Tension controlled variable resistor, Electronic resistance adjustment. Electronic potentiometer (10+)
Variable voltage resistor
One of the common applications field Transistor It is the use of it as a resistor, the resistance of which depends on the control voltage. It can be necessary to adjust the gain, compression dynamic range Signal or creating blocks simultaneously remotely adjustable resistor variables.
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How to connect a resistor?
Resistor is an element electrical chain, the main property of which is certain active resistance. There are a lot of resistors varieties - constant, variables, varistors, thermistors, etc., as well as the mass of possible inclusion schemes.
In this article, consider the main inclusion schemes and analyze how to connect the resistor.
Serial connection
The connection is sequentially - one of the main schemes for including the resistor. Suppose we need to solder two resistors into a serial connection. In this case:
If you need to connect more resistors, proceed similarly (see Figure). Remember, with a sequential connection, the general resistance of the circuit will be equal to the sum of the resistance included in the resistors.
Parallel connection
A parallel connection is also one of the main schemes for the inclusion of resistors. For parallel connection of two resistors: 
- the first contacts of both resistors sold out between themselves and connect to the power supply plus;
- the second contacts of both resistors sold out between themselves and connect to minus power source.
If you need to connect more resistors, proceed similarly (see Figure). The overall impedance under the parallel compound is in the formula: R1 * R2 * ... * R2 / R1 + R2 + ... + Rn.
Variable resistor
A variable resistor can be connected to the scheme both sequentially and in parallel. Its main feature is the fact that on its case there is a special knob, which can usually rotate with a small screwdriver. Driving a regulator, you can increase or decrease the resistance.
(permanent resistors), and in this part of the article we will talk about, or variable resistors.
Resistors of variable resistance, or variable resistors are radio components whose resistance can change from zero to nominal value. They are used as regulators of amplification, volume controls and timbre in sound reproducing radio equipment, are used to accurate and smooth up different voltages and are divided into potentiometers and strong Resistors.
Potentiometers are used as smooth amplification regulators, volume controls and timbre, serve for smooth adjustment various stresses, as well as used in the tracking systems, in computing and measuring devices, etc.
Potentiometer Called an adjustable resistor having two permanent outputs and one movable. The constant conclusions are located along the edges of the resistor and are connected to the beginning and end of the resistive element forming the general resistance of the potentiometer. The average output is connected to a movable contact, which moves along the surface of the resistive element and allows you to change the resistance value between the average and any extreme output.
The potentiometer is a cylindrical or rectangular housing, inside of which a resistive element is located in the form of an open ring, and a protruding metal axis, which is a potentiometer handle. At the end of the axis, the plane of the current collector (contact brush) has a reliable contact with the resistive element. The reliability of the contact of the brush with the surface of the resistive layer is provided by the pressure of the slider made of spring materials, for example, bronze or steel.
When rotating the handle, the slider moves along the surface of the resistive element, as a result of which the resistance changes between the middle and extreme leads. And if there is a voltage to submit to the extreme conclusions, then the output voltage is obtained between them.
A schematic potentiometer can be represented as shown in the figure below: the extreme conclusions are indicated by numbers 1 and 3, the average is indicated by the number 2.
Depending on the resistive element, the potentiometers are divided into incomparable and wire.
1.1 Improvant.
In inspire potentiometers, the resistive element is made in the form of horseshoe or rectangular Plates of insulating material, on the surface of which a resistive layer is applied, which has a certain ohmic resistance.
Resistors S. ucho-shaped The resistive element has a round shape and rotational movement of the slider with an angle of rotation 230 - 270 °, and resistors with rectangular The resistive element has a rectangular shape and translational movement of the slider. The most popular are SP, OSP, SP3 type resistors. Figure below shows the SP3-4 type potentiometer with a horseshoe resistive element.
