Varistor: the principle of operation, characteristics, purpose. How does the varistor work?

A varistor is called a semiconductor resistor, which is capable of reducing the resistance by a factor of 10 from the initial value by increasing the voltage. For example, if the resistor has a resistance of 1000 MΩ, then using this element it will be 1000 Ohm. Thus, the resistance decreases when the voltage increases.

As a rule, they are metal oxide or oxide-zinc. If we look at the varistor-ampere characteristics of the varistor, then it can be noted that it has a non-linear symmetrical shape, that is, it can work not only on a constant but also on an alternating voltage. Such an element is connected in parallel with the load. How does the varistor work? When the voltage in the network rises, the current does not pass through the equipment, but through the varistor. Such a device is capable of distributing energy in the form of heat. Its main features are multiple use and fast recovery time, that is, its resistance has an initial value when the voltage is removed.

What is the varistor principle of operation? The part does not differ from the usual resistor, that is, under normal functioning of electronics, it has ohmic resistance. So, let's look at the varistor principle of operation.

The indicator of such resistance is quite high, and can amount to 100,000 Ohm. When the voltage is turned on, it can decrease as soon as there is a need to protect the level. The resistance drops from 100,000 Ω to 100. If the value falls to a low limit or is zero, a short circuit may occur . In this case, the fuse, which is in the electrical circuit before the varistor, is out of order. After this, the electrical circuit is closed and the voltage is completely turned off.

As mentioned earlier, in the absence of voltage, the varistor can fully recover and operate in the same mode. To replace it, replace the blown fuse. Then the electronic device will function correctly. The varistor is connected in parallel to the power supply. Let's consider, what the varistor principle of work has, on an example of the usual personal computer. Since it has two terminals, the connection is made parallel to the phase and zero.

What does the element look like?

Such an adaptation, like a varistor, the photo of which is in our article, resembles a conventional resistor, that is, it has the shape of a rectangle. But still has a slight difference. In the middle of it there is a diagonal, the end of which is curved.

How is the varistor labeled?

To date, you can find different designations for these devices. Each manufacturer has the right to install it independently. The markings differ, because the technical characteristics of the varistors differ from each other. Examples include indicators such as the allowable voltage or the required current level.

Currently, each manufacturer sets its marking on these types of devices. This is because the devices produced have different technical characteristics. For example, the maximum permissible voltage or the current level required for operation. The most popular marking is CNR, to which the designation 07D390K is attached. What does this mean? So, the very designation CNR indicates the type of device. In this case, the varistor is metal oxide.

Next, 07 is the size of the device in diameter, that is equal to 7 mm. D is a disk device, and 390 is the maximum permissible voltage.

The main parameters of the varistors

These parameters include:

• Stress rate;
• Maximum permissible index of alternating and direct current;
• Peak energy absorption;
• Possible errors;
• The working time of the element.

Diagnostics

To check this electronic device, use special equipment, which is called a tester. So, to carry out the test, you need a varistor, the principle of which is to change the resistance parameters, and the testing device. Before it starts, you must turn on the device and switch to resistance mode. Only then will the device meet all the necessary technical requirements, and the magnitude of the resistance will be enormous.

Before starting the tests, it is necessary to check the technical condition of the device. First of all, you should look at its appearance. The device should not have cracks, as well as signs that it is burnt. Do not treat the inspection of the device negligently, as any small breakdown can lead to unpleasant circumstances.

Varistors: application

Such devices play an important role in human life. From all of the above, we can say that the varistor, whose operation principle is to protect the electronics from high voltage in the network, helps prevent the breakdown of many electrical appliances and keep the wiring intact. The main place is electrical circuits in various equipment. For example, they are found in lighting elements, which are also called ballasts. Also installed in the electrical circuits are special varistors, the use of which is necessary for the stabilization of voltage and current. Such devices are used in power lines. But there they are called dischargers, the working voltage of which is more than twenty thousand volts.

Varistors can operate in a wide voltage range, which starts at a very low value of 3 V, and ends at 200 V. As for the cell current, the range is from 0.1 to 1 A. These current values are valid only for low-voltage technical equipment .

The positive side of the varistors

This type of apparatus has many positive qualities, if we compare it with other devices, for example, with a spark gap. To such important advantages it is possible to carry:

• High speed of the element;
• The ability to monitor current transients by the inertia-free method;
• The possibility of using at a voltage level between 12 and 1800 V;
• Long service life;
• Relatively low cost due to the simplicity of the design.

Negative sides

Together with so many advantages over other devices, there are also significant drawbacks, among which one can distinguish such.

1. Varistors have a huge size of their own capacity, which affects the operation of the electrical network. Such an indicator can be in the range from 80 to 3000 pF. It depends on many factors: the design and type of the varistor, as well as the maximum value of the voltage level. It is worth noting that in some cases such a significant defect can turn into a major advantage. But this is quite rare, for example, if you use a varistor in filters. In this situation, a large capacity will serve as a voltage limiter in the network.
2. In comparison with arresters, varistors are not able to dissipate power at maximum voltage levels.

To increase the number of absent-mindedness, it is necessary to increase the size of the elements, which many manufacturers are engaged in.

Recommendations for installation

If there is a need to include a varistor in an electrical network, it is necessary to remember about such important points:

• It should always be borne in mind that this device is not eternal, and there will come such conditions that will lead to its explosion. To avoid this, it is necessary to use special protective screens in which you can place the entire varistor.
• It should be noted that flint technical devices are significantly inferior in their characteristics to oxide analogs. Therefore, it is best to use this kind of varistor.

Conclusion

Varistor plays an important role in the functioning of many electrical circuits. As mentioned earlier, this kind of semiconductor resistors serves to reduce the resistance values with increasing voltage or current. Due to this possibility they are installed in many electrical appliances. With voltage jumps, the varistor, whose purpose is to change the resistance, does not allow devices to break down. Also it prevents burnout of the wiring. Thus, these elements provide reliable protection in case of jumps in the electrical voltage in the network.