1, C 2 and C 3 connected in series, it turns out that the middle capacitor C 2 is connected to direct current. It turns out that it is electrically isolated from the common circuit. Ultimately, the value of the effective area of ​​the plates is reduced to the area of ​​the plates of the capacitor with the smallest size. The complete filling of the plates with electrical charge makes it impossible to continue the passage of current. As a result, the current will stop moving in the entire circuit or all other capacitors will stop charging.

The total distance between the panels in series is the sum of the distances between the panels of each element. As a result of the connection in a series circuit becomes a single large capacitor, the area of ​​the plates corresponds to the plates of the element with a minimum capacitance. The distance between the plates is equal to the sum of all the distances available in the circuit.

The voltage drop across each capacitor is different depending on the capacitance. This position is determined by the formula: C \ u003d Q / V, where the capacitance is inversely proportional to the voltage. Thus, as the capacitance of the capacitor decreases, a higher voltage falls on it. The total capacity of all capacitors is calculated according to the formula: 1 / C total \ u003d 1 / C 1 + 1 / C 2 + 1 / C 3.

The main feature of such a scheme is the passage of electrical energy only in one direction. Therefore, the current value is the same in each capacitor. Each frequency converter in a series circuit stores the same amount of energy regardless of capacity. That is, the capacity can be reproduced based on the energy present in the adjacent drive.

Online calculator for calculating the capacitance of capacitors connected in series.

Mixed connection


Parallel capacitor connection

A connection in which the capacitors are connected to one another by two contacts is considered a parallel connection. In this way, several elements can be connected at the same time.


This type of connection allows you to form a single capacitor of large dimensions, the area of ​​which is equal to the sum of the areas of the plates of each individual capacitor. Due to the fact that it is in direct proportion to the area of ​​the plates, the total capacitance is the total number of all capacitor capacitors connected in parallel. That is, C total \ u003d C 1 + C 2 + C 3.

Since the potential difference only occurs at two points, the same voltage drops across all capacitors connected in parallel. The current strength in each of them differs depending on the capacity and voltage value. So consistent and parallel used in different patterns, you can adjust different parameters in specific areas. This will get the necessary results of the whole system as a whole.

Many electronics enthusiasts who are assembling a homemade device ask themselves the question, "How do capacitors connect?"

It seems why this is necessary, because when on concept it indicates that a 47 microfarad capacitor should be installed at this point in the circuit, which means we should take it and set it. But you have to admit that in the workshop, even an avid electronics technician may not have a capacitor of the required nominal value!

A similar situation can arise when repairing a device. For example, an electrolytic capacitor with a capacity of 1000 microfarads is needed and only two or three of 470 microfarads are available. Set 470 microfarads instead of 1000? No, that is not always permissible. So what should be done? Go several dozen of kilometers to the radio market and buy the missing part?

How do I get out of this situation? You can connect multiple capacitors and thus get the capacitance we need. There are two ways to connect capacitors in electronics: parallel and consequent.

In reality it looks like this:


Parallel connection


Schematic diagram of the parallel connection


Serial connection

Schematic representation of a serial connection

You can also combine a parallel and a serial connection. In practice, however, this hardly makes sense.

How do you calculate the total capacitance of the connected capacitors?

A few simple formulas will help us with this. Don't hesitate if you are into electronics, sooner or later these simple formulas will help you.

Total capacitance of the capacitors connected in parallel:

C 1 - capacity of the first;

C 2 - the capacity of the second;

C 3 - the capacity of the third;

C N - capacity NCapacitor;

C total - the total capacitance of the compound capacitor.

As you can see, all you have to do is add when the tank is connected in parallel!

Danger! All calculations must be done in one unit. When we do calculations in microfarads, you need to specify the capacitance C 1, C 2 in microfarads. The result is also obtained in microfarads. This rule should be observed, otherwise errors cannot be avoided!

To avoid mistakes when converting microfarads to picofarads and nanofarads to microfarads, it is necessary to know a brief summary of the numerical values. The table will help you with that too. It lists the prefixes that are used for a short record and the factors that can be used for recounting. Read more about it.

The capacitance of two capacitors connected in series can be calculated using another formula. It gets a little more complicated:

Danger! This formula only applies to two capacitors! If there are more, a different formula will be needed. It is more confused and, in fact, not always useful.

Or the same, but more clearly:

If you do several calculations, you will find that with a serial connection, the resulting capacity is always less than the smallest in that chain. What does this mean? This means that when capacitors are connected in series with capacitance of 5, 100 and 35 picofarads, the total capacitance will be less than 5.

In the event that capacitors of the same capacitance are used for the serial connection, this bulky formula is magically simplified and takes the form:

Here instead of the letter M. Enter the number of capacitors and C 1 - its capacity.