The domestic industry was produced by the SPO type potentiometers, in which the resistive element was pressed into the arcuate groove. The case of such a resistor is made of ceramics, and to protect against dust, moisture and mechanical damageAs well as for electrical shielding, the entire resistor is closed with a metal cap.
SPO type potentiometers have a lot of wear resistance, insensitive to overloads and are small, but they have a disadvantage - the complexity of obtaining nonlinear functional characteristics. These resistors still can still be found in the old domestic radio equipment.
1.2. Wire.
IN wire Potentiometers The resistance is created by a high-resistant wire wounded into one layer on the ring-shaped frame, which moves mobile contact for the edge. To obtain a reliable contact between the brush and winding, the contact track is determined, polished, or polished to a depth of 0.25d.
The device and the framework of the frame is determined on the basis of the accuracy class and the law of changing the resistance of the resistor (the law of resistance changes will be said below). Frames are made from the plate, which after winding the wires are folded into the ring, or take the finished ring for which the winding is placed.
For resistors with accuracy not exceeding 10 - 15%, the frames are made from the plate, which, after winding the wires, turn into a ring. Material for the frame is insulating materials, such as Ghetinax, textolite, fiberglass, or metal - aluminum, brass, and the like. Such frames are easy to manufacture, but do not provide accurate geometric sizes.
Frames made of finished rings are made with high accuracy and used mainly for the manufacture of potentiometers. The material for them is plastic, ceramics or metal, but the disadvantage of such frames is the complexity of the winding, as special equipment is required for its winding.
The winding is performed by wires from high-tech alloys electrical resistance, for example, Konstanta, Nichrome or Manganin in enamel isolation. For potentiometers, wires from special alloys based on noble metals, which have reduced oxidation and high wear resistance. The diameter of the wire is determined on the basis of the valid current density.
2. The main parameters of variable resistors.
The main parameters of the resistors are: full (nominal) resistance, form functional characteristic, minimum resistance, rated power, level of rotation noise, wear resistance, parameters characterizing the behavior of the resistor during climatic influences, as well as dimensions, cost, etc. However, when selecting resistors, it most often pay attention to the nominal resistance and less often on the functional characteristic.
2.1. Nominal resistance.
Nominal resistance The resistor is indicated on its housing. According to GOST 10318-74, preferred numbers are 1,0 ; 2,2 ; 3,3 ; 4,7 Om, kiloma or mega.
In foreign resistors, preferred numbers are 1,0 ; 2,0 ; 3,0 ; 5.0 Om, kiloma and mega.
Allowable resistance deviations from the nominal value are mounted within ± 30%.
Full resistance of the resistor is the resistance between the extreme leads 1 and 3.
2.2. Form functional characteristic.
The potentiometers of the same type may differ functional characteristicThe resistance of the resistor between the extreme and middle conclusion is changing according to what law when the resistor handle is rotated. In the form of the functional characteristic, potentiometers are divided into linear and nonlinear: W. linear magnitude Resistance changes in proportion to the movement of the current collector, nonlinear it changes according to a certain law.
There are three basic laws: BUT - linear, B. - logarithmic, IN - back logarithmic (indicative). For example, to adjust the volume in the sound-reproducing equipment, it is necessary that the resistance between the average and extreme output of the resistive element changed return logarithmic law (B). Only in this case, our ear can perceive a uniform increase or decrease in volume.
Or in measuring instruments, for example, generators sound Frequencywhere variable resistors are used as frequency elements, it is also required to change their resistance to logarithmic (B) or return logarithmic law. And if this condition is not executed, the generator scale will be uneven, which makes it difficult to accurately install the frequency.
Resistors S. linear The characteristic (a) is used mainly in voltage divisors as adjusting or trimming.
The dependence of resistance from the angle of rotation of the resistor handle for each law is shown on the chart below.
To obtain the desired functional characteristic, large changes in the potentiometer design are not made. For example, in wire resistors, the winding of the wires lead with a changing step or the frame itself makes a changing width. In inspire potentiometers, change the thickness or composition of the resistive layer.
