1, what is the "pressure sensitive resistance"
"The pressure sensitive resistance is a term in the mainland of China, which means" the value of the resistance varies with the voltage in a certain current voltage range, or the resistance value of the resistance value is sensitive to the voltage. The corresponding English is called "VoltageDependentResistor" or "VDR".
The material of the resistor is a semiconductor, so it is a variety of the semiconductor resistor. Now a large number of use of "Zinc Oxide" (ZnO) pressure sensitive resistor, which is the main material has two valence elements (Zn) and six valence element oxygen (O) constitute. So from the material point of view, Zinc Oxide varistor is a kind of "II-VI semiconductor oxide".
In Taiwan China, varistors are named according to their use, called "surge absorber". Varistor according to its use is sometimes referred to as "electric shock (surge suppressor) (absorber)".

2, the "safety valve" role of the pressure sensitive resistance circuit
What is the use of pressure sensitive resistance? The biggest characteristic of the varistors with them when the voltage is lower than the threshold it "UN", the minimum current flowing through it, the equivalent of a closed valve, when the voltage exceeds UN, the current flowing through it in the equivalent of the valve open. By using this function, the abnormal overvoltage can be suppressed in the circuit, which can protect the circuit from excessive voltage.

3, application type
For different applications, the purpose of the application of the pressure sensitive resistance, the role of the voltage / current stress on the pressure sensitive resistance is not the same,
Therefore, the requirements of the pressure sensitive resistance is not the same, pay attention to distinguish the difference, for the correct use is very important.

4, circuit function with the pressure sensitive resistance
The pressure sensitive resistor is mainly used for transient overvoltage protection, but it is similar to the volt ampere characteristic of the semiconductor voltage regulator tube, and also has the function of various circuit elements:
(1) the DC high voltage small current voltage stabilizing element, its stable voltage can be as high as thousands of volts above, this is the silicon voltage regulator tube can not achieve.
(2) voltage fluctuation detection element.
(3) DC battery shift element.
(4) all pressure components.
(5) fluorescence starting element

5, protection of the basic properties of the pressure sensitive resistance
(1) protection characteristics, when the impact of the shock source (or the impact current Isp=Usp/Zs) does not exceed the specified value, the limit voltage of the voltage sensitive resistance is not allowed to exceed the protected object can withstand the impact of voltage resistance (Urp).
(2) shock resistance characteristics, that is, the pressure sensitive resistance itself should be able to withstand the provisions of the impact current, impact energy, as well as the average power.
(3) there are two life characteristics, one is the continuous working voltage life, that is, the pressure sensitive resistance in the specified ambient temperature and system voltage conditions should be able to reliably work the specified time (hours). Two is the impact of life, that can be reliably under the provisions of the impact of the number of.
(4) after the intervention system, in addition to the "safety valve" of the protective effect, but also to bring some additional impact, this is the so-called "two effects", it should not reduce the normal operating performance of the system. The factors to consider when there are three, one is capacitance varistor itself (tens to tens of thousands of PF), the two is the leakage current in the system voltage, three nonlinear current varistor effect on other circuits by coupling the source impedance.


From the electronic related article:

　　Correct use of pressure sensitive resistors

　　Detailed reference parameters of varistor