The varistor is used in electronics and is installed to provide protection of devices from voltage surges. Its resistance can vary and depends on the voltage supplied to the device, it varies in the range from 100 MΩ to 10 Ohms. How varistors work, their principle of operation, main characteristics and parameters - if desired, these issues can be understood by a non-specialist.
Content
- The principle of operation of the device
- Classification and benefits
- Manufacturing technology and parameters
- Marking and designations
The principle of operation of the device
Under standard conditions, the varistor has a high resistance, but when the voltage is exceeded, the resistance drops, and the current increases due to the avalanche effect. In the device itself at this moment, the voltage is slightly higher than the norm.
In this mode, its operation can be compared with a zener diode. When designing a circuit with a varistor connection, it must be borne in mind that it also has a capacitance. The volume of this container is inversely proportional to the thickness and directly proportional to the area.
In order to choose the right element that protects against power overload, one should take into account not only the power of the pulses, but also the input resistance that appears during transient processes. If the device is incorrectly selected, and its maximum value turns out to be small, then it will become very hot, which will damage the device itself and, possibly, the device as a whole.
Classification and benefits
Semiconductor resistors are classified according to operating voltage. The voltage is divided into the following types: up to 20 kV and from 2.8 to 220 V.
The first of them are called high voltage. They have found their application in electronic networks, and the latter are called low-voltage and are installed in electrical appliances and household devices for the purpose of protection.
Among the advantages of this device, it should be noted its unique ability to work with heavy loads, as well as at high frequencies. In addition, the benefits include:
- cheapness;
- high prevalence;
- simplicity of design;
- reliability.
The disadvantages of this resistor include an increase in the temperature of the device as a whole, as well as an increase in low-frequency noise.
Manufacturing technology and parameters
When making a varistor, two powders are used:
- zinc oxide;
- silicon carbide.
The main manufacturing technology consists in firing all elements at high temperatures in a furnace and simultaneously pressing them. The resulting product is coated with waterproof and insulating varnish. This technology is called ceramic and allows custom-made varistor manufacturing.
Semiconductor type resistors are characterized by the following features:
- nominal classification voltage;
- maximum permissible alternating voltage;
- voltage is possible permissible constant;
- maximum limiting voltage (when increasing, the device breaks down);
- energy absorbed maximum.
Almost all varistors have a response time of tens of nanoseconds. The tolerance is indicated by ± 5%, ± 10%, ± 20%, etc.
Marking and designations
In order to understand which varistor is presented, and what characteristics it has, you need to understand what the letters and numbers on the case of each element mean. Their correct decoding will tell you about its exact parameters.
The element type is indicated by the first letters. For example, nonlinear resistance is denoted - CH. Next, the letters are followed by a number, which indicates what material the varistor is made of. If the number is 1, then the material used in the manufacture is silicon carbide.
Also, the number that is between the two hyphens indicates the type of construction. If there is a number 1, then the product has a rod-type design, and if there is a number 2, then a disk one. Subsequent numbers indicate the nominal voltage and the permissible deviation, respectively, which is indicated in percent.
If you need to find out if the device is operational, then you need to perform several actions. First, the varistor should be inspected for damage or other visual defects (blackening, darkening, microcracks). If the above deficiencies are found, then you should refuse to use such a device and replace it with a new one, since it will not perform its function (it may be, but not in full).
Secondly, you should use an ohmmeter or multimeter to measure resistance. If the indicators do not correspond to the norm, then such a device should also be abandoned.
A varistor is a reliable resistor made of semiconductor material that effectively protects electrical appliances from overloads and voltage surges. With a sharp increase in the mains voltage, it takes the entire load on itself, thereby preventing the device in which it is installed from burning out. Therefore, it is the simplest, cheapest and most reliable protection.