Unfortunately, adjustable resistors have relatively low reliability and limited service life. Often owners of audio equipment operated for a long timeYou have to hear the roots and cracks from the loudspeaker when the volume control is rotated. The reason for this unpleasant moment is to disrupt the contact of the brush with the conductive layer of the resistive element or the depreciation of the latter. Sliding contact is the most unreliable and vulnerable place of the variable resistor and is one of the main cause of the output of the part.
3. Designation of variable resistors in the schemes.
On the concept schemes Variable resistors are indicated as well as permanent, only an arrow is added to the main symbol pointing in the middle of the case. The arrow indicates the regulation and simultaneously indicates that this is the average output.
Sometimes there are situations where the requirements of the reliability and duration of operation are presented to the variable resistor. In this case, smooth regulation is replaced with a stepped, and the variable resistor is built on the database with several positions. Connect resistors of constant resistance are connected to the switch contacts, which will be turned on in the circuit when turning the switch knob. And in order not to clutter the diagram with a switch with a set of resistors, only a symbol of a variable resistor with a sign indicate step regulation. And if necessary, the number of steps additionally indicate.
To control the volume and timbre, the level of recording in the audio reproducing stereo equipment, to control the frequency in signal generators, etc. Applied dual potentiometerswhose resistance changes simultaneously when turning general axis (engine). In the schemes, the symbols of the resistors included in them are located as close as possible to each other, and the mechanical communication, which ensures the simultaneous movement of the engines, is shown either two solid lines or a single dotted line.
The belonging of the resistors to one dual unit is indicated according to their positional designation in the electrical circuit, where R1.1 is the first diagram of a resistor of a dual variable resistor R1, and R1.2 - Second. If the symbols of the resistors are at a great distance from each other, then the mechanical communication is denoted by segments of the dotted line.
Industry produced dual variables of resistors, in which each resistor can be controlled separately because the axis of one passes inside the tubular axis of the other. In such resistors, there is no mechanical connection that provides simultaneous movement, therefore, it is not shown in the diagrams, and belonging to the dual resistor indicate according to the positional designation in the electrical circuit.
In portable household audio equipment, for example, in receivers, players, etc., often use variable resistors with a built-in switch, which is connected to power to power into the device circuit. In such resistors, the switching mechanism is combined with the axis (handle) of the variable resistor and when the knob is reached, the extreme position affects the contacts.
As a rule, in the circuits of the switch contacts are located near the power supply in the power supply of the feed wire, and the switching of the switch with the resistor is denoted by a dotted line and a point that one of the sides of the rectangle is placed. It is understood that the contacts are closed when driving from a point, and open when moving to it.
4. Strip resistors.
Strong resistors are a type of variables and serve for a single and accurate tuning Radio electronic equipment in the process of its installation, adjustment or repair. As trimmed, both variable resistors of the usual type with a linear functional characteristic, the axis of which is performed "under the slot" and is equipped with a locking device and resistors of a special design with the increased accuracy of the resistance value setting.
In the bulk of its mass, the rapid resistors of the special design make a rectangular shape with flat or ring resistive element. Resistors with flat resistive element ( but) Have a translational movement of the contact brush carried out by a micrometric screw. In resistors with a ring resistive element ( b.) Move the contact brush is carried out by worm transmission.
At large loads, open cylindrical resistor designs are used, for example, PEVR.
On the schematic diagrams, trimming resistors are indicated as well as variables, only instead of the regulatory sign uses a sign of trimmed regulation.
5. Turn on the variables of resistors to the electrical circuit.
IN electrical circuits variable resistors can be used as reostat (adjustable resistor) or as potentiometer (voltage divider). If the current must be adjusted in the electrical circuit, the resistor includes a retake, if the voltage, then include the potentiometer.
