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Flourish Group to explain what is the role of the varistor, varistor
   Clicks:  Updated:2012-12-03 18:12:07

What is the "varistor"
Varistor mainland China noun, meaning "resistance value in the range of certain current and voltage with the voltage change", or is the resistance value of the voltage sensitive resistor English name of "Voltage Dependent Resistor" abbreviated as "VDR".
The resistor body of the varistor material is a semiconductor, so it is a species of the semiconductor resistor. Now extensive use of the zinc oxide (ZnO) varistor, divalent element (Zn) and hexavalent element oxygen (O) constituting its body material. Therefore, from the point of view of the material, the zinc oxide varistor is a "the Ⅱ - VI family oxide semiconductor.
China Taiwan, the varistors are named according to their use, called "surge absorber. Varistor according to their use is sometimes known as "electric shock (surge) suppressors (absorber)".
2, the varistor circuit "safety valve" role
Varistor what's the use? The biggest characteristic of the varistor when the "UN" when the voltage applied on top of it is below its threshold, the current flowing through it is extremely small, the equivalent of a shut valve, when the voltage exceeds UN, stream over its current surge, equivalent to the valve open. Using this feature, you can suppress the the often abnormal overvoltage circuit protection circuitry from over-voltage damage.
3, application type
Use of different occasions, the application purpose of the varistor, the varistor voltage / current stress is not the same,
Thus, the requirements of the varistor is not the same, note the distinction between this difference, it is very important for proper use.
Depending on the intended use, the varistor area is divided into two categories: ① protection varistor ② circuit functions Varistors for use.
3.1 protection with varistor
(1) distinguish between power protection with the signal line, a data line protection varistors, they are to meet the requirements of different technical standards.
(2) depending on the continuous operating voltage applied to the varistor, the cross-power line varistors District is divided into exchanges with or DC with two types of varistors in both voltage stress performance of different aging characteristics.
(3) According to the varistor withstand abnormal over-voltage characteristics of different, may be the pressure-sensitive resistor region into surge suppression, high-power and high energy type of these three types.
★ surge suppression: for to suppress lightning over-voltage and operating voltage, etc. transient over voltage varistor, this transient over voltage appear random, non-periodic, current and voltage peak may large. The vast majority of the varistor fall into this category.
★ high power type: varistor continuous burst for the absorption cycle, such as varistors and connected to the switch on the power converter, impulse voltage cycle, and the cycle we can see, the energy value generally can calculated, and the peak of the voltage is not large, but the high frequency of appearance, its average power is quite large.
★ high-energy type: the type of application, the main technical indicators is the energy absorption capacity for the absorption of the the generator excitation coil, lifting large solenoid coil inductance coil magnetic energy varistor voltage.
Varistor protection function, the vast majority of applications, can be repeated role, but sometimes it is made as a "one-time" protection current fuse devices. For example, and then some current transformer load with short circuit contact varistor.
3.2 circuit functions with varistor
The varistors are mainly used in transient overvoltage protection, but it's similar to the semiconductor zener voltage characteristics, and also it has a variety of circuit elements, for example, can be used as:
(1) DC high voltage current regulator components, its stable voltage can be as high as several thousand volts, this can not be achieved by silicon regulator.
(2) The voltage fluctuation detection element.
(3) DC bottle displacing element.
(4) of the equalizing element.
(5) Fluorescent actuation element

4, to protect the basic performance of the varistor
(1) protection characteristics, the impact strength of the impact source (or shock current ISP = USP / Zs) does not exceed the predetermined value, the limit voltage of the varistor is not allowed to exceed the object to be protected can withstand the impact resistance to a voltage (URP) .
(2) impact resistance, the varistor itself should be able to withstand the impact of the provisions of the current impact energy and average power of several attacks have appeared.
(3) Life characteristics of the two continuous working voltage life, i.e. the varistor at a predetermined ambient temperature and system voltage conditions should be able to work reliably predetermined time (hrs). The second is the impact of life, that is able to reliably withstand the impact of the specified number of times.
(4) varistor intervention system, in addition to play a "safety valve" protective effect, but also brought some additional impact, this is the so-called "secondary effects", it should not reduce the normal performance. At this time there are three main factors to be considered, varistor capacitance (tens to tens of thousands of PF), and the second is the leakage current in the system voltage, three varistors nonlinear current source impedance coupling to other circuits.

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