It is also worth remembering a simple rule:

If two capacitors with the same capacitance are connected in series, the resulting capacitance will be half the capacitance of each of them.

So if you connect two capacitors in series, each of which has a capacity of 10 nanofarads, the result is 5 nanofarads.

We will not let the words go by the wind, but rather check the capacitor by measuring the capacitance and in practice confirm the correctness of the formulas shown here.

Take two film capacitors. One for 15 nanofarads (0.015 microfarads) and the other for 10 nanofarads (0.01 microfarads). Now take a multimeter Victor VC9805 + and measure the total capacitance of the two capacitors. Here's what we get (see photo).


Series capacitance measurement

The capacitance of the composite capacitor was 6 nanofarads (0.006 microfarads).

Now we do the same, only for the parallel connection. Check the result with the same tester (see photo).


Parallel capacitance measurement

As you can see, when connected in parallel, the capacitance of two capacitors has developed and is 25 nanofarads (0.025 microfarads).

What else do you need to know to properly connect capacitors?

First of all, don't forget that there is another important parameter, like the rated voltage.

When the capacitors are connected in series, the voltage between them is distributed in inverse proportion to their capacitances. Therefore, it makes sense to use capacitors with a voltage rating equal to that of a capacitor in series that we will connect to.

If capacitors with the same capacitance are used, the voltage will be evenly divided between them.

For electrolytic capacitors.


Series connection of electrolytes

Series circuit diagram

Also don't forget the nominal voltage. With a parallel connection, each of the capacitors involved must have this nominal voltage, as if we were inserting a capacitor into the circuit. That is, if you need to build a capacitor with a nominal voltage of 35 volts and a capacitance of, for example, 200 microfarads into the circuit, then two capacitors of 100 microfarads and 35 volts can be connected in parallel. If at least one of them has a lower voltage rating (say 25 volts) it will soon fail.

It is desirable that the capacitors of the same type are selected for the composite capacitor (film, ceramic, mica, metal paper). It is best if they come from the same batch, as in this case there is little variation in the parameters.

Of course, a mixed (combined) connection is also possible, but in practice this is not the case (which I have not seen). Calculating the capacity for a mixed connection is usually done for those solving physical problems or passing exams :)

If you are seriously interested in electronics, you absolutely have to know how to connect resistors correctly and how to calculate their total resistance!

Electrical capacitors are widely used in electronic devices. They lead in the number of uses in the units of equipment and, according to some criteria, are only in second place after resistances. Capacitors are present in every electronic device and their need for modern electronics is constantly growing. In addition to the wide range, new types will continue to be developed that are characterized by improved electrical and operational properties.

A capacitor is an element of a circuit that consists of conductive electrodes that are isolated from one another by a dielectric.

Capacitors are characterized by capacitance, namely by the ratio of the charge to the potential difference that is transferred by this charge.

In the international SI system per capacity unit is the capacity of the capacitor with an increase in potential of one volt when the charge is sent to a handheld device. This unit is called Farada. It's too big for practical use. Therefore, smaller units of measurement such as picofarad (pF), nanofarad (nF) and microfarad (μF) are commonly used.

Dielectric type groups

Dielectrics are used to isolate the plates from one another. They consist of organic and inorganic materials. Oxide films made of metals are often used as a dielectric.

According to the type of dielectric, the elements are divided into groups:

  • organic
  • inorganic;
  • gaseous;
  • oxide.

Elements with an organic dielectric are made by winding thin ribbons of special paper or foil. Also use a combined dielectric with foil or metallized electrodes. Such elements can be both high voltage (above 1600 V) and low voltage (up to 1600 V).

Inorganic dielectric products use ceramic, mica, glass and glass-ceramic, glass enamel. Their plates consist of a thin metal layer that is deposited on the dielectric by means of metallization. There is high voltage, low voltage and noise rejection.

Compressed gas (Freon, nitrogen, SF6 gas), air or vacuum is used as the gaseous dielectric. Due to the nature of the change in capacity and function, such elements are constant and variable.

The most common elements with a vacuum dielectric. They have large specific capacities (compared to a gaseous dielectric) and a higher dielectric strength. Vacuum dielectric elements have stability of the parameters with temperature changes in the area.

An oscilloscope - the transmitters work on short, medium and long waves with a frequency of up to 30-80 MHz.

Elements with oxide dielectric are:

  • general purpose;
  • launchers;
  • pulse;
  • non-polar;
  • high frequency;
  • noise reduction.

A dielectric is an oxide layer that is deposited electrochemically on the anode.

Legend

Elements are identified by an abbreviated and complete system.

With a reduced system letters and numbers are usedIf the letter indicates the subclass, the number indicates the group depending on the dielectric used. The third element indicates the product type registration number.