When the resistor is turned on reostat Middle and one extreme conclusion. However, such an inclusion is not always preferable, since a random loss of the average contact with a resistive element is possible in the regulatory process, which will entail an unwanted electric circuit breaking and, as a result, a possible way out of the order or electronic device as a whole.
To exclude a random chain rupture, the free output of the resistive element is connected to the movable contact so that the electrical circuit can always be closed when contacting the contact.
In practice, the inclusion of the rheostat is used when the variable resistor wants to be used as an additional or current-limiting resistance.
When the resistor is turned on potentiometer All three conclusions are activated, which allows it to use the voltage divider. Take, for example, a variable resistor R1 with such a nominal resistance that will extinguish almost all power supply voltage coming on the HL1 lamp. When the resistor knob is unscrewed to the extremely top according to the position, the resistance of the resistor between the upper and middle conclusions is minimally and all the power supply voltage enters the lamp, and it glows with complete potassium.
As the resistor handle moves down the resistance between the upper and middle output will increase, and the stress on the lamp will gradually decrease, which will not shine not full of heat. And when the resistance of the resistor reaches maximum valueThe stress on the lamp will fall almost to zero, and it will go out. It is according to this principle that the volume is controlled in the sound-reproducing equipment.
The same stress divider schema can be depicted slightly differently, where the variable resistor is replaced with two permanent R1 and R2.
Well, in principle, and everything I wanted to say about resistors of variable resistance. In the final part, we consider a special type of resistors, the resistance of which is changed under the influence of external electrical and non-electrical factors.
Good luck!
Literature:
V. A. Volga - "Details and nodes of radio-electronic equipment", 1977
V. V. Frolov - "Radiosham's Language", 1988
M. A. ZGUT - "Legend and Radioshem", 1964
A large number of people appeal to radio market to do something with their own hands. the main task Lovers to collect radios and schemes are to create useful items that will benefit not only by yourself, but also others. A variable resistor helps perform repairs or create a device that runs from the electrical network.
The main properties of variable resistors
When a person has a clear idea of \u200b\u200bthe conditional elements of the graphic display in the schemes, then it has the problem of transferring the drawing into reality. It is required to find or acquire individual components of the ready-made scheme. Today there are a large number of shops that sell the necessary details. It is possible to find elements in the old broken radio equipment.
A variable resistor should be present in any scheme. It is found in any electronic devices. This design is a cylinder that includes diametrical opposite conclusions. The resistor creates a limitation of current flow in the chain. If necessary, it will perform resistance that can be measured in Omah. A variable resistor is indicated in the diagram in the form of a rectangle along with two dashes. They are located on the opposite sides inside the rectangle. Thus, a person denotes power in his scheme.
The equipment that is available in almost every home includes resistors with a certain denomination. They are located for a number of E24 and conventionally indicate the range from one to ten.
Varieties of resistors
Today there are a large number of resistors that are found in modern household electrical appliances. The following types can be distinguished:
- Metal resistor lacquered heat-resistant. It can be found in lamp devices that have no power than 0.5 watt. In Soviet equipment, you can find such resistors that have been released in the early 80s. They have different power, which directly depends on the size and dimensions of radio equipment. When there are no schemes legend Power, then it is allowed to use a variable resistor at 0.125 watts.
- Water resistant resistors. In most cases, they are found in lamp electrical appliances, which were produced in 1960. In black and white TV and radiols, these elements are found. Their marking is very similar to the designation of metal resistors. Depending on the rated power, they can have different sizes and dimensions.
Today, the generally accepted marking of resistors, which are divided into different colors are widely used. Thus, it is possible to quickly and easily determine the nominal without using the soldering of the scheme. Thanks to the color label, you can significantly speed up the search for the required resistor. Now the production of such elements for microcircuits is engaged in a large number of foreign and domestic firms.
