DCF type safety ceramic capacitor 103M
Varistors for protection and circuit functions
Different use occasions, the purpose of applying the varistor, the voltage/current acting on the varistor should be different, so the requirements for the varistor are also different, it is very important to pay attention to distinguish this difference for the correct use of.
According to the purpose of use, varistors can be divided into two categories: ① varistors for protection, ② varistors for circuit functions.
Protection resistor
(1) Distinguish whether it is a varistor for power protection or a varistor for signal line and data line protection, which must meet the requirements of different technical standards.
(2) According to the continuous working voltage applied to the varistor, the varistor used across the power line can be divided into two types: AC or DC. The aging of the varistor under these two voltage stresses Features behave differently.
(3) According to the different abnormal overvoltage characteristics of the varistor, the varistor can be divided into three types: surge suppression type, high power type and high energy type.
★Surge suppression type: refers to a varistor used to suppress transient overvoltages such as lightning overvoltage and operating overvoltage. The appearance of such transient overvoltages is random and aperiodic, and the peak value of current and voltage may be very large. The vast majority of varistors fall into this category.
★High-power type: It refers to the varistor used to absorb the continuous pulse group that occurs periodically, such as the varistor connected in parallel to the switching power converter, where the impulse voltage occurs periodically, and the cycle can be known, and the energy value can generally be It is calculated that the peak value of the voltage is not large, but the average power is quite large due to the high frequency of occurrence.
★High-energy type: refers to the varistor voltage device used to absorb the magnetic energy in the large-scale inductive coils such as generator excitation coils and hoisting electromagnet coils. For such applications, the main technical indicator is energy absorption capacity. The protection function of the varistor can be repeated many times in most applications, but sometimes it is also made into a "one-time" protection device like a current fuse. For example, a varistor with short-circuit contact connected in parallel with some current transformer loads.