With full symbol parameters and properties are specified in the following order:

  • designation symbol of the product;
  • rated voltage of the product;
  • rated capacity of the product;
  • permissible capacity deviation;
  • temperature stability of product capacity;
  • nominal reactive power products.

Face value selection

Capacitors can be connected together in a number of ways.

In practice, it often happens that a limited number of radio components have to be used when assembling a circuit or when replacing a faulty element. It is not always possible to select the elements of the desired nominal value.

In this case, the capacitors must be connected in series and in parallel.

When connected in parallel, their connections the total value is the sum of the capacities individual elements. With this connection scheme, all element skins are connected in groups. One of the outputs of each element is connected to a group and the other output is connected to another group.

There the voltage on all plates is the samebecause all groups are connected to the same power source. In effect, one capacitance is obtained, the total of all capacitances in a given circuit.

To get high capacitance make a parallel capacitor connection.

For example, you need to connect a three-phase motor, single-phase 220 V. A capacity of 135 μF is required for the motor's operating mode. It is very difficult to find, but can be obtained by using a parallel connection of elements at 5, 30 and 100 microfarads. By adding we get the necessary unit of 135 μF.

Capacitor series connection

The series connection of capacitors is used when a capacitance is to be achieved which is smaller than the capacitance of the element. Such elements withstand higher voltages. When the capacitors are connected in series, the reciprocal of the total capacitance is equal to the sum of the reciprocal of the individual elements. In order to obtain the required value, certain capacitors are required, the series connection of which gives the required value.

By series connection is meant cases in which two or more elements are in the form of a chain, each of which is connected to one another at only one point. Why are capacitors placed this way? How I make it right? What do you need to know? What properties does the series connection of capacitors have in practice? What is the formula for the result?

What do you need to know for a proper connection?

Unfortunately, it's not as easy here as it seems. Many beginners think that it is enough to take an element for 49 microfarads and install it (or replace it with an equivalent one), if it is written on the circuit diagram. But the necessary parameters are difficult to choose even in a professional workshop.What if there are no necessary elements? Suppose there is such a situation: a capacitor for 100 microfarads is needed, and there are several parts for 47. It is not always possible to place it. Buying a capacitor on the radio market? Not necessarily. It will be enough to connect a couple of elements. There are two main methods: connecting capacitors in series and in parallel. We'll talk about the first one. However, if we talk about the serial connection of the coil and capacitor, there are no particular problems.

Why do that?

If such manipulations are carried out with them, then the electrical charges on the plates of each element will be the same: KE \ u003d K 1 \ u003d K 2 \ u003d K 3. KE is the final capacitance, K is the value of the capacitor let through. Why so? When the charges come from the power source to the outer plates, the transfer of the value, that is, the value of the element with the smallest parameters, to the inner plates can be carried out. That is, if you use a 3 microfarad capacitor and connect it to 1 microfarad, the end result is 1 microfarad. Of course, a value of 3 μF can be maintained for the first value. The second element cannot miss that much, however, and it cuts off anything above what is required, leaving a large capacitance for the original capacitor. Let's look at what needs to be calculated once the capacitors have been connected in series. Formula

  • OE is the total capacity;
  • N is the voltage;
  • KE - final capacity.

What else do you need to know to properly connect capacitors?

First of all, don't forget that in addition to capacitance, they also have a nominal voltage. Why? When a series connection is made, the voltage is distributed between them in inverse proportion to their capacitances. Therefore, the use of this approach only makes sense in cases where a capacitor can provide the minimum operating parameters required. If elements of the same capacity are used, the voltage will be evenly divided between them. Caution is also required with electrolytic capacitors: Always pay attention to the polarity when working. To ignore this factor, the series connection of capacitors can give a number of undesirable effects. And it is good if everything is limited to just the breakdown of these elements. Keep in mind that capacitors accumulate current, and if something goes wrong, depending on the circuit, a precedent can occur that will cause other components of the circuit to fail.

Series current

Due to the fact that there is only one possible path, all capacitors have a value. In addition, the accumulated amount of charge has the same value everywhere. Capacity doesn't matter. Look at a capacitor series circuit. The right lining of the first is connected to the left of the second, and so on. If more than 1 element is used, some of them will be isolated from the common circuit. Thus, the effective area of ​​the plates becomes smaller and corresponds to the parameters of the smallest capacitor. Which physical phenomenon is this process based on? The fact is that once the capacitor is filled with electrical charge, it stops letting current pass through it. And then it cannot flow along the entire chain. In this case, too, the remaining capacitors cannot be charged.

Voltage drop and total capacity


Each element gradually dissipates the tension. Since the capacitance is inversely proportional, the smaller the drop, the greater the decrease. As already mentioned, capacitors connected in series have the same electrical charge. So if you divide all of the terms by the total, you get an equation that shows the total capacity. The series and parallel connection of capacitors are very different.

