When creating electronic circuits, many different elements are used. One of the most used, without which it is almost impossible to do, is resistors. What are they? What types are there? What is their most important parameter? And what features are there with serial and parallel connection?
What is a resistor?
This is what a passive element of an
electric circuit is called
, which provides resistance to current during its course. In large circuits, they are used more often than any other element of electronics. It is important to ensure the bias mode of transistors when used in
amplifier stages. But the most significant function is the control and regulation of voltage and current values in electrical circuits. We will consider later what types they are. The article will focus on the 5 main ones that are most often used, but there may be others. When calculating resistors, it is imperative to evaluate what power is needed.
Want to understand what is needed in a particular case?
How to find out which resistor is needed when creating circuits? Initially, it should be understood that knowledge of the current strength or the value of the load resistance is mandatory. The article will consider two options for influencing the characteristics of the circuit:
1) If nothing is known, then we take a variable resistor and connect it in series with the load. Turn the knob until we have the right voltage. Now, instead of variable resistance, we connect a constant with the necessary parameters. Measure the current that goes after the resistor and multiplies the obtained value with the voltage that is supplied. Then we will know how much and where to serve.
2) It is necessary to know the previously indicated current and load values. To increase the accuracy of the calculation, it is also desirable to know the value of the internal resistance of the power source.
Let's simulate slightly different conditions of action. There is one resistor as a load, Ohm's law and the need to calculate the resistance needed for the circuit. This is a rather interesting point and he deserves to be given attention. Why was this wording chosen? The fact is that people who are just starting to create circuits very often ask such a question. But, alas, the line of reasoning that they follow is a little wrong. To calculate the necessary value with one Ohm's law will not work here. It is necessary to additionally use the formula for calculating the additional resistor: SDB = SN (NIP-NN) / NN = SN (x-1). Let's analyze the formula:
SDB - resistance of the additional resistor;
NIP - power supply voltage;
CH - load resistance;
X = NPC / NN;
NN is the voltage that needs to be obtained at the load.
We use this formula. Assume that with a resistance of 1 ohm, the SDB will be 0.6 ohms. If we put 5 ohms, the final result will be 3.3 ohms. Why is that so? This is due to the fact that the lower the load resistance, the greater the current characteristic in the circuit. In this case, the power source will sink, because it also creates certain interference for the passage of current. And given that the voltage will also fall with this, it turns out that an additional resistor with lower characteristics is needed to obtain the desired voltage. This tension is literally “on the fingers”. It may be difficult to understand what and how, but you try.
Constant resistor
So called devices that are owners of a constant value of resistance. This characteristic of the resistor does not change under the influence of external influences (temperature, flowing current, light, applied voltage) within a reasonable framework. If you understand this, then about all the radio elements we can say that they have internal noise and instability due to outside influence. But usually this is all so insignificant that it is ignored by amateur radio electronics and makes sense only when creating really complex systems that are not even a fact that they are going somewhere now.
Variable resistor
This is the name of the device, the resistance value of which can be changed using a special pen (it can be a slide, button or rotating type). Why is a resistor of this type needed? A good example of the application of this element is the volume control on the sound speakers of a computer or mobile phone.
Tuning resistor
These are called devices whose operating mode changes only occasionally. To adjust the resistance values, it is necessary to twist the slot that has a resistor with a screwdriver. What is it for? They are widely used on printed 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 from semiconductor materials. If it is necessary to react to the presence of visible light, cadmium selenide and cadmium sulfide are used . To record infrared radiation, germanium is used.
Thermistor
This is a special device with which you can measure the temperature of the environment. A thermistor is also used in thermal stabilization circuits for transistor cascades. As you might have guessed, its resistance can change under the influence of temperature. In chicken incubators, greenhouses, production machines - everywhere you can find this resistor. What is it for? So that when a certain temperature limit is reached, heating / cooling systems are turned on.
Power dissipation
This is the energy absorbed by the resistor, which is generated by current and voltage. Due to the fact that it is dispersion that occurs, and not conservation, this device is called passive. Thanks to this, the resistor can be talked about as an active element that can equally work in alternating and
direct current circuits
.Power designation
How to understand what a constant resistor can do? To do this, look at its designation:
- When there are two oblique lines, the dissipation power is 0.125 watts.
- There is one oblique line - the dissipation power is 0.25 watts.
- One horizontal line is 0.5 watts dissipation power.
- One vertical line is 1 watts dissipation power.
- Two vertical lines - dissipation power of 2 watts.
- Two oblique lines that create the Latin letter V are the dissipation power of 5 watts.
Starting from one watt, Roman numerals are used to indicate.
Serial connection
When does it make sense to apply this approach? If you need to get significant resistance, but there are resistors with a low rating, then use a series connection. To evaluate what and how is done in the scheme, you need to summarize their characteristics.
Parallel connection
And where is such an 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 taking a look at this formula (C - resistance):
1 / C total = 1 / C 1 + 1 / C 2 + ... + 1 / C x .
Application
So we understood what a resistor is, why it is needed. The photos posted in the article make it possible to understand how it looks. But I want to pay attention to its use. So, the resistor. Why is it needed in a car? As you know, cars use a significant amount of electronics. Here it is used to control its work. Why do I need a stove resistor in a car? Have you seen the ability to switch and adjust the temperature mode? That's what a heater resistor is for! After all, without it, it would be possible to turn on only predefined settings and that’s it. Now let's think about why we need a resistor for an LED? With it, you can adjust the brightness of its glow. As you might have guessed, if you carefully read the article, the answer to the question of which resistors are needed for LEDs is variable!
Conclusion
As you can see, a resistor is a necessary and useful thing that has wide possibilities of application. Theoretically, you can do without a resistor in the simplest schemes, for a couple of parts, despite the fact that the energy sources will be very accurately selected. But this is unlikely, and in order to achieve the required value of these indicators, it will take a long time to select them. Here, to simplify the process, resistors are also used, because they allow for significant differences in characteristics, opening up the possibility of even multiple changes.