Resistor together with capacitor and inductor - the most popular element of electronic and electrical devices.
The resistor as a component, which follows directly from the literal translation of its name suggests, has a certain resistance to current flowing therethrough, whereby in accordance with Ohm's law, it is a falling voltage.
In the process of calculating and analyzing electrical circuits for various purposes classic resistor considered as two-pole, and the resistance is considered to be active. This means that the alternating voltage applied to the resistor, is in phase with the current flowing therethrough.
Key component settings
Basic parameters such as a resistor element different circuits - the resistance and power. The first parameter is so important that in the professional slang of experts resistor is often called resistance. It depends on the capacity of the maximum current at which the resistor is calculated. By increasing the allowable maximum current the power dissipation increases, but at the same time increasing the dimensions of the element.
Resistors are also divided into fixed and variable. Recent equipped with linear or rotary engine, which occurs when you move the change in resistance. In most cases the engine is in the shape of the electrode, which can be removed from (or to which can be applied) voltage. The voltage pickup mode such component is a special name potentiometer.
Modes of using resistor
The specific electrical resistor circuits can operate in three different forms. In the simplest case, it makes a constant current flow circuit resistance. The circuit symbol of the element shown in Figure 1 left.
If necessary, the resistance changes need a variable resistor, which comprise the circuit shown in Figure 1 in the center. For adjusting the resistance operate linear or angular (depending on the specific embodiment) displacement of the engine.
When using a variable resistor in its mode include a potentiometer according to figure 1 on the right and on the electrode engine relieve tension which varies with the engine position. To achieve the linear characteristic through the current regulation resistor itself must at least several times the current discharged from the engine controller.
Resistors special varieties
In solving some problems of circuit use special kinds of resistors.
Their list includes:
- varistors whose resistance depends on the voltage drop;
- thermistors with resistance dependence on temperature;
- photoresistors, the resistance of which depends on the intensity of light falling on them.
varieties of execution
Classic resistor is considered a lead element. Fixed resistors of the variety generally have a cylindrical shape with two axial pin (see. Figure 1) for which it soldered to the electrical circuit.
In those situations, when the resistor is used as a part of circuits that operate at frequencies in the tens or hundreds of MHz, greatly hindering the action is beginning to have an inductance of its conclusions. To overcome this limitation apply leadless or SMD-resistors, are soldered to the circuit board directly on the body.
Variable resistor often manufactured with three independent terminals, figure 3. its use mode (normal variable resistor or potentiometer) define compounds already on the board.
The design of the resistor
Historically, the first were the so-called Wire resistors, the operation member which is wire of a material with high resistivity, wound on a ceramic tubular base. The magnitude of the resistance is adjusted pictures and wire diameter and number of turns and a base diameter. Currently, such structures are preserved only in the components with high power dissipation, as well as in precision laboratory products.
Metal film resistors working element is a film of oxides, and various composite materials.
also quite common carbon resistors, the working layer which is a layer of graphite. To change the resistance of the element graphite layer may be provided with a spiral groove, which changes its width and length increases to a predetermined value.
The necessary mechanical strength and a carbon film resistors attached ink layer. It is necessary to apply the power of information, resistance and accuracy class element. The information is presented as a ring code that can be seen in Figure 2 above, as well as in alphanumeric form.