Main characteristics and parameters of variable resistor
You can select multiple main parameters:
During the design of the presented devices, specific characteristics are used. These parameters relate to devices that work at high frequencies:
Wire variable resistor is considered the main and main element in any electronic equipment. It is used as a discrete component or component to an integrated circuit. It is classified according to the main parameters, such as a way of protection, installation, the nature of resistance changes or production technology.
Classification for general use:
- General purpose.
- Special purpose. They are high-resistant, high-voltage, high-frequency or precision.
Depending on the nature of the resistance change, the following resistors can be distinguished:
- Permanent.
- Variables, with the possibility of adjustment.
- Mounted variables.
If we take into account the method of protecting resistors, then the following structures can be distinguished:
Connecting variable resistor
A large number of people do not know how to connect a variable resistor. These elements often have two connection schemes. Make this work can be a person who is at least a bit dismantled in electronics and dealt with soldering chip.
Technology manufacturing variable resistors
There is a classification that depends on the technology of making resistors. During the production process, different stages and schemes are used. Today you can select the following constructions:
Features of variable resistors in 10 com
Today on the radio markets you can find a large number of elements for the compilation of the scheme. The most popular is the variable resistor 10 com. It can be variable, wire or adjustable. Most of it distinctive feature - Single one-time. This type of resistors is designed to work in an electrical circuit, where there is a permanent or alternating current.
Nominal capacity indicators are 50 volts, and resistance is 15 com. These elements were produced in the middle of the eighties, so today they can be found not only in specialized stores, but also in old radio schemes. A variable resistor 10 kΩ has several functional and possible analogs.
Noise of variable resistor
Even new and reliable resistors at high temperature mode, which is significantly higher than absolute zero, can be the main source of noise. The resistor variable dual is used in the electrical circuit in the chip. The appearance of noise became known from the fundamental fluctuation and dissipation theorem. It is known under the generally accepted name "Theorem Nyvistista".
If the scheme has a resistor Variable joint venture with high resistance indicators, then the person will observe the effective noise voltage. It will have direct proportion to roots from the temperature regime.
Look at the variable resistor ... What do we know about him? Nothing, because we do not even even know the basic parameters of this very spread in electronics radio components. So let's learn more about the parameters of variable and trimming resistors.
To begin with, it is worth noting that variables and trimming resistors are passive components electronic circuits. This means that they consume the energy of the electrical circuit in the process of their work. Passive chain elements also include capacitors, inductors and transformers.
Parameters, with the exception of precision products that are used in military or space technology, they do not have too much:
Nominal resistance. Without a doubt, this is the main parameter. Full resistance can be in the range of dozen Ohm to dozen mega. Why full resistance? This resistance between the extreme fixed conclusions of the resistor is not changed.
With the help of an adjusting slider, we can change the resistance between any of the extreme conclusions and the output of moving contact. The resistance will change from zero and to the impedance of the resistor (or vice versa, depending on the connection). The nominal resistance of the resistor is indicated on its housing using the alphanumeric code (M15M, 15K, etc.)
Scattered or rated power (Resistor Power). In ordinary electronic equipment, variable resistors are used: 0.04; 0.25; 0.5; 1.0; 2.0 watts and more.
It is worth understanding that wire variables, as a rule, more powerful than thin-winged. Yes, it is not wonderful, because the thin conductive film can withstand a much smaller current than the wire. Therefore, the power characteristics can be judged even to judge even appearance "Changer" and its design.
Maximum or limit operating voltage. Everything is clear here. This is the maximum working voltage of the resistor, exceeding which is not worth it. For variable resistors, the maximum voltage corresponds to the row: 5, 10, 25, 50, 100, 150, 200, 250, 350, 500, 750, 1000, 1500, 3000, 8000 volts. Limit voltages of some instances:
SP3-38 (A - D) to the power of 0.125 W - 150 V (for operation in variable and direct current circuits);
SP3-29A. - 1000 V (for operation in the variable and direct current circuits);
SP5-2 - from 100 to 300 V (depending on the modification and nominal resistance).