How to use plug-in varistor correctly? According to different usage scenarios, the purpose of applying a varistor is that the voltage / current stress acting on the varistor is not the same, so the requirements for the varistor are also different. Pay attention to distinguish this difference.
According to different uses, plug-in varistor is divided into: plug-in varistor for circuit function and plug-in varistor for protection.
A. Plug-in varistor for circuit function
The plug-in varistor is mainly used for transient overvoltage protection, but its volt-ampere characteristics similar to semiconductor voltage regulators also make it have a variety of circuit element functions, the role is:
(1) DC high-voltage small-current voltage stabilizing element, its stable voltage can be as high as several thousand volts or more, which is beyond the reach of silicon voltage regulators.
(2) Voltage fluctuation detection element.
(3) DC battery displacement element.
(4) Pressure equalizing element.
(5) Fluorescence start element.
B. Plug-in varistor for protection
(1) Distinguish between power supply protection, signal line and data line protection varistor, they must meet the requirements of different technical standards.
(2) Depending on the continuous operating voltage applied to the varistor, the varistor across the power line can be divided into two types for AC or DC. The varistor under these two voltage stresses Aging characteristics are different.
(3) The varistor can be divided into three types: surge suppression type, high-power type and high-energy type according to the abnormal overvoltage characteristics of the plug-in varistor.
Surge suppression type: refers to a varistor used to suppress transient overvoltages such as lightning overvoltage and operating overvoltage. The occurrence of such transient overvoltages is random and non-periodic, and the peak value of current and voltage may be very high Big. Most varistors fall into this category.
High-power type: refers to a varistor used to absorb continuous pulse groups that occur periodically, such as a varistor connected in parallel to a switching power supply converter, where the impulse voltage cycle occurs, and the cycle is known, and the energy value can generally be calculated Out, the peak voltage is not large, but because of the high frequency, its average power is quite large.
High-energy type: refers to a varistor used to absorb magnetic energy in large-scale inductance coils such as generator excitation coils and lifting electromagnet coils. For such applications, the main technical indicator is energy absorption capacity.
The protection function of the plug-in varistor can be repeated many times in most applications, but sometimes it is also used as a "one-time" protection device like a current fuse. For example, a varistor with a short-circuit contact connected in parallel to certain current transformer loads.