Example No. 1

Let's use the formulas given in the article and let's calculate some practical problems. So we have three capacitors. Their capacity is: C1 \ u003d 25 μF, C2 \ u003d 30 μF and C3 \ u003d 20 μF. They are connected in series. It is necessary to find their total capacity. We use the corresponding equation 1 / C: 1 / C1 + 1 / C2 + 1 / C3 \ u003d 1/25 + 1/30 + 1/20 \ u003d 37/300. We translate to microfarads, and the total capacitance of the series capacitor (and the group is considered as one element in this case) is approximately 8.11 μF.

Example No. 2

Let's fix one more issue to consolidate the achievements. There are 100 capacitors. The capacitance of each element is 2 μF. It is necessary to determine their total capacity. You need to multiply their number by the characteristic: 100 * 2 \ u003d 200 μF. The total capacitance of a capacitor connected in series is therefore 200 microfarads. As you can see, nothing complicated.

Conclusion


So we worked out the theoretical aspects, studied the formulas and features of correctly connecting capacitors (one by one), and even solved several problems. I would like to remind readers not to lose sight of the influence of nominal voltage. It is also desirable that elements of the same type are selected (mica, ceramic, metal, foil). Then the series connection of capacitors can bring the greatest benefit.

In this article we will try to uncover the subject of capacitor connection in different ways. From the article on connecting resistors, we know that there is serial, parallel and mixed connection, the same rule applies to this article. A capacitor (from the Latin word "condensare" - "to condense", "to thicken") is a very common electrical device.

These are two conductors (plates) with an insulating material between them. If voltage (U) is applied, an electrical charge (Q) accumulates on the conductors. Its main characteristic is the capacity (C). The capacitor properties are described by the equation Q \ u003d UC, the charge on the plates and the voltage are directly proportional to each other.

Capacitor symbol on the circuit

An alternating voltage is applied to the capacitor. It charges itself with increasing voltage, the electrical charge on the plates increases. As the voltage decreases, the charge on the plates decreases and it is discharged.

It follows that the wires connecting the capacitor to the rest of the circuit will cause electrical current to flow when the voltage across the capacitor changes. It doesn't matter what happens in the dielectric between the conductors. The amperage is equal to the total charge that flows through a wire connected to the capacitor per unit of time. It depends on its capacity and the rate of change of the supply voltage.

The capacitance depends on the properties of the insulation, as well as the size and shape of the conductor. The unit of measurement for capacitor power is farad (F), 1 F \ u003d 1 C / V. In practice, however, capacitance is more often measured in micro (10-6) or pico (10-12) farads.

Basically, capacitors are used to build frequency dependent circuits in order to obtain a strong short electrical pulse where it is necessary to accumulate energy. By changing the properties of the distance between the plates, you can measure the liquid level.

Parallel connection


A parallel connection is a connection in which the connections of all capacitors have two points in common - we refer to them as the input and output of the circuit. All inputs are therefore grouped together at one point and all outputs at another point. The voltages on all capacitors are the same:

A parallel connection involves the distribution of the charge received from the charge source over the plates of several capacitors, which can be described as follows:

Since the voltage on all capacitors is the same, the charges on their plates depend only on the capacitance:

The total capacitance of the parallel capacitor group:

The total capacitance of such a group of capacitors is equal to the sum of the capacitances contained in the circuit.

Capacitor blocks are widely used to increase the performance and stability of power systems in power lines. At the same time, costs for more powerful line elements can be reduced. The stability of the power line, the resistance of the power line to failures and overloads are increased.

Serial connection


The series connection of capacitors takes place one after the other without branching the conductor. The charges are transferred from the voltage source to the plates of the first and the last capacitor.

Due to the electrostatic induction on the inner plates of neighboring capacitors, the charge on the electrically connected plates of neighboring capacitors is balanced, which is why electrical charges of the same magnitude and opposite sign appear on them.

With this connection, the electrical charges on the plates of the individual conders are the same:

Total voltage for the entire circuit:

It is obvious that the voltage between the conductors for each capacitor depends on the accumulated charge and capacitance, i.

The equivalent capacity of a series connection is therefore:

It follows that the reciprocal of the total capacitance is equal to the sum of the reciprocal of the capacities of the individual capacitors:

Mixed connection

A mixed interconnection of capacitors is an interconnection in which series and parallel connections exist at the same time. For a better understanding, let's look at this connection as an example:


The figure shows that two capacitors are connected in series at the top and bottom and two in parallel. You can derive the formula from the above compounds:

The basis of any radio technology is a capacitor, used in a variety of schemes, serving as both a power source and an application, analog signals, data storage, as well as telecommunications for frequency control.