1、 Resistance, in daily life, we often call it r, the unit is Ohm. If we want to define the resistance, it is the size of the resistance of the conductor to the current. Resistance is a kind of current limiting element. If the conductor has a great blocking effect on the current, we will say that its resistance is high, otherwise, it is called small resistance. But the resistance will not disappear because there is no current passing through the conductor. Resistance is an inherent property of a conductor. Even if there is no current flowing through the conductor, its resistance exists. If you have to add a time limit, it should be ~ 10000 years~~
2、 Classification of resistance
After that, we will know that there are many kinds of resistance
Fixed resistor, variable resistor, special resistor, RT carbon film resistor, RJ metal film resistor, RX winding resistor, sheet resistor, high power resistor and low power resistor.
So, what kind of resistance can play? What are the applications in our daily life? For more information, please see the decomposition below~~~
3、 The function of resistance -- partial voltage
When a resistor and another component such as a bulb are in series in a circuit, the current flowing through the resistor and the bulb is the same, and the sum of the respective voltages of the resistor and the bulb is equal to the total voltage at both ends of the resistance and the bulb as a whole. At this time, the resistance acts as a voltage divider.
4、 The role of resistance 2 -- shunt
When a resistor and another component such as a bulb are in parallel in the circuit, the voltage at both ends of the resistor is the same as the voltage at both ends of the bulb, and the sum of the current flowing through the resistor and the current flowing through the bulb is equal to the total current flowing through the resistor and the bulb. At this time, the resistance acts as a shunt.
5、 The function of resistance 3 -- impedance matching
Impedance matching refers to the process in which the load impedance and the internal impedance of the excitation source adapt to each other in order to obtain the maximum power output in the process of signal transmission. And one of the ways in which it works is by changing the impedance.
6、 The function of resistance 4 -- filtering
In the RC charging and discharging circuit composed of resistance and capacitance in series, the switch S is connected to point B at first, as shown in the figure below, there is no charge on capacitor C, The voltage at both ends of the capacitor is zero, and then the switch S is set at point A. at this time, the power supply starts to charge the capacitor through the resistance R. when the charge at both ends of the capacitor increases to the balance of the circuit, the power supply will no longer charge the capacitor. After that, place the switch s at point B, and the capacitor will start discharging. When the charge at both ends is reduced to zero, the capacitor will not be discharged. Then, the switch s will be placed at point a to start charging In this infinite cycle of charging and discharging, we call the effect of resistance R as filtering effect.
Extended reading
The function of resistance -- zero ohm resistance
In the fixed resistance, there is a special kind of resistance, namely zero ohm resistance. Some children's shoes may not understand, "what's the use of resistance without resistance value? It's a waste of components." It may be so in theory, but in actual production and life, zero ohm resistance has its own production value. Next let's introduce the value of zero ohm resistance.
Zero ohm resistance is often used for the need of EMC countermeasures, but there are several reasons: Zero ohm resistance can facilitate wiring; it can make debugging on PCB more convenient; it is convenient to measure current consumption; it can also play the role of fuse; it can replace wire skipping, dial switch and other welding on the board, in order to prevent users from setting disorderly; It can be used as inductor or or capacitor under high-frequency signal; it can be replaced by zero ohmic resistance when circuit parameters are uncertain, and then change after determination; it can be used to provide a smaller return path when the shortest return path breaks to reduce interference; it can effectively limit the loop current to suppress noise; it can be used as a temperature compensator The zero ohm resistance is so useful. My friends are shocked~~
The function of resistance variable resistance
Variable resistor also known as potentiometer, refers to the resistance value can change, this variability determines the value of its existence. For example, in the analog circuit of some instruments and meters, sometimes there are some uncertain factors. At this time, the variability of potentiometer is needed to adjust it to the best state. There are also some equipment output itself is in constant change, at this time also need potentiometer to achieve.
The function of resistance -- special resistance
Special resistance is made of semiconductor materials, and its resistance value can be changed, but it is different from variable resistance. The resistance value of variable resistance can be adjusted manually, while the resistance value of special resistance depends on the external environmental conditions. For example, the resistance value of the thermistor decreases with the increase of temperature. When applied in the circuit, the temperature can be judged according to the resistance value, which can be used as a thermal sensor; the resistance value of the photosensitive resistance is greatly reduced when there is light, so it can be used as an optical switch in the circuit; The resistance value of varistor varies with the voltage at both ends of the varistor. It can play a protective role in the circuit and protect the circuit from damage due to voltage fluctuation. The most special kind of resistance is the superconductor element, which does not generate heat when conducting electricity. When it is made into computer components, it does not need a cooling system, which can greatly reduce the volume and energy consumption of the computer.
Application and development of resistance
In the above section, four functions of resistance are introduced: voltage division, shunt, impedance matching and filtering,