Resistor: what is it for? How do you know which resistor is needed?

When creating electronic circuits, many different elements are used. One of the most used, without which it is almost impossible to do, are resistors. What are they? What types are there? What is their most important parameter? And what features are there in a serial and parallel connection?

What is a resistor?

This is the name of the passive element of the electrical circuit, which exerts a resistance to the current during its flow. In larger circuits, they are used more often than any other element of electronics. It is important to provide a regime for the displacement of transistors when used in amplifying stages. But the most significant function is the control and regulation of voltage and current values in electrical circuits. We will later consider what their types are. Within the framework of the article, attention will be paid to the 5 main ones that are most often used, but there may be others. When the calculation of the resistors is carried out, it is necessary to evaluate what power is needed.

Do you want to understand what is necessary in a particular case?

How to find out what kind of resistor is needed when creating circuits? Initially, it should be understood that it is mandatory to know the current strength or load resistance value. Within the framework of the article, two variants of influence on the characteristics of the scheme will be considered:

1) If nothing is known, then take the variable resistor and connect it in series with the load. Rotate the regulator until the moment we have the desired voltage. Now instead of the variable resistance we connect a constant with the necessary parameters. Measure the current that goes after the resistor and multiply the resulting value with the voltage that is being supplied. Then we will know how much and where to file.

2) It is necessary to know the previously stated values of current and load. To increase the accuracy of the calculation, it is also desirable to know the value of the internal resistance of the power supply.

Let's simulate a little bit other conditions of action. There is one resistor as a load, Ohm's law and the need to calculate the resistance necessary for the circuit. This is a very interesting moment and it deserves to be given attention. Why was this formulation chosen? The fact is that people who are just starting to create schemes, very often ask such a question. But, alas, the chain of reasoning that they are going on is a bit wrong. Calculate the required value with one Ohm law here will not work. It is necessary to additionally use the formula for calculating the additional resistor: SDB = CH (NIP-HH) / HH = CH (x-1). Let's analyze the formula:

RDB - resistance of the additional resistor;

NPC - power supply voltage;

СН - load resistance;

X = NPC / LV;

HH is the voltage that needs to be obtained on the load.

We use this formula. Let's assume that with a resistance of 1 ohm, the SDB will be 0.6 ohms. If we put 5 ohms, then the final result will be 3.3 ohms. Why is it so? This is because the smaller the value has the load resistance, the greater the current characteristic in the circuit. In this case, the power supply will sink, because it also creates certain interference for the passage of current. And given that this will also reduce the voltage, it turns out that you need an additional resistor with lower characteristics to obtain the desired voltage. This tension is literally "on your fingers." It can be difficult to understand what and how, but you try.

Permanent Resistor

This is the name of devices that have a constant resistance value. This characteristic of the resistor does not change under the influence of external influences (temperature, current flow, light, applied voltage) within reasonable limits. If one understands this, then all radio elements can be said to have internal noises and instabilities due to outside influence. But usually this is all so insignificant that it is ignored by amateur radio electronics and it makes sense only when creating really complex systems, which is not even a fact that they are going somewhere now.

Variable resistor

So called devices whose resistance value can be changed with the help of a special handle (it can be a slider, push-button or rotating type). Why do you need a resistor of this type? A good example of the application of this element is the volume control on the sound columns of a computer or mobile phone.

Constructing resistor

The so-called devices, the mode of operation of which varies only occasionally. To adjust the resistance values, it is necessary to twist the slot with a screwdriver, which has a resistor. What is it for? They were widely used on circuit boards of radio circuits as a current or voltage divider.

Photoresistor

These are special devices that can change the value of their resistance under the influence of light. Photoresistors are made of semiconductor materials. If it is necessary to react to the presence of visible light, then selenide and cadmium sulphide are used. To register infrared radiation, germanium is used.

Thermistor

This is a special device with which you can measure the temperature of the environment. The thermistor is also used in thermal stabilization circuits for transistor cascades. As it was already possible to guess, its resistance can change under the influence of temperature. In incubators for chickens, greenhouses, production devices - everywhere you can find this resistor. What is it for? To ensure that when a certain temperature boundary is reached, the heating / cooling systems are turned on.

Power dissipation

This is the energy absorbed by the resistor, which is formed by current and voltage. Due to the fact that it is scattering, rather than preservation, this device is called passive. Due to this, the resistor can be talked about as an active element, which can equally work in circuits of alternating and direct currents.

Denotation of the power dissipation

How to understand what a permanent resistor can do? For this, it is necessary to look at its designation:

1. When there are two oblique lines, the dissipation power is 0.125 W.
2. There is one oblique line - the power dissipation is 0.25 W.
3. One horizontal line - a power dissipation of 0.5 watts.
4. One vertical line is a power dissipation of 1W.
5. Two vertical lines - a power dissipation of 2 watts.
6. Two oblique lines that create the Latin letter V, - power dissipation of 5 watts.

Starting from a single Watt, roman numerals are used for designation.

Serial connection

When does it make sense to apply this approach? If you need to get significant resistance, but there are resistors with a small value, then use the connection in series. To assess what and how is done in the scheme, then you need to summarize their characteristics.

Parallel connection

And where is this approach necessary? Here, the total resistance of the resistors will be equal to the sum, which is inversely proportional to it. This value is also called "conductivity". It may be a little difficult for you to understand what the author is talking about, so we suggest looking at this formula (C-resistance):

1 / C _total = 1 / C ₁ + 1 / C ₂ + ... + 1 / C _x .

Application

So we realized what a resistor is, why it's needed. The photos posted in the article allow you to understand how it looks. But I want to pay attention to its application. So, the resistor. What is it for in a car? As you know, cars use a significant amount of electronics. That's to control its work and apply it. What is the use of a heater resistor in a car? Did you see the ability to switch and adjust the temperature? That's what the heater resistor is for! After all, without it, it would be possible to include only pre-installed settings and everything. Now let's see why we need a resistor for an LED. With its help you can adjust the brightness of its glow. As you might guess, if you carefully read the article, the answer to the question about what resistors are needed for LEDs are variables!

Conclusion

As you can see, the resistor is a necessary and useful thing, which has wide application possibilities. Theoretically, you can do without a resistor in the simplest schemes, for a couple of details, while the sources of energy will be very accurately chosen. But this is unlikely, and to achieve the necessary value of these indicators will have a long time to select them. Here to simplify the process and apply resistors, because they allow you to conduct significant changes in characteristics, opening the possibility of even a multiple of